Phylum Arthropoda

Phylum Arthropoda (von Siebold, 1845)

By nearly any measure, the most successful animals on the planet are the arthropods. They have conquered land, sea and air, and make up over three-fourths of all currently known living and fossil organisms, or over one million species in all. Since many arthropod species remain undocumented or undiscovered, especially in tropical rain forests, the true number of living arthropod species is probably in the tens of millions. One recent conservative estimate puts the number of arthropod species in tropical forests at 6 to 9 million species (Thomas, 1990).

Arthropods range in distribution from the deep sea to mountain peaks, in size from the king crab with its 12-foot armspan to microscopic insects and crustaceans, and in taste from chocolate covered ants to crawfish jambalaya and lobster Newburg. Despite this unbelievable diversity, the basic body plan of arthropods is fairly constant. Arthropods have a stiff cuticle made largely of chitin and proteins, forming an exoskeleton that may or may not be further stiffened with calcium carbonate. They have segmented bodies and show various patterns of segment fusion (tagmosis) to form integrated units (heads, abdomens, and so on). The phylum takes its name from its distinctive jointed appendages, which may be modified in a number of ways to form antennae, mouthparts, and reproductive organs.

Phylum Arthropoda (von Siebold, 1845)

Aglais milbertiScutigera coleoptrata

Nephila senegalensis

Petrochirus diogenes

Phylum Arthropoda (von Siebold, 1845)

Subphylum Hexapoda

The most distinctive feature of the hexapods is the reduction in walking appendages to six, with three body segments consolidating to form the thorax, which provides much of the locomotory ability of the animals. (This is in contrast to other arthropods, most of which have more than three pairs of legs.)

Monobella grassei Campodeid (Diplura)

Class Collembola

Class Collembola

Among the prominent derived characteristics of this group are:• ventral tube ("collophore") on segment 1 of abdomen (adhesive

in some groups, but primarily involved with excretion and water transport)

• springing mechanism formed from retinaculum on segment 3, furcula on segment 4

• 4-segmented antennae (segments sometimes subsegmented, giving the appearance of more than 4 segments)

• 6 abdominal segments Other characteristics include:• indirect sperm transfer with globular stalked spermatophore • Some Neanuridae have polytene chromosomes • Adults continue moulting throughout life (up to 50 moults) • Reproductive instars alternate with feeding instars • Cerci lacking

Class Collembola

Collembola

Symphypleona Collembola

Order Poduromorpha

Podura aquatica

Anurida granaria

Family:PoduraOnychiuridaeHypogastruridae (non-monophyletic) BrachystomellidaeOdontellidaeNeanuridae

Are elongate, with separated abdominal segments, however, they have a well developed prothorax.

Order Symphypleona

Dicyrtoma fusca

Sminthurides aquaticus

Family:KatiannidaeSpinothecidaeBourletiellidaeMackenziella psocoidesDicyrtomidaeSminthuridaeSminthurididaeSturmiusArrhopalitidae

Are globular, with fused abdominal segments, however, they have eyes and antennae longer than their head.

Order Neelipleona

Family: Neelidae

Megalothorax minimus

Megalothorax minimus

dorsal

lateral

Are globular, with fused abdominal segments, no eyes, and antennae shorter than their head.

Order Entomobryomorpha

Entomobrya nicoleti Orchesella alticola

FamilyEntomobryidaeIsotomidae Oncopoduridae Tomoceridae

Are elongate, with separated abdominal segments and a reduced prothorax.

Order Protura

Derived characteristics: eyeless antennae absent tentorium absent fore legs enlarged, with

many sensilla; front legs serve role of antennae

Other characteristics:

•very small, less than 2 mm long •abdomen with 12 segments as adult •Mouth parts entognathous •cerci absent •legs 5-segmented •anamorphic development (segments added at moults) vs. epimorphic in all other hexapods

Order Protura

Protura

SinentomataAcerentomataEosentomata

Order Diplura

Among the derived features of diplurans are: eyeless tentorium absent unique muscles and pivots in legs

Other characteristics: mostly white two prominent cerci, either long and filiform or

short and forcep-like long, slender antennae

Order Diplura

Japygidae Campodeid (Diplura)

Family:•Campodeidae •Procampodeidae •Projapygidae •Anajapygidae •Japygidae •Heterojapygidae •Dinjapygidae •Evalljapygidae •Parajapygidae •Onychojapyx schmidti•Plioprojapyx primitivus

Class Insecta Insects have a large number of unique, derived

characteristics, although none of these are externally obvious in most species. These include (Kristensen, 1991):

lack of musculature beyond the first segment of antenna. Johnston's organ in pedicel (second segment) of antenna.

This organ is a collection of sensory cells that detect movement of the flagellum.

a transverse bar forming the posterior tentorium inside the head

tarsi subsegmented females with ovipositor formed by gonapophyses from

segments 8 and 9 annulated, terminal filament extending out from end of

segment 11 of abdomen (subsequently lost in most groups of insects)

Class Insecta

Class Insecta

Machilidae Thermobia domestica

Lestidae

Subclass Archaeognatha

Recent archaeognathans share two notable derived features:

Compound eyes enlarged, medially contiguous

Specialized musculature of abdomen, which allows them to jump by a rapid downward bending

Archaeognathans also share a number of primitive features. Their mandibles are monocondylic, that is, with only one condyle (the joint or socket-like attachement point to the head capsule), whereas other insects have two condyles ("dicondylic"). This primitive mouthpart feature gives the order its name (Arche - beginning, gnathos - jaw).Their abdominal segments bear styles, which are small appendages moveable by muscles. They can be seen underneath the abdomen in the following picture:

Styli may be remnants of ancestral limbs.

Archaeognatha

Subclass Thysanura

Characteristics: body flattened long cerci and median filament compound eyes separate

Thermobia domestica

Subclass Thysanura

Subclass Pterygota

The primary derived characteristic of pterygotes is the presence of veined wings on the second (meso-) and third (meta-) thoracic segment.

Subclass Pterygota

Libellula saturata

Ephemera danicaEchinargus isola

Order Paleodictyopteroidea Palaeodictyopteroid insects share a unique mouthpart morphology. Their clypeus is much enlarged, and they have a distinctive beak formed by five elongate, stiff elements.

Breyeria borinensis

Handlirsch, A. 1904

Order Ephemeroptera

Derived characteristics: Fore legs of male elongated, used to grasp female in flight. mouthparts of adults reduced, unsclerotised. hind wings reduced, smaller than fore wings. In addition, mayflies moult after they have fully-formed, functional wings. Presence of a winged, pre-adult stage ("subimago") is unique among insects.

Hexagenia sp.

Ephemeroptera

Order Odonata (Fabricius,1793)

Argia

Sympetrum sanguineum

These insects characteristically have large rounded heads covered mostly by well-developed, compound eyes, legs that facilitate catching prey (other insects) in flight, two pairs of long, transparent wings that move independently, and elongated abdomens. They have two ocelli and short antennae. The mouthparts are on the underside of the head and include simple chewing mandibles in the adult

Suborder AnisopteraFamily Aeshnidae

Anax junius

Family Cordulegastridae

Cordulegaster bilineata

Dromogomphus spinosus

Family Gomphidae

Suborder Zygoptera

Family Calopterygidae

Calopteryx maculataArgia fumipennis

Family Coenagrionidae

Lestes rectangularis

Family Lestidae

Infraorder Neoptera

Neopterous insects primitively have the ability to fold the wings back over their abdomen, using special structures at the base of their wings. Key to the folding mechanism is the third axillary sclerite and pleural wing-folding muscle. This ability to fold the wings back over the abdomen has been lost in some small groups within Neoptera, including various butterflies and moths.

Dactylotum variegatum

Halictidae

Pyrrhocoris apterus

Infraorder Neoptera

Order PlecopteraStoneflies are easily recognized by a few simple characters. They have three segmented tarsi but their hind legs are not modified for jumping to the extent of Orthoptera such as crickets and grasshoppers. They have long filiform antennae at least half length of the body. The cerci are generally long as well, especially in the aquatic nymphs. The wings are almost always present but are sometimes very short. They are folded horizontally back over the body. These characters help distinguish them from Dermaptera and Embioptera which they superfically resemble and to which they are probably closely related.

The immatures are variously called larvae, or nymphs or naiads, but are most frequently referred to as nymphs. All nymphs are aquatic, and resemble the adults in many respects. They also have three-segmented tarsi. The nymphs always have long cerci and never a third central tail or median caudal filament. Gills, if they have them, can occur on various parts of the thorax and abdomen and are composed only of filaments, not plates.

