Invertebrate Animals

Second year Students

Dr. Hamza Ahmad Elshabaka

Professor of Embryology

By

Department of Zoology

Phylum: Mollusca

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Hamzashabaka @ gmail.com

General characters:

1-These are bilateral symmetrical and unsegmented

invertebrates.

2- Molluscs are mostly marine and some of them live in

fresh water or on land.

3-They are either unisexual or hermaphrodite animals.

4-They have a fleshy mantle that secretes the calcareous

shell.

5- Most of these invertebrates possess a broad flat

muscular foot for locomotion.

6- Most molluscs have a radula used for scraping off food

materials (bivalves do not possess radula).

7- Most of molluscs have an open circulatory system

with a dorsal pumping heart.

8-They have a fleshy mantle that in most cases secretes

the calcareous shell.

Phylum: Mollusca

I-Class: Polyplacophora

Acanthochiton spinigera

Phylum: Mollusca

Dorsal view Ventral view

General characters

1- Chitons are unsegmented , bilateral symmetric, dorsoventrally

flattened, and show eight dorsal calcareous plates.

2- Chitons have a large and fleshy foot and a separated head, with a

centrally laying mouth opening.

3- The head has no eyes and no tentacles.

4- There is one row of short ctenidia in the mantle groove on each

side of the foot.

Shell plates

Mantle edge

foot

Mouth

head

ctenidia

(The Chiton)

General characters

It is formed of a long horny membrane

with numerous recurved teeth arranged in

successive transverse rows.

Radula of Acanthochiton

T.S of Acanthochiton

Gonad Gut Digestive gland Mantle grooveCtennidium

Foot

Mantle edge

General characters

1- The body is covered dorsally

by the shell.

2- The mantle edge contains

numerous spicules.

3- The mantle groove enclosing ctenidia.

4- The foot is bulky and ventrally located.

5- The viscera include gut, digestive

gland and gonad.

Central teeth

Marginal teeth

Lateral teeth

II-Class: Scaphopoda

Dentalium sp.

(Shell)

General characters

1- The shells are tubular, slightly curved and

in a planispiral way and demarcated externally by

longitudinal projecting ribs.

2-They are usually whitish or yellowish in colour.

3- They are hollow and open at both ends.

4- The opening at the larger end is the main aperture

from which the foot and head project downward.

The smaller opening is known as the apical

aperture.

(The Elephant-tusk)

III-Class: Gastropoda

A-Subclass: Prosobranchiata

1-Order: Monotocardia

Lanistes carinatus

Shell

General characters1- Fresh water molluscs which able

to perform both aquatic and aerial

respiration.

2- The shell is large and the colour is

browinsh with buffy bands.

3-The shell is globose in shape and

sinistral.

Body whorl

Shell aperture

apex

Anterior opening

Posterior opening

Murex tribulusGeneral characters

1- The shell is white in

colour and spirally coiled

(dextral).

2- The shell bears numerous

ribs, spines and raised knobs.

3- The peristome is produced

into a long spout-like shell

siphon.

Body whorl

aperture

siphon

ShellShell

2-Order: Diotocardia

Patella tarentina

Shell

General characters1-The shell is almost conical in shape.

2-The shell is sculptured with dense ribs

radiating out from the apex and very thin

concentric growth circles.

3-The edge of the shell is finely indented.

4-The color is yellow - white with red - brown

rays.

(The Limpet)

Murex angulifer

Spines

ribs

Soft parts of Patella (D.V.)

Visceral

hump

Shell

muscele

mantle

General characters

1- The head is small and distinct from

the foot.

2- The visceral mass is encircled by a horse-

shoe-shaped shell muscle except the

anterior part.

3- The mantle is a flap extending all round the

body and lining the marginal part of the

shell.

Ventral view of Patella

General characters1- The body is composed of a small head,

foot and mantle.

2- The head is small and bears mouth, 2 long

tentacles and 2 eyes.

3- The foot is flattened and ovoid in shape.

4- The mantle is a continuous flap extending all

round the body and the marginal part of the

shell.

