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Mollusca & Annelida
ANCESTRALPROTIST
Porifera
Ctenophora
Cnidaria
Acoela
True Tissues
Metazo
a
Eu
metazo
a
Bilateria
Hemichordata
Echinodermata
Chordata
Platyhelminthes
Rotifera
Ectoprocta
Brachiopoda
Mollusca
Annelida
Nematoda
Arthropoda
Deu
tero
stom
ia
Lo
ph
otro
cho
zoa
Ecd
ysozo
a
Single common animal ancestor
prot
osto
mes
inve
rteb
rate
s
Bilateral & 3 germ layers
Mollusca Body Plan
• Ceolomates (true coelum)– Often very reduced/small
• 3 main body parts– Muscular foot (for movement)– Visceral mass (w/ most internal organs)– Mantle
• Creates calcium based shell• mantle cavity in some (containing gills, anus, and pores)
– Shell in most• Protection against predation & dessication
Mollusk organ systems
Feeding & Digestive:• Many feed with a rasp-like strap called the radula• Herbivores or predators• Filter feeders (using gills or “tentacles”)• Beak (cephalopods)• Complete digestive system w/ specialized organs
– Digestive gland (a.k.a. hepatopancrease)
Cardiovascular:• Open (except in cephalopods)• Hemocyanin
Excretory and osmoregulation• Metanephridia
Mollusk organ systems
Nervous:• “brain” encircling pharynx• Two ventral nerve cords (in most)
Respiratory:• Gills• mantle
Reproductive• Most are dioecious w/ gonads in visceral mass• Many gastropods are hermaphrodites • Typically a ciliated larvae known as the trochophore
Metanephridium HeartVisceral
mass
Coelom IntestineGonads
Mantle
Mantlecavity
Anus
Gill
Foot Nervecords
EsophagusMouth
Mouth
Radula
Radula
ShellStomach
Digestive tract
Generic Mollusc Body Plan
radula
• Four of the major classes of molluscs are– Polyplacophora (chitons)– Gastropoda (snails and slugs)– Bivalvia (clams, oysters, and other bivalves)– Cephalopoda (squids, octopuses, cuttlefish, and
chambered nautiluses)
Polyplacaphora (Chitons)
Chitons
• Oval shaped body• 8 dorsal plates– Unsegmented body
• Foot acts as suction cup to hold in place (to prevent dislodgement and drying)
• Herbivores– use radula to scrap algae off rocks
• Adaptation to intertidal zone
Gastropods (snails & slugs)
(a) A land snail
(b) A sea slug (nudibranch)
Gastropods
• ¾ of all mollusc species• Move by rippling foot or cilia• Shell, reduced, abscent• Torsion • Most are herbivores using radula to eat• Some predator (radula bores holes or shreds prey)• Many w/ eyes at tip of tentacles• Aquatic gills for gas exchange• Terrestrial lining of mantle in mantle cavity for gas exchange
Bivalvia (bivalves/ “shellfish”)
Bivalves• All aquatic• Dorsally hinged 2-part shell
– Adductor muscle holds shell closed• No distinct head• Radula has been lost• Some have eyes and sensory tentacles along the out edge of mantle• Gill in mantel cavity• Gill for filter feeding and gas exchange
– Most are suspension feeders– Cilia move food in gills to mouth
• Incurrent siphon in, excurrent siphon out• Many are sedentary
– Some fix themselves substrates, some move w/ feet
Figure 33.19Mantle
Digestivegland
Hinge areaGut
Coelom
Heart Adductor muscle(one of two)
Anus
Excurrentsiphon
Waterflow
IncurrentsiphonGillGonad
Mantlecavity
Foot
Palp
Shell
Mouth
Figure 33.20Squid
Octopus
Chamberednautilus
Cephalopods
Cephalopods:Octupus, squid, nautilus, cuttlefish
• marine predators• Modified foot
– Tentacles (for prey capture)– Excurrent siphon
• Beak (some with teeth)– Radula reduced or vestigal– Some poisonous
• Move with jet of water out excurrent siphon• Shell is reduces and often internal (except nautilus)• closed circulatory system• Complex brain, eyes, and other sensory organs• Well developed nervous system and senses (e.g., eyes & big brain)
Annelida:segmented worms
• Segmented• Divided by septa internally• Marine, freshwater, and damp soil (terrestrial)
BODY PLAN• Long, thin worm• Coelomates• Segmented
Systems
• Closed cardiovascular system• Complete digestive system w/ specialization• Metanephridia• Gills, parapodia, or surface gas exchange• “brain” near pharynx• Ventral nerve cord
Historical Classes
• Polychaetes• Oligochaeates• Hirudinae
Modern relationship:polycheates > oligochaetes > hirudinae
Polycheata:polycheates and tube worms
Parapodia
Polycheates• Marine• Mobile forms are:– Predators – Herbivores (of large algae)– Scavengers
• Parapodia w/ chaetae (“bristles”)• Movement• Can be vascular and used for gas exchange• Well developed jaws and sensory organs
Polycheates: tube worms• Filter feeders• Gills or “tentacles”
Oligocheates• Aquatic and terrestrial• Setae• Circular and longitudinal muscles• Hydrostatic skeleton• Peristalsis• Gas exchange over surface• Cross fertilizing hermaphrodites
Figure 33.25Epidermis Cuticle
Coelom
Septum (partitionbetween segments)
Metanephridium
Anus
Skin
Metanephridium
Intestine
Gizzard
Ventral nerve cordsCirculatory system vessels
Subpharyngealganglion
MouthCerebral ganglia
Pharynx
Giant Australian earthworm
EsophagusCrop
ClitellumNephrostome
Fusednerve cords
Ventral vessel
Intestine
Chaetae
Dorsalvessel
Longitudinal muscle
Circular muscle
Figure 33.25aAnus
Skin
Metanephridium
Intestine
Gizzard
Ventral nerve cordsCirculatory system vessels
Subpharyngealganglion
Mouth
Cerebral ganglia
PharynxEsophagus
Crop
Clitellum
Figure 33.25bEpidermis Cuticle Coelom
Septum (partitionbetween segments)
Metanephridium
Nephrostome Fusednerve cords
Ventral vessel
Intestine
Chaetae
Dorsalvessel
Longitudinal muscle
Circular muscle
Hirudinae
Hirudinae (leeches)predators, scavengers, blood-sucking parasites
• Mostly freshwater• Lack setae• Dorso-ventrally flattened• Suckers to hold prey• Subtle segmentation• Blood sucking type– bladelike jaws– aneasthetic saliva– anticoagulant, hirudin– Blood letting v. modern use
Circulatory Systems: open v. closed
Respiratory Structures
nephridiostome
nephridiophore