Order Plecoptera

Perlesta decipiens (Walsh, 1862)

Triznaka signata (Banks, 1895)

Family Perlodidae

Synapomorphies for Peltoperlidae: 1, body stout, head prognathous, cockroach-like nymphal body form; 2, male cercal segments fused; 3, nymphal coxae with flap-like lobe.

Hydroperla crosbyi (Needham & Claassen, 1925)

Family Nemouridae

Zwick (1973) listed four synapomorphies for the Nemouridae: 1, with testes large, long, and radiating from the anterior bend of the vas deferens in the shape of a star; 2, abdominal ganglia reduced to five; 3, last segment of the labial palpi large, round, and flattened; 3, the shape and site of insertion of the coxae. Baumann (1975) listed the synapomorphies for Amphinemurinae: 1, three lobed paraprocts; 2, paraprocts armed with spines or prongs. He listed the synapomorphy of the Nemourinae as having a ventral sclerite of the epiproct enlarged and with a very broad base.

Family Nemouridae

Soyedina washingtoni (Claassen, 1923)

Family Pteronarcyidae

Zwick (1973) lists the synapomorphies of the Pteronarcyidae as: 1, ventral lobe reduced; 2, trachea leading from head to cervical gills; 3, postfurcal gills present. Uchida & Isobe (1989) state that the arolium of the pretarsus is expanded laterally, with a pair of lateral sclerites.

Family Pteronarcyidae

Pteronarcys californica Newport, 1848

Order Orthoptera (Latreille, 1793)

The name Orthoptera is derived from "orthos" meaning "straight" and "pteron" = "wing."Shared-derived characters: in addition to the saltatory hind legs, most orthopterans have small and well separated hind coxae, a pronotum with large descending lateral lobes, nymphal wing rudiments reversing their orientation in later instars and hind tibiae with two dorsal teeth rows (Kevan 1982; Kukalova-Peck 1991; Rentz 1991). Other characteristics are unsegmented cerci and leathery forewings.

Orthoptera

Suborder EnsiferaThe antennae are fine and threadlike (well over 30 segments) except in the completely fossorial Cooloolidae. In the singing families there are stridulatory specializations of the forewings which include a toothed vein (file) and scraper, and membranous areas that resonate or amplify sounds. In these groups ears consist of foretibial tympanae linked via modified tracheae to the enlarged mesothoracic spiracles that are modified for an auditory function. The tarsi have three to four segments. The six-valved ovipositor (when present) is sword-like ('ensiform', thus the subordinal name) or needle-like (Chopard 1920; Kevan 1982; Rentz 1991, 1996). Ensiferan mandibles are elongate and possess a prominent incisor. The gut's proventriculus consists of a globular body lying between two bulbous gastric caeca. Internally there are six longitudinal folds that bear appendages (Judd 1947; Rentz 1980). The spermatophore in virtually all species is attached externally to the female's gonopore; it has a double (or partially divided) sperm reservoir in most Tettigonioidea (some Rhaphidophoridae and Deinacrida species (Stenopelmatidae) are exceptions) and a single one in true crickets and their allies. In many taxa (most tettigonioids and some true crickets) a spermatophylax (meal for the female) surrounds the spermatophore (Boldyrev 1915; Gwynne 1995).

Suborder Ensifera

Cooraboorama canberrae Metholche nigritarsus

Family Haglidae

The haglids were very diverse from the late Permian to the early Cretaceous (Sharov 1968; Storozhenko 1997), but only five relict species survive today. These are the short-winged Paracyphoderris erebeus and three species of Cyphoderris (Haglinae) (females are micropterous); and the macropterous Prophalangopsis obscura (F. Walker) (Prophalangopsinae) described from a single male specimen collected in northern India in the mid 1800s (Caudell 1911).

Cyphoderris strepitans

Family TettigoniidaeThe use of vegetation by katydids during periods of inactivity contrasts with the retreat to a burrow or crevice by other ensiferans. These differences appear to be reflected in structure; ensiferan taxa that burrow tend to have forewings that wrap around the body whereas the tegmina of katydids, unconstrained by burrow use, can be held away from the body as "roof-like" structures and modified for acoustical and/or leaf-mimicry purposes (references in Gwynne 1995).

Forewing characters that appear to be synapomorphic include a left - over - right overlap of the singing wings in males, a fully - functional stridulatory file on the underside of the left wing and a vestigial file on the right wing. Other synapomorphies include four tarsal segments (also found in the haglid, Prophalangopsis obscura) and, for five species representing four subfamilies, nuclear RNA sequences (Flook and Fraser-Rowell, submitted MS).

Family Tettigoniidae

Family Tettigoniidae

Phasmodes ranatriformis (Phasmodinae)

Anabrus simplex

Metholche nigritarsus (Conocephalinae)

Suborder Caelifera

Among other synapomorphies the Caelifera is distinguished from the Ensifera by the structure of the ovipositor, in which the original 6 valves are reduced to 4 functional ones with transverse musculature, by antennae composed of less than 30 segments, and by the absence of auditory organs on the prothorax - if a tympanum or other hearing organ is present, it is abdominal. The sperm are thin and elongate, with an acrosome inserted on the nucleus by means of two lateral processes.

Suborder Caelifera

Agriacris tricristata Thericles zebra

Tetrigoidea

Superfamily Acridoidea

Brachystola magna

Acrida ungarica

Family:AcrididaePamphagidaeLathiceridaeCharilaidae (= Pamphagodidae)RomaleidaeOmmexechidaeTristiridaeLentulidaePyrgacrididae

Subphylum Crustacea (Brünnich, 1772)

Crustaceans differ from other arthropods in a variety of ways, but the only truly distinguishing characteristic is that crustaceans are the only arthropods with two pairs of antennae. In addition to two pairs of antennae and a pair of mandibles, crustaceans have two pairs of maxillae on the head, followed by a pair of appendages on each body segment or somite.

Daphnia pulex

Grapsus grapsus

Lepas anatifera

Subphylum Crustacea (Brünnich, 1772)

Subphylum Crustacea (Brünnich, 1772)

Class Branchiopoda

Class Branchiopoda

Branchiopods have reduced first antennae and second maxillae. Their legs are flattened and leaflike (phyllopodia) and are the chief respiratory organs (hence the name branchiopods). Most branchiopods also use their legs for suspension feeding, and in groups other than the cladocerans, they use their legs for locomotion as well.

Lepidurus packardi

Order Anostraca

Fairy shrimp. Trunk with 11-18 segments.

Order Notostraca

Tadpole shrimp. Thorax with appendages, abdomen without appendages. Thorax covered by carapace.

Order Cladocera

Water fleas. Trunk enclosed in bivalved carapace. Head with single, median, compund eye. Second antennae elaborated for swimming. 4-6 pairs of trunk appendages. Mostly freshwater.

Ceriodaphnia megalops

Ceratia sp.

Class Remipedia

Class Remipedia

Speleonectes ondinae (Speleonectidae).

Remipedia is a very small, recently described class of Crustacea.The 10 species described so far have come from caves with connections to the sea. Remipedes have some very primitive features. There are 25 to 38 trunk segments (thorax and abdomen), all bearing paired, biramous, swimming appendages that are all essentially alike. Antennules are biramous. Both pairs of maxillae and a pair of maxillipeds, however, are prehensile and apparently adapted for feeding. The shape of the swimming appendages is similar to that found in Copepoda, but unlike copepods and cephalocarids, swimming legs are directed laterally rather than ventrally.

Class Cephalocarida

Hutchinsoniella sp. Pratt, 1923.

HutchinsoniellaLightiellaChiltonellaSandersiellaHampsonellus

They are 2 to 3 mm long and have been found in bottom sediments from the intertidal zone to a depth of 300 m. Some of their features are quite primitive. Thoracic limbs are very similar to each other, and second maxillae are similar to thoracic limbs. The second maxillae and the first seven thoracic legs have a large epipod on their protopod, and the protopod is a single joint. Cephalocarids have no eyes, carapace, or abdominal appendages. True hermaphrodites, they are unique among Arthropoda in discharging both eggs and sperm through a common duct

Class Ostracoda (Latreille, 1802)

Members of Ostracoda are, like conchostracans, enclosed in a bivalve carapace and resemble tiny clams, 0.25 to 8 mm long. Ostracods show considerable fusion of trunk somites, and numbers of thoracic appendages are reduced to two or none. Feeding and locomotion are principally by use of the head appendages. Most ostracods live on the bottom or climb on plants, but some are planktonic or burrowing, and a few are parasitic. Feeding habits are diverse; there are particle, plant, and carrion feeders and predators. They are widespread in both marine and freshwater habitats. Development is gradual metamorphosis.

Ostracoda

Class Mystacocarida 1943

Mystacocarida is a class of tiny crustaceans (less than 0.5 mm long) that live in interstitial water between sand grains of marine beaches (psammolittoral habitat). Only 10 species have been described, but mystacocarids are widely distributed through many parts of the world.

Class Copepoda

This group is second only to Malacostracain numbers of species. Copepods are small (usually a few millimeters or less in length) and rather elongate, tapering toward the posterior. They lack a carapace and retain the simple, median, nauplius (maxillopodan) eye in adults . They have asingle pair of uniramous maxillipeds and four pairs of rather flattened, biramous, thoracic swimming appendages. The fifth pair of legs is reduced. The posterior part of the body is usually separated from the anterior, appendage-bearing portion by a major articulation. Antennules are often longer than other appendages.

Aetideidae

PlatycopioidaCalanoidaMisophrioidaGelyelloidaCyclopoidaMormonilloidaHarpacticoidaPoecilostomatoidaMonstrilloidaSiphonostomatoida

Order Calanoida

Calanus pavo

Any Family:•Acartiidae •Aetideidae •Arietellidae •Augaptilidae •Bathypontiidae •Boholinidae •Calanidae •Candaciidae •Centropagidae •Clausocalanidae •Diaixidae •Diaptomidae •Discoidae •Epacteriscidae •Eucalanidae •Euchaetidae

Order Cyclopoida

Cyclops

Family:ArchinotodelphyidaeAscidicolidaeBuproridaeChordeumiidaeCucumaricolidaeCyclopidaeCyclopinidaeFratiidaeLernaeidaeMantridaeNotodelphyidaeOithonidaeOzmanidaeSpeleoithonidaeThaumatopsyllidae

Order Siphonostomatoida

Cryptopontius thorelli

Any Family:•Archidactylinidae •Artotrogidae •Asterocheridae •Brychiopontiidae •Caligidae •Calverocheridae •Cancerillidae •Cecropidae •Codobidae •Coralliomyzontidae •Dichelinidae •Dichelesthiidae •Dinopontiidae •Dirivultidae •Dissonidae •Ecbathyriontidae

Class Tantulocarida

Tantulocarida is the most recently described class (here considered a subclass) of crustaceans (1983). Only about 12 species are known so far. They are tiny (0.15 to 0.2 mm) copepod-like ectoparasites of other deep-sea benthic crustaceans. They have no recognizable head appendages except one pair of antennae on sexual females. The life cycle is not known with certainty, but present evidence suggests that there is a parthenogenetic cycle and a bisexual cycle with fertilization. Tantulus larvae penetrate the cuticle of their hosts by a mouth tube. Then their abdomen and all thoracic limbs are lost during metamorphosis to the adult. Alone among maxillopodans, juveniles bear six to seven abdominal somites, but other evidence supports inclusion in this class.

A tantulocarid. This curious little parasite is shown attached to the first antenna of its copepod host at left; class Tantulocarida,

Class BranchiuraBranchiurans are a small group of primarily fish parasites, which, despite their name, have no gills. Members of this group are usually between 5 and 10 mm long and may be found on marine or freshwater fish.They typically have a broad, shieldlike carapace, compound eyes, four biramous thoracic appendages for swimming, and a short, unsegmented abdomen. Second maxillae have become modified as suction cups, enabling the parasites to move about on their fish host or even from fish to fish. Development is almost direct: there is no nauplius, and young resemble adults except in size and degree of development of appendages.

Fish louse; class Branchiura

Class Thecostraca

Lepas anatifera

Synagoga sp. (probably undescribed) on Antipathella

Infraclass Cirripedia (Burmeister, 1834)

Cirripedia includes barnacles (order Thoracica), which are usually enclosed in a shell of calcareous plates, as well as three smaller orders of burrowing or parasitic forms. Barnacles are sessile as adults and may be attached to the substrate by a stalk (gooseneck barnacles) or directly (acorn barnacles). Typically the carapace (mantle) surrounds the body and secretes a shell of calcareous plates. The head is reduced, the abdomen is absent, and the thoracic legs are long, many-jointed cirri with hairlike setae. The cirri are extended through an opening between the calcareous plates to filter from the water the small particles on which the animal feeds.

Chthamalus stellatus

Lepas anatifera

Class Malacostraca Usually with eight somites in thorax and six plus telson in abdomen; all segments with appendages; antennules often biramous; first one to three thoracic appendages often maxillipeds; carapace covering head and part or all of thorax, sometimes absent; gills usually thoracic epipod.

Hyalella azteca

Elassochirus gilli Stomatopoda

Class Malacostraca

The Malacostraca is also a large and diverse group of Crustaceans, and contains the most familiar forms, especially on dinner tables. This group is treated further in the section on Malacostraca.

The subclasses of Malacostracans are:

1.Subclass Phyllocarida (leptostracans)2.Subclass Eumalacostraca (shrimps, crabs, lobsters, amphipods, isopods, mysids, euphausids, and others)

Class Malacostraca

Subclass Phyllocarida (Leptostraca)

Nebalia bipes R. La Follette. 1914

•Nebaliopsis typica •Paranebalia longipes •Paranebalia belizensis •Nebalia antarctica •Nebalia bipes •Nebalia borealis •Nebalia brucei •Nebalia cannoni •Nebalia capensis •Nebalia chilensis •Nebalia clausi •Nebalia dahli •Nebalia daytoni •Nebalia falklandensis •Nebalia gerkenae •Nebalia herbstii •Nebalia hessleri •Nebalia ilheoensis •Nebalia japane

Subclass Eumalacostraca Order Stomatopoda

Lysiosquilla maculata

Hemisquilla californiensis (Gonodactylidae)

Mantis shrimp. Second pair of thoracic appendages large and subchelate. First antenna with three flagella. Carapace does not cover last 2 thoracic appendages. Compound eyes stalked.

All thoracic segments fused with and covered by carapace; eyes on stalks; first three pairs of thoracic appendages modified to maxillipeds.

Order DecapodaNeotrypaea californiensis

Panulirus argus

Hemigrapsus nudus

Infraorder Anomura (Macleay, 1838)

Petrochirus diogenes

Porcellanidae

Family AeglidaeAegla abtao abtao Schmitt 1942 Aegla denticulata denticulata Nicolet 1849

Infraorder Achelata (Scholtz & Richter, 1995)

Panulirus fermoristriga

Scyllaridae

Family PalinuridaeThe members of the family Palinuridae are commonly known as spiny lobsters, crawfish/crayfish, langoustes, or shrimp depending on the part of the world in which they are found (Holthuis, 1991).  They form a world-wide fishing industry and are found from cold, deep waters up into shallow coral reefs.  Palinurids have spiny antennae, lack claws and most species produce loud sounds using structures at the base their antennae.

Panulirus penicillatus

Palinurus elephas

Superorder Peracarida (Calman, 1904)

The superorder Peracarida is a large group of crustaceans, having members in marine, freshwater, and terrestrial habitats. They are defined by the possession of a single pair of maxillipeds (rarely 2–3), of mandibles with an articulated accessory process between the molar and incisor teeth in the adults (called the lacinia mobilis), and of a carapace which is often reduced in size and is not fused with the posterior thoracic somites. In all orders except the Thermosbaenacea, where the carapace is used to brood eggs, the basalmost segments of the legs bear thin flattened plates (oostegites) which enclose a ventral brood pouch, known as a marsupium. The young hatch at a post-larval, prejuvenile stage called a manca which lacks the last pair of legs.

Superorder Peracarida (Calman, 1904)

Caprella sp.

Gnathophausia ingens

Platyarthrus aiasensis

Order IsopodaAs in most crustaceans, the isopod body is divided into three distinct regions: head (= cephalon), thorax, and abdomen (= pleon). In isopods, the first segment of the thorax is fused to the head. The remaining seven free segments (pereonites) of the thorax comprise the pereon; each normally bears a pair of uniramous legs, or pereopods. The pereopods are modified for locomotion and for latching onto prey. In isopods, the abdomen primitively consists of 5 free segments (pleonites) plus a fused 6th pleonite+telson (the pleotelson). Each pleonite bears a pair of biramous pleopods, which are used for swimming and for respiration. Isopods have compound eyes, two pairs of antennae, and four sets of jaws. The first antennae are typically chemosensory; the second antennae are typically tactile structures. The jaws are (anterior to posterior): mandibles, maxillae 1, maxillae 2, maxillipeds. As the name implies, the maxillipeds are actually the highly modified appendages of the fused first thoracic segment.

Sphaeromene polytylotos Armadillidium vulgare Deto echinata

Order Isopoda

Order Amphipoda

No carapace; antennules often biramous; eyes usually sessile; gills on thoracic coxae; second and third thoracic limbs usually prehensile; typically bilaterally compressed body form.

Examples: Orchestia, Hyalella, Gammarus.

Orchestia agilis

Subphylum MyriapodaThe myriapods comprise four classes of multi-legged arthropods with at least 18 legs (9 pairs) in adults. Two of these classes, the Diplopoda (millipedes) and Chilopoda (centipedes) primarily include relatively large-bodied, macroscopic organisms that are readily seen by the general public and are addressed in this website. The other two classes, Symphyla and Pauropoda, which lack common names, are microscopic organisms that are at most only a few mm in length and will not be addressed here. The Diplopoda and Chilopoda are ecologically important classes that occur throughout the temperate and tropical zones of the world and have been unintentionally introduced by man onto most oceanic islands. They are major components of terrestrial ecosystems including even xeric (desert) environments, yet they are poorly known and have been relatively ignored by past and present biologists.

Apheloria virginiensis

Narceus americanus

Class Pauropoda (Lubbock, 1867)

Pauropods are small (less than 5 mm), pale, terrestrial arthropods that are rarely encountered by the casual observer.  Superficially they may resemble insects such as collembolans or psocopterans, but adult pauropods have 11 (or sometimes 12) body segments and 9 (or sometimes 10 or 11) pairs of legs.  They also possess unique forked antennae (see figure below) and a distinctive locomotory pattern characterized by rapid burst of movement and frequent abrupt changes in direction.  Most pauropods lack eyes and a tracheal system. Pauropods can be found in soil, decaying wood, leaf litter, and other moist places, where they feed on fungi and decaying organic matter.  Over 500 species of pauropods have been described so far.

Pauropoda

Pauropus huxleyi

Order Pauropodina

Family Afrauropodidae ()

Family Brachypauropodidae (Silvestri, 1902)

Family Millotauropodidae (Remy, 1950)

Family Pauropodidae (Lubbock, 1867)

Class Diplopoda (de Blainville in Gervais, 1844)

Like centipedes, millipedes have bodies that are made up of numerous segments. The first four thoracic segments each bear a single pair of legs, but the following abdominal segments all have two pairs. Millipedes lack poisonous fangs and do not bite; rather, to discourage predators they roll into a defensive ball and many emit poisonous or foul-smelling substances.Most of the approximately 8000 species of millipedes are herbivores or scavengers, living primarily on decaying plant and animal matter in moist microhabitats. Some species are adept and powerful burrowers. Like centipedes, female millipedes lay eggs in nests, which are often carefully guarded. Newly hatched millipedes usually have only 3 pairs of legs, adding legs and body segments with each molt as they grow.

Class Diplopoda (de Blainville in Gervais, 1844)

Ommatoiulus rutilans

Octoglena anura

Class Diplopoda de Blainville (in Gervais, 1844)

Sigmoria (Falloria) nantahalae Hoffman, 1958

Subclass Penicillata Latreille, 1829

Polyxenus lagurus (Condé 1951)

Commonly known as bristly, pincushion or dwarf millipedes (Blower 1985, Harvey & Yen 1989), Penicillata rarely exceed 4 mm in length and have 11-13 adult body segments and 13-17 pairs of legs (Hoffman 1982). As in other Diplopoda, most segments bear two pairs of walking legs, the antennae have four prominent apical cones and the spermatozoa lack flagella (Enghoff 1984). However, Penicillata differ markedly from other millipedes in a number of ways: the body wall is thin, flexible and uncalcified; the body is adorned with long, stiff, serrate setae arranged in dorsal, lateral and caudal tufts; and sperm transfer is indirect.

Fewer than 100 species of Penicillata have been described worldwide (Hoffman 1982). Bristly millipedes have been collected in many parts of mainland Australia and in Tasmania (Black 1997), but little is known of their taxonomy or biology in this country. The Western Australian species Unixenus mjoebergii has been reported to swarm in large numbers in spinifex country in the Hamersley Range area (Koch 1985). In contrast, an undescribed Tasmanian polyxenid has proved to be highly elusive (Mesibov 2001).

Order Polyxenida (Lucas, 1840)

family Lophoproctidae (Silvestri, 1897)

family Polyxenidae (Lucas, 1840)

family Synxenidae (Silvestri, 1923)

Body has hair-like bristles, especially at the "tail", used to defend themselves from ants (not all have said "bristle tail“).Members are unique in appearance among millipedes and rather small.

Polyxenus lagurus (Condé 1951)

Subclass Chilognatha (Brandt, 1833)

body hard; exoskeleton calcified; setae scattered, never in tufts; males with reproductive appendages, reproduction requiring contact between sexes.

Infraclass Pentozonia

The Pantozonia includes the pill millipides, which are able to roll into co mplete sphere. In this group, the last one or two pairs of legs in the male are enlarged to form telopods or claspers which assist in sperm transfer. Pentazonia refers to the five cuticular components that make up each body ring, i.e. a target arch, two pleurites, and two sternites.

Order Glomeridesmida  Order Sphaerotheriida  Order Glomerida 

Order Glomeridesmida (Cook, 1895)

These are small, rather primitive-looking blind millipídes found in tropical regions.The body is rather flattened and consists of 22 segments. These animals are unables to roll Into balls and are possibly similar to the ancestral millipide.

Glomeridesmus sp. Drawing by R.G. Kuhler.

Order Sphaerotheriida  Pill millipedes are capable of rolling into perfect balls when disturbed. They may sometimes be confused with garden slaters but pill millipedes can tuck their head and legs in so they are entirely concealed, while slaters cannot. Most millipedes are long and slender, but pill millipedes are short and stout with a covering of hard, shiny segments called tergites.Like most millipedes, pill millipedes are herbivorous, feeding on decomposing organic matter on the forest floor or among leaf litter. Besides rolling into a ball, pill millipedes found in the northern hemisphere can also defend themselves with a chemical defence. Along their body are pores that release a smell that can kill or scare off other small creatures. To humans, the smell is similar to almonds, but to small creatures it is extremely toxic as it contains the chemical cyanide.

Sphaerotheriids

Order Glomerida

Glomeris marginata (Villers, 1789)

12 segments, can roll into a perfect ball or sphere.Comprise millipedes that share one unusual feature, the ability to coil into a sphere or “pill”. When coiled, such millipides keep the appendages tucked away, to obvious defensive advantage. Glomerids are also chemically protected, by glands arranged two per segment, with opening along the mid-dorsal line.

Infraclass Helminthomorpha

Elongate, worm-like millipedes with varying degrees of fusion among segmental sclerites; either the anterior or both pairs of legs on segment 7, or the posterior legs on segment 7 and the anterior on segment 8, are modified into copulatory appendages or "gonopods."

Order Siphoniulida (no subterclass named)

Helminthomorpha

Pseudopolydesmus serratus

males unknown; body cylindrical, head prolonged into prominent "beak." Known only from seven females.

Family Siphoniulidae (Pocock, 1894.)

Subterclass Colobognatha (Brandt, 1834)

Order Platydesmida (Cook, 1895)

Gonopods comprised of caudal legs on segment 7 and anterior on segment 8; body generally flattened, tergites with "paranota"; head generally subtriangular.

Family:Andrognathidae (Cope, 1869*)Platydesmidae (DeSaussure, 1860)

Brachycybe rosea

Order Polyzoniida (Cook, 1895)

Gonopods comprised of caudal legs on segment 7 and anterior on segment 8; body arched dorsally, tergites without "paranota" [lateral expansions]; head generally subtriangular.

Bdellozonium cerviculatum (Cook & Loomis, 1928)

Family HirudisomatidaeFamily Polyzoniidae Family Siphonotidae Family Siphonocryptidae

Buzonium crassipes (Cook & Loomis, 1928)

Order Siphonophorida

Family SiphonophoridaeFamily Siphonorhinidae

Gonopods comprised of caudal legs on segment 7 and anterior on segment 8; body relatively narrow, tergites without"paranota"; head prolonged into a variable "beak." Includes the millipedes with the most legs/feet.

Illacme plenipes (Cook & Loomis, 1928)

Subterclass Eugnatha (Attems, 1898)

Superorder Nematophora (Verhoeff, 1913)

The name means ‘thread-bearer’. In Nematophora, the sterna are not fused with the pleura. In this character, Nematophora resembles the superorders mentioned above and differs from those treated further down.

Order Stemmiulida 

Gonopods comprised of anterior legs on segment 7, posterior legs on segment 7 reduced to nonfunctional remnants; body subcylindrical, tapering caudad, head with a pair of large ocelli; caudal end with spinnerets.

Prostemmiulus sp

Order Callipodida 

Gonopods comprised of anterior legs on segment 7; body generally cylindrical and frequently ornamented with ridges and crests, 40-60 segments, caudal end with spinnerets.

Abacion magnum

Family Abacionidae

Family Schizopetalidae

Family Callipodidae

Family Caspiopetalidae

Family Dorypetalidae

Family Sinocallipodidae

Order Chordeumatida

Gonopods comprised of both leg pairs on segment 7; body subcylindrical, tapering caudal, toward tapered end, occasionally with paranota, 26-32 segments, caudal end with spinnerets.

Polymicrodon polydesmoides (Leach, 1814)

Scoterpes copei (Packard, 1881)

About 32 families

Adritylidae Altajellidae Anthroleucosomatidae Apterouridae Attemsiidae Biokoviellidae Brachychaeteumatidae Branneriidae Caseyidae Chaemosomatidae Chordeumatidae Cleidogonidae Conotylidae Craspedosomatidae…

Superorder Juliformia 

Juliformia constitute the millipedes as typically understood by laymen: long, cylindrical animals with plenty of legs (although the highest numbers of legs occur in colobognathans, cf. above). The defence glands of Juliformia produce benzoquinones – a type of defensive chemical which is widely distributed among arthropods.

Schizophyllum sabulosumOmmatoiulus rutilans

Order Julida Gonopods comprised of both leg pairs on segment 7; body generally cylindrical, with conspicuous grooves or striae in two families, 30-90 segments; mostly small to moderate-size millipedes but with the longest species in North America (about 12 cm [6 1/2 inches] long).

Cylindroiulus boleti

Order Spirobolida

Gonopods comprised of both leg pairs on segment 7; body generally smooth and cylindrical, 35-60 segments; mostly moderate-size to large, robust millipedes.

Centrobolus annulatus

Family:AllopocockiidaeAtopetholidaeFloridobolidaeMessicobolidaePachybolidaePseudospirobolellidaeRhinocricidaeSpirobolellidaeSpirobolidaeTrigoniulidaeTyphlobolellidae

Narceus americanus

Order SpirostreptidaGonopods comprised of both leg pairs on segment 7; body generally smooth and cylindrical, 30-90 segments; size varying from narrow, fragile species to huge and robust, including the largest known millipedes (about 28 cm [10 1/2 inches] in length).

12 FAMILIESAdiaphorostreptidaeCambalidaeCambalospidaeChoctellidaeGlyphiulidaeHarpagophoridaeIulomorphidaeOdontopygidaePericambalidaePhysiostreptidaePseudonannolenidaeSpirostreptidaeOrthoporus ornatus (Girard, 1853)

Superorder Merocheta

In most species of Merocheta the body rings (‘segments’) have a pair of keel- or winglike dorsolateral outgrowths, giving the dorsal side a flattened appearance.

Order Polydesmida

Polydesmus collaris

Gonopods comprised of anterior legs on segment 7; body usually with 20 segments, occasionally 19, usually with variable "paranota" that impart a flattened appearance and the name "flat-back millipedes"; dorsum varying from smooth and unmodified to highly ornamented with lobes and pustules; size varying from 3-150 mm [over 6 inches]; large forms often highly colorful, with vivid red, orange, blue, and violet pigmentations in spotted or banded patterns. This order has the most species and is only one with cyanide in defensive secretions.

About 28 families

Ammodesmidae Aphelidesmidae Campodesmidae Chelodesmidae Cryptodesmidae Cyrtodesmidae…

Class ChilopodaCentipedes are uniramian arthropods whose bodies are made up of a chain of many (up to 177) flattened segments, each except the one behind the head and last two bearing a single pair of appendages (legs). The appendages of the first body segment have been modified to form large, poisonous fangs that are used to capture prey. The bite of a large centipede, however, can be painful to an adult and dangerous to a small child.

Centipedes are predatory, feeding on soil invertebrates such as earthworms and terrestrial insects. All centipedes are terrestrial, but they require moist microhabitats. Fertilization is internal, with spermatophore transferred in ways similar to many arachnids. Centipedes lay eggs, which in some species are carefully brooded by the female. When they hatch, the young resemble miniature adults.

This class comprises five orders distinguished by the number of legs and pedal (leg-bearing) segments, and by the degree of "heteronomy" (unequalness) or fusion in the "tergites" (the dorsal segmental plates). The orders are combined into two subclasses based on the position of the "spiracles" (openings to the tracheal or respiratory system) and the general body form.

Class Chilopoda

Scutigera coleoptrata

Scolopendra cingulata

Hemiscolopendra marginata (Say, 1821);

Class Chilopoda

Lithobius variegatus

Order Scutigeromorpha

Subclass Notostigmophora"spriacles" are located middorsally, head is "dome shaped."

Adults with 15 pairs of legs and pedal segments; hatchlings with four; characterized by very long legs and antennae, and fusion of tergites, resulting in less than 15 dorsal plates.

Scutigera coleoptrata

Subclass Pleurostigmophora"spiracles" located laterally, head flattened. Forms exhibit two modes of development - "anamorphic," in which hatchlings possess less than the adult complement of legs and segments, adding legs and segments, and becoming larger, at each molt; and "epimorphic," in which hatchlings possess the full adult complement of legs and segments, and become larger at each molt.

Order Lithobiomorpha

"anamorphic" forms; adults with 15 pairs of legs and pedal segments; hatchlings with 6-8; exhibits strong tergite"heteronomy" with alternating long and short plates.

Henicops maculatus Newport, 1845

Order Craterostigmomorpha

(1 family; also only 1 genus and at most 2 species) - "anamorphic" forms, adults with 15 pairs of legs and pedal segments, hatchlings with 12. eem to represent a transitional stage between the Lithobiomorpha and the Scolopendromorpha. Only one genus (Craterostigma) which is found in Tasmania and New Zealand.  Length 2-5 cm

Craterostigmus tasmanianus (Pocock, 1894)

Order Scolopendromorpha(3 families) - "epimorphic" forms with 21 or 23 pairs of legs and pedal segments, with a low degree of tergite "heteronomy" [segments are more-or-less uniform]. Includes the largest centipedes - the aggressive, intimidating species known to the general public.

Scolopocryptops sexspinosus

Scolopendra subspinipes mutilans

Subclass Epimorpha

Order Geophilomorpha

(11-12 families) - "epimorphic" forms with 29 or more pairs of legs and pedal segments, without tergite "heteronomy." Includes the only centipedes with 100 or more feet/legs.

Necrophloephagus longicornis

Chilopod cladogram, from Edgecombe, G. D. and Giribet, G., 2002

Class Symphyla These tiny myriapods generally resemble very small centipedes.  The creatures are blind and colourless  The mouthparts consist of a pair of mandibles and 2 pairs of maxillae.  There are 12 leg-bearing trunk segments; with 6-7 pairs legs at birth and 12 pairs at maturity.  Tracheal system anterior body only, with a single pair of spiracles on the head.The terminal segment carries a pair of silk-producing spinnerets. Unlike centipedes, there are more tergites than segments.The gonopore is on fourth segment.  The spermatophore is deposited on the ground.  The female collects it and stores it in the mouth.  The egg is taken from gonopore to mouth and coated in sperm.Symphylans are burrowers, living deep in the soil, often aggregated in large numbers (more than 5000 per square metre).   There are about 160 living species.  Length 2-10mm.

Scutigerella immaculata

Myriapod cladogram, from Edgecombe, G. D. and Giribet, G., 2002

Subphylum ChelicerataChelicerate arthropods are an ancient group that includes eurypterids (extinct), horseshoe crabs, spiders, ticks and mites, scorpions, and sea spiders. They are characterized by having six pairs of appendages that include a pair of chelicerae, a pair of pedipalps, and four pairs of walking legs (a pair of chelicerae and five pairs of walking legs in horseshoe crabs).They have no mandibles and no antennae. Most chelicerates suck liquid food from their prey.

Achaearanea tepidariorum

Acanthepeira stellata

Class Arachnida

This large Class of arthropods includes over 60,000 described species (and most likely a very large number of so-far undescribed ones). Spiders make up the majority of these (over 50,000 described species); with mites and ticks next largest (around 48,200 species). The Arachnida also includes a diverse array of smaller groups, including scorpions (1200 species), whip scorpions (100 species), palpigrades (60 species), pseudoscorpions (2000 species), solpugids (900 species), and harvestmen (5000 species). Nearly all species are terrestrial.

Arachnids have a pair of tagmata called a prosoma and opisthosoma. The prosoma is partially or completely covered with a carapace-like shield. The opisthosoma may be segmented or unsegmented. The appendages on the opithosoma are absent or modified, being used as spinnerets (spiders) or pectines (probably sensory in function, found in scorpions). Respiration is via tracheae or book lungs; it is cutaneous in many small arachnids.

Class Arachnida

Class Arachnida

Dermacentor occidentalis

Smeringurus mesaensis

Argiope bruennichi

Order Araneae

Spiders are a large group of 35,000 species, distributed throughout the world. The spider body is compact: a cephalothorax (prosoma) and abdomen (opisthosoma), both unsegmented and joined by a slender pedicel.Anterior appendages are a pair of chelicerae (Figure 18-5), which have terminal fangs through which run ducts from poison glands, and a pair of pedipalps having basal parts with which they chew. Four pairs of walking legs terminate in claws.

Theraphosa blondi

Latrodectus mactans or L. hesperus?

Suborder Opisthothelae

Infraorder Mygalomorphae

Mygalomorph spiders constitute a moderately diverse group including more than 2,600 described species, currently classified into over 300 genera and 15 families.  Familiar mygalomorphs include tarantulas (also called baboon spiders) and trapdoor spiders, but many other distinctive taxonomic groups exist.  Most mygals are relatively large, long-lived (15-30 years), ground dwelling spiders - the largest spiders in the world are in fact mygalomorphs.   These spiders build a diverse array of silk constructs for prey capture, shelter, and protection (Coyle 1986).  Considered an ancient monophyletic group (Coddington & Levi 1991; Platnick & Gertsch 1976; Raven 1985), mygalomorphs retain several characteristics that are considered primitive for spiders (e.g., two pairs of book lungs, simple spinning structures, etc). Many mygalomorph taxa are dispersal-limited and regionally-endemic, and have long been favorites of biogeographers (e.g., Griswold & Ledford 2001; Platnick 1981).  Mygalomorph lineages have a deep evolutionary history, as reflected in a rich fossil fauna that extends back to the lower Triassic (Selden & Gall 1992), with fossil representatives of several families dating to the mid-Cretaceous (see Eskov & Zonshtein 1990; Penney et al. 2003; Selden 2002).  Recent molecular clock analyses suggest intra-familial divergences date to the Cretaceous  (Hendrixson & Bond 2007), and inter-familial divergences may be as old as 300 Ma (Ayoub et al. 2007).

Infraorder Mygalomorphae

Calisoga longitarsus

Bothriocyrtum californicum

Psalmopoeus irminia

Family Cyrtaucheniidae

Aptostichus simus

Family Actinopodidae

Missulena bradleyi

Family Barychelidae

Ozycrypta sp

Family Hexathelidae

Macrothele calpeiana

Infraorder Araneomorphae

Leucauge venusta Hypochilus pococki

Family HypochilidaeThe Lampshade spiders of the family Hypochilidae are among the most primitive of araneomorph spiders. There are two genera and eleven species currently recognized. Like mygalomorph, hypochilids have two pairs of book lungs, but like araneomorphs they have intersecting fangs. These long-legged spiders build typical "lampshade" style webs under overhangs and in caves. The Hypochilidae are a sister clade to the Neocribellatae, which contain all other spider species in the Araneomorph (Coddington & Levi, 1991, p576).

Hypochilus pococki

Serie Haplogynae

Pholcus phalangioides

Dysdera erythrina

Serie Entelegynae

Misumena vatia

Dolomedes tenebrosus Leucauge magnifica

Order AcariThe Acari can be defined by the following characteristics:

•Hexapod prelarva (lost in Parasitiformes and many derived Acariformes) •Hexapod larval stage •Three octopod nymphal stages (variously abbreviated in derived taxa) •Gnathosoma delimited by a circumcapitular suture •Palpcoxal endites fused medially forming a hypostome •Hypostome with rutella or corniculi (lost in many derived Acariformes) •Loss of external evidence of opisthosomal segmentation, i.e. without tergites or sternites •Ingestion of particulate food (lost in many derived taxa)

Order Acari

Neotrichozetes (top), Dendrolaelaspis (bottom) Limnesia

AcariformesA number of developmental characteristics unite the Acariformes. Development is anamorphic, meaning that body segments are added between moults. Also, prior to moulting, the legs of the subsequent instar are formed within the body rather than within the hulls of the previous instar's legs. There are also several characteristics of acariform setae that differentiate them from other Acari. Another name for the Acariformes is the 'Actinotrichida', which refers to the fact that their setae have a layer of optically active chitin, 'actinochitin', that is birefringent under polarized light. Other mites - the Parasitiformes and Opilioacariformes - lack actinochitin and are sometimes grouped as the 'Anactinotrichida'. Trichobothria, specialized setae that are sensitive to vibrations and air currents, are found in the Acariformes but not in other mites. Other modified sensory setae unique to the Acariformes include solenidia and eupathidia. Lindquist (1984) provides a list of the apomorphic characters of this group.

Meristolohmannia

Trombidiformes

According to OConnor (1984), the Trombidiformes are characterized by several charcters that unite the Prostigmata (which makes up the majority of the group) with the Sphaerolychidae and Lordalychidae. These characters are: anamorphic segments AN and PA not added in ontogeny; hysterosomal segment C with fewer than four pairs of setae; and hysterosomal segments D and E with fewer than two pairs of setae. OConnor's cladogram also indicates that the character 'hysterosoma without primary segmentation' is a feature of the Trombidiformes; however, as it also occurs in a number of sarcoptiform taxa, it is not a unique character. Lindquist (1996) notes that most (but not all) members of the Trombidiformes can be differentiated from the Sarcoptiformes by having chelicerae with a hooklike or styletlike movable digit rather than the ancestral chelate form. Likewise, many trombidiform mites have a padlike or rayed median empodium in contrast to the clawlike or disk-shaped empodium of sarcoptiforms. Within the Trombidiformes, the Prostigmata are united by having the stigmatal openings to the tracheal system located anteriorly (e.g. on the prodorsum or near the base of the mouthparts).

Cunaxa (Cunaxidae) feeding on a springtail (Collembola)

Parasitengona

The Cohort Parasitengona comprises 6 superfamilies of terrestrial prostigmatan mites and 9 superfamilies of aquatic mites (this group being termed the Hydracarina or water mites) for a total of about 60 families. There are about 7000 named species, 5000 of which belong to the Hydracarina (Welbourn 1991). Many of the named terrestrial species belong to the medically important Trombiculoidea, a group that contains the chiggers (also known as scrub itch mites).The major uniting characteristic of the Parasitengona is their complex life-cycle, consisting of a parasitic larva, two inactive pupa-like stages that represent the protonymph and tritonymph, and active predatory deutonymphal and adult stages.

Parasitengone larva parasitizing a parasitengone adult (Smarididae) from Queensland, Australia.

Hydracarina

Members of the Hydracarina are most obviously separated from other taxa in the Cohort Parasitengona by having nymphal and adult stages that live beneath the surface of the water. Morphological characteristics that differentiate the group are less obvious. The combination of larval characters unique to the Hydracarina is that larvae lack the supracoxal seta 'e', the companion seta associated with phi and omega on leg I, and the companion seta associated with the dorsal eupathidium on tarsus I. As well, the palpal genu has two setae compared to the one seta found in larvae of other Parasitengona (Welbourn 1991). Witte (1991) lists a number of unifying postlarval characters, including: presence of glandularia (a combination of seta and gland), reduction of acrosomal filament of the sperm cell, and modifications of the posterior arms of the ejaculatory complex (the complex group of internal sclerites used by the male to form the spermatophore). However, as Harvey (1998) points out, it isn't clear whether Witte intended the Stygothrombidioidea to be included in the Hydracarina.

Hydrodroma (Hydrodromidae, Hydryphantoidea) from Queensland, Australia.

Order Parasitiformes

Parasitiform mites have free coxae, a ventral anal opening covered by a pair of plates, corniculli on the hypostome (lost in ticks), a sclerotised ring surrounding the gnathosoma (capitulum), and usually a biflagellate tritosternum (lost in ticks, many holothyrids, and some parasitic Mesostigmata).

Allothyrus sp.

Suborder Ixodida According to Lehtinen (1991) the following characters are synapomorphic for the Ixodida:

1.latigynial plates reduced; 2.palpal tarsus reduced;3.hypostome projecting and sawlike.

Other prominent features of ticks are their large size, when compared to other mites, and Haller's organ, a complex sensory apparatus on tarsus 1 (the holothyridan mites have a homologous organ).

Haemaphysalis bremneri mouthparts, showing toothed, sawlike hypostome.

Otobius megnini

Amblyomma hebraeum

Order ScorpionidaScorpions are easily distinguished from other arachnids by their large, well developed claws (pedipalps) and distinct division of the abdomen (opisthosoma) into a broad preabdomen (mesosoma) and narrow, tail-like postabdomen (metasoma). All scorpions possess a poisonous sting (telson) and a pair of peculiar, comb-like, sensory appendages called pectens. There about 1100 species of scorpions known worldwide, and probably that many more still to be discovered. Although they are normally associated with hot, dry areas like deserts, scorpions are found in a variety of habitats including cool, wet forests and grasslands. Scorpions are among the oldest arachnids. The earliest fossils date from the middle Silurian rocks, over 400 million years old. Early scorpions had large compound eyes, but were otherwise similar to living forms. Scorpions are generally large arachnids. Adults range in size from 1.5 cm to 21 cm in length. Some fossil scorpions are thought to have been up to 1 meter in length! All are predatory. Their prey includes a variety of arthropods and other invertebrates, and the larger species are known to prey on small vertebrates. The scorpion's most notorious feature is its poisonous sting. While all scorpions are venomous, only about twenty species worldwide possess venom of sufficient toxicity to kill humans.

Order Scorpionida

Cyclophthalmus senior

Suborder Scorpiones

Centruroides vittatus

Order Solifugae (Sundevall, 1833)

Solifugae is an order of Arachnida, containing more than 1,000 described species in about 140 genera. The order is also known by the names Solpugida, Solpugides, Solpugae, Galeodea and Mycetophorae. Their common names include camel spider, wind scorpion, jerrymuglum, sun scorpion and sun spider. In southern Africa they are known by a host of names including red romans, haarskeerders and baarskeerders, the latter two relating to the belief they use their formidable jaws to clip hair from humans and animals to line their subterranean nests.Solifugae are not true spiders, which are from a different order, Aranea. Like scorpions and harvestmen they belong to a distinct arachnid order.

Eremochelis bilobatus (Muma)

AmmotrechidaeCeromidaeDaesiidaeEremobatidaeGaleodidaeGylippidaeHexisopodidae

Family Ammotrechidae (Roewer, 1934)

Ammotrechidae are a family of solifuges distributed in the Americas and the Caribbean island. They include 22 described genera and at least 83 species. Members of this family can be distinguished from members of other families by the absence of claws on tarsi of leg I, tarsal segmentation 1-2-2-(2-4), pedipalps with pairs of lateroventral spines, and by males having an immovable flagellum on the mesal face of each chelicerum. The propeltidium of Ammotrechidae is recurved (Roewer, 1934).

Ammotrechula pilosa Muma

Class EurypteridaThe Eurypterida are an extinct Paleozoic group of chelicerate arthropods of which 200 fossil species are known.  These were spectacular animals, although very rare as fossils.  The largest, such as Pterygotus; reached 2 meters and more in length, but most species were less than 20 cm.  Although called "sea scorpions" only the earliest ones were marine.  Most lived in brackish water, sheltered lagoons etc.  Many species inhabited shallow aquatic environments and some may have been amphibious, emerging onto land for at least part of their life cycle.  They may have been capable of breathing both in water and in air.  Their morphology suggests that they fed on a variety of kinds of foods.  Some forms like Mixopterus were very scorpion-like and may have even been ancestral to scorpions.  About two dozen families of eurypterids are known.

Dolichopterus macrocheirus

Suborder Eurypterina

Superfamily Eurypteracea

This superfamily includes the "typical" (unmodified) Eurypterids, in which the last prosomal appendages developed as swimming legs that carry paddles formed by expansion of the two penultimate joints. They can be considered the ancestral lineage from which the other groups evolved.

Baltoeurypterus tetragonophthalmus

Superfamily MixopteraceaThe most scorpion-like of the Eurypterids (and possibly ancestral to the scorpions), this is a diverse group of often spiny Eurypterids. Many of these animals were clearly amphibious, as is indicated by a trail in the Silurian of Ringerike, Norway, believed to have been made by a large Mixopterus.

Megalograptus ohioensis

family Megalograptidae(Caster & Kjellesvig-Waeritag, 1955 )

family Carcinosomatidae(Størmer 1934 )

Carcinosoma scorpionis

Family Mycteropidae(Størmer, 1951)

Mycterops? scabrosus

Suborder PterygotinaThe Pterygotids are among the most spectacular of the eurypterids, in the more advanced forms equipped with large chelicerae or "pincers".  In most eurypterids, the chelicerae are rather small; only in the Pterygotina do they grow into large pincer-type grasping organs as those shown here.  But despite their resemblance, these chelicerae are not homologous to the pincers of scorpions (i.e. they are not formed from the same pair of limbs).  Scorpion pincers are the second pair of appendages, whereas pterygotid pincers are the first.  These animals were active hunting by site predators, as indicated by the large bulbous eyes, located at the side (rather than the middle) of the head, giving superior peripheral vision.As with most Eurypterid lineages, the Pterygotina reached their acme in the late Silurian and early Devonian, at the time the great deltas of Euramerica and else where were creating a rich near-shore detritus-based food-chain that enabled the armoured ostracoderms and many other prey-animals to flourish.

Pterygotus (Acutiramus) buffaloenisis

family Slimoniidae family Pterygotidae(Clarke & Ruedemann, 1912 )

Pterygotus (Pterygotus) rhenaniae

family Jaekelopteridae

Jaekelopterus

Slimonia acuminata Salter 1856

Order Stylonurina Suborder Hibbertopterina

The Hibbertopterina were mostly large animals, many of which may have ventured onto land, flourishing in the moist Permo-Carboniferous coal swamps.   The outer surface of the skin is armed with spiny scales.  The prosoma is subsemicircular, strongly convex; the compound eyes almost in the middle of the head ("subcentral"), with inflated angular lobes between them.  The abdominal tergites are convex.  The posterior (last) prosomal legs have a basal extension, which is a distinguishing mark of the group.

Hibbertopterus scouleri

family Hibbertopteridae (Caster & Kjellesvig Waering, 1955 )

Campylocephalus

Hibbertopterus

Class XiphosuraThere are only 3 genera and 5 species of Xiphosura left alive today, but they were much more numerous and diverse during the Paleozoic era.  The surviving horseshoe crabs (Limulus) are 'living fossils', barely changed in some 250 million years (since early Triasssic time).  Members of this class have a large shield that covers the cephalothorax; the carapace is hinged between the cephalothorax and abdomen.  The exoskeleton generally consists of three parts, the large, semicircular cephalothorax, or prosoma, the usually smaller, subtriangular and in earlier forms "trilobite"-like opisthosoma, and the long stout tail-spine or telson (which is actually the end part of the opisthosoma).

The prosoma contains both head and visceral organs. The compound eyes are small (and absent in some early forms), and there are six pairs of legs (in the living Limulus) but no antennae.  The second pair of appendages, the pedipalps, resemble walking legs. Respiration is via 5 pairs of book gills, the flaps of which beat in a metachronal rhythm to produce a vigorous current.  Recent xiphosurids (Horseshoe crabs) feed on worms and other small invertebrates.  They are often used as laboratory animals by physiologists.  It has been argued that because of their unique status as prehistoric "living fossils" they deserve special conservation status.

Class Xiphosura

Pseudoniscus roosevelti

Order SynziphosuridaThe Synziohosurida are a small, fairly diverse, paraphyletic / ancestral group of primitive Xiphosura. Rather trilobite-like in appearance.  Large prosoma (headshield), simple eyes only. 9 or 10 opisthosomal (abdominal) segments, most or all of which are free (unfused).  The segments are not chelate.  Mostly brackish or freshwater environments, although some forms were marine (marginal marine?).  Usually found in association with eurypterids and ostracoderms.

Cyamocephalus loganensis Currie 1927

Family Weinberginidae (Richter and Richter, 1929)

Weinbergina opitzi (Richter and Richter, 1929)

Family Bunodidae (Packard 1886)

Small elongate forms, ornamented prosoma, abdomen with broad axis, 9 free segments, post-abdomen with 3 or 4 segments. 

Family Limuloididae (Størmer, 1952)

Limuloides limuloides Woodward, 1865

Family Bunodidae (Packard 1886)

Bunodes lunula Eichwald, 1854

Family Pseudoniscidae Packard 1886

Cyamocephalus loganensis Currie, 1927

Family Kasibelinuridae Pickett, 1993

Kasibelinurus amicorum Pickett, 1993

The Order Xiphosurida/Limulida includes most Xiphosura, and all post-Devonian forms. These animals were quite common during the Carboniferous, and some forms seem to have been amphibious, although other types (e.g. Paleolimulus) were fully marine. Beginning from small ancestral types they increased in size through the Mesozoic and Cenozoic, and modern horseshoe crabs are giants compared to Paleozoic forms (the horse also has shown a similira tendency to increase in size but reduce in diversity throughout the Tertiary and Quaternary periods), There is the tendency towards fusion of the opisthosomal tergites (free abdominal segments) to form a thoracetron or fused plate. There are several superfamilies and a greater number of families, but only one lineage made it into the post-Paleozoic world. Cladistic analysis so far indicates that the Xiphosurida are a monophyletic taxon.

Order Xiphosurida

Liomesaspis laevis Raymond 1944

Suborder BellinurinaAnderson and Selden consider the Bellinuroidea a suborder (Bellinurina) which contains only two families, the Bellinuridae and the Euproopidae. His Euproopidae would seem to be equivalent to the Treatise's Euproopacea, as it includes the genera Euproops and Liomesaspsis (usually each put in a seperate family of the Euproopacea). These were small animals, with short bodies, only partially fused abdominal segments, and wide rounded horseshoecrab-like headshields, giving them a rather trilobite-like resemblence, apart from the long tail-spine or telson. They frequented the coal swamps and were in all likelihood amphibious, perhaps living part of their life-cycle on land. 

Family Euproopidae Eller, 1938 (junior synonym: family Liomesaspidae Raymond 1944

Euproops danae Meek and Worthen, 1865Liomesaspis laevis Raymond, 1944

Family Bellinuridae (Zittel and Eastman, 1913 )

Bellinurus trilobitoides Buckland, 1837.

The most primitive Xiphosurid family, evolving from a Kasibelinurus-like ancestor, representing an ancestral type from which more advanced forms may have developed. The forward abdominal segments are free, but the last two or more rear ones may be fused. This fusing of the abdominal segments is a common and defining tendency among the Xiphosurida.

The Limulina represent the most advanced lineage of the group, descended from early Carboniferous transitional forms like Rolfeia.  The cephalothorax is wide and arched, with the cardiophthalmic region poorly defined. .  The abdominal segments are usually fully fused, although the marginal spines are movable. Includes the 5 living species of "horseshoe crabs" (Limulus).  These creatures live in a shallow marine environment (although some Paleozoic forms may have been brackish water inhabitants).  Jurassic Xiphosurids are extremely similar to those found today.Anderson and Selden distinguish between the superfamily Paleolimuloidea - defined by the pyramidal cheek node on the carapace - and the superfamily Limuloidea (which Includes all Mesozoic and Cenozoic Xiphosura). 

Suborder Limulina

Superfamily Limuloidea Zittel 1885

Family Rolfeiidae (Selden and Siveter, 1987)

Rolfeia fouldenensis (Waterston, 1985)

Family Paleolimulidae (Raymond, 1944)

Paleolimulus avitus Dunbar, 1923

Family Moravuridae (Pribyl, 1967)

Xaniopyramis linseyi (Siveter and Selden, 1987)

Probably a branch of the Paleolimulidae

Class Pycnogonida Pycnogonids, or "sea spiders", are among the most bizarre-looking arthropods. Another name sometimes used for them, Pantopoda, means "all legs" and describes them perfectly. Pycnogonids have extremely reduced bodies in which the abdomen has almost disappeared, while the legs are long and clawed. The head has a long proboscis with an unusual terminal mouth and several simple eyes on a central tubercle. The head also bears a pair of claws and a pair of ovigers on which the eggs are carried. All in all, it can be hard to tell just which end of a pycnogonid is the head; in this picture the head is to the right (we think) and the proboscis has been bent under the body.

Pycnogonids feed on soft-bodied invertebrates, in particular cnidarians, sucking at them with their probosces, and larval pycnogonids often live as parasites within cnidarian tissues. The intestine of pycnogonids has extremely long diverticulae (blind pouches) that extend to the ends of the legs.

Class Pycnogonida

Pycnogonum stearnsi

Nymphon gracile

Order Pantopoda

Ammothea verenae (Child, 1987.)

Sea spiders, also called Pantopoda or pycnogonids ('pycnogonid' = Greek for 'thick knee') , are marine arthropods of class Pycnogonida. Sea spiders have long legs in contrast to a small body size. The number of walking legs is usually eight (four pairs), but species with five and six pairs exist. Because of their small size and slender body and legs, no respiratory system is necessary, with gases moving by diffusion. A proboscis allows them to suck nutrients from soft-bodied invertebrates, and their digestive tract has diverticula extending into the legs.

The order Pentopoda consists of approximately 1000 species, which are normally split into eighty-six genera. The correct taxonomy within the group is uncertain, and it appears that no agreed list of orders exists.

The trilobites are an extinct group of arthropods that lived in the seas of the world for about 380 million years, from the Precambrian 610 MYA (million years ago) to around the end of the Permian 230 MYA.

The basic trilobite body consists of three sections; a head called a cephalon, a thorax and a pygidium. the head was protected by a single large plate of exoskeleton (chitin) called a cephalic shield. this was originally derived from 5 (in most species) smaller plates which have become fused together. The thorax is composed of a series of practically identical segments enclosed in a series of plates. These plates, one per segment, overlapped posteriorly (towards the back of the animal) like tiles on the roof of a house. This arrangement allows the animal some freedom of movement, and many trilobites were capable of rolling themselves up into a ball much like modern day woodlice, or pill-millipedes. The pygidium is the tail end of the animal, like the cephalon it is comprised of several fused plates, generally it was smaller than the cephalon.

The thoracic segments all have two grooves running across (from front to back), the combined effect of these is to make the animal look as if it has its thorax divided into 3 longitudinal sections. It is this that gives the animals their name, tri for three and lobita from lobe hence tri-lobite = three-lobed.

Subphylum Trilobites

Subphylum Trilobites

Triarthrus Lichas Paradoxides Orders•Agnostida •Redlichiida •Corynexochida •Ptychopariida •Phacopida •Proetida •Lichida •Asaphida

Class: Trilobita (Cambrian-Permian)

Marine arthropods with segmented, largely calcitic skeletons, divided into 3 longitudinal lobes and with cephalon, thorax and pygidium. From 2-4- thoracic segments, each with axis and pleura. Pygidium variable in size. Ventral appendages biramous, and one per segment. 8 major orders:

Order: Redlichiida (L. - M. Cambrian) (eg Paradoxides)

Large semicircular cephalon with strong genal spines, numerous spiny thoracic segments and a tiny pygidium. Eyes large.

Order Agnostida (L. Cambrian - U. Ordovician) (eg Agnostus)

Small trilobites with subequal cephalon and pygidium, usually blind and sutureless. Thoracic segments number only two or three.

Order Corynexochida (L. Cambrian - M. Devonian) (eg Olenoides)

Heterogenous group. Glabella of varied form, sutures opisthoparian, thorax with 7-8 segments, often isopygous.

Order Lichida (M. Cambrian - M. Devonian) (eg Acidaspis)

Usually spiny trilobites, often very large with distinctive cephala and pygidia. Cephalon with broad glabella and opisthoparian sutures. Pygidium often larger than cephalon.

Paradoxides

Olenoides

Agnostus

Lichas

Order Phacopida (L. Ordovician – U. Devonian) (eg Dalmanites, Phacops, Calymene)

Large order of proparian trilobites divided into 3 suborders: Cheirurina, Calymenina & Phacopina.

Order Ptychopariida (L. Cambrian – U. Devonian) (eg Olenus, Harpes)

Large order including the common suborder Olenida with a simple, forward tapering glabella, large thorax and small pygidium.

Order Asaphida (U. Cambrian – Silurian) (eg Asaphus, Trinucleus)

Median ventral suture present, usually macropygous.

Order Proetida (Ordovician – Permian) (eg Phillipsia)

Glabella large and vaulted, usually with genal spines, opisthoparian suture. Thorax with 8-10 segments. Isopygous. Pygidium usually furrowed and not spiny.

Dalmanites Phacops

Trinucleus Phillipsia

Trilobite classification and geological ranges

Este trabajo cuenta con una amplia descripción de las diferentes categorías taxonómicas agrupadas dentro del filum artrópoda. Información tomada de bases de datos y libros de zoología.

Prohibida de reproducción y propagación sin consentimiento del autor.