Head

Foot

mouth

Shell

B-Subclass: Opithobranchiata

1-Order: Nudibranchiata

Hexabranchus sanguineus

anus

Dorsal view

tentacle head

General characters

1- The body is bilaterally

symmetrical externally.

2- It has no shell and the mantle

covers the whole dorsal surface

and there is no mantle cavity.

3- The foot is large, elongated and

lies on the ventral surface.

2-Order: Tectibranchiata

Aplysia argus

(The Sea Hare)

Tentacle Anus Anal funnel parapodia

Dorsal view

General characters

1- The body is composed of

head, foot and mantle.

2- The head bears mouth opening, 2 eyes

and 2 pairs of tentacles.

3- The foot is a large, elongated muscular

structure and pointed behind.

4- There are 2 fleshy flaps; the parapodia

arise from the postero-dorsal sides of the foot.

5-The mantle is reflected all over the

shell and inside the mantle cavity

there is a single ctenidium.

Foot

C-Subclass: Pulmonata

1-Order: Stylommatophora

Eremina desertorum

V.S. of the shell

Shell

General characters

1-The shell is globose, dextral and milky white in colour.

2-The whorls are four and increase in size towards the

aperture. The last and largest whorl is termed the body whorl.

3- The spire (total whorls except the body whorl) is short.

General characters

1- In V.S. The shell consists of a columella

which is the central axis which is formed by the

coalescence of the inner walls of the whorls.

2- The columella is hollow and ends on the lower side

by a closed umbilicus.

Body

whorl

columella

apex

aperture

Visceral mass

(dorsal view)

headfoot

Digestive gland

rectum

Albumen gland

stomach

Kidney

General characters

The structures appeared in the soft parts

are, the headfoot, the triangular kidney, the

digestive and albumen glands, the stomach

and the rectum

(The Desert Snail)Spire

Shell aperture

S. Of hermaphrodite gland of Eremina

General characters

1- The gland consists of large number

of acini each has a thin wall of germinal

epithelium resting on a basement membrane

and encloses a lumen.

2- Inside the acini, the epithelium forms the

different stages of spermatogenesis and

oogenesis.

Cepaea

Shell

General characters1- Cepaea is a land and air-breathing

snail.

2- The colour of the shell is reddish browen

with dark brown bands.

3- The apertural lip is purple brown in colour.

4- The umbilicus is narrow and the surface

of the snail is semiglossus and has

about 5 whorls.

Arion vulgaris

Whole

General characters1- Slug-like body of a reticulate

texture dorsally.

2- The shell is reduced to a simple

calcareous granules below the

sheiled like mantle coverying the

anterior body.

3- The mantle is located just

behind the head

Head Mantle Tail

foot

Tentacle

Mature

ovum

Spermatogonia

Acini

Spermatozoa

Spermatocytes Spermatids

Connective tissue

2-Order: Basommatophora

Bulinus truncatus

Biomphalaria alexandrina

Limnaea natalensis

Shell

Shell

Shell

General characters

1- Lymnaea natalensis is a

freshwater snail.

2- The upper whorls of the shell are

pointed.

3- The shell is dextral and

brown in colour.

General characters:

1- The Bulinus truncatus is a fresh

water snail with a sinistral shell.

2- The shell has a very large body

whorl and a small spine.

3-The colour varies from yellowish

to dark brown.

General characters

1- Biomphalaria alexandrina is a

freshwater snail.

2- The shell is glossy, yellowish or dark

brown in colour.

3- The shell is a discoidal in shape and

sinistral.

Shell

IV- Class: Bivalvia

A- Subclass: Lamellibranchia

1-Order: Eulamellibranchia

Anodonta rubens

Shell

Interior of the shell

General characters

1-The shell is dark brown in

colour and is formed of 2 lateral

valves hinged together along the

dorsal edge.

2- The apex or umbo of the shell is small

and the concentric lines of growth

extending around the umbo and parallel

with the free edge.

3- The roughened areas on the smooth

surface which represent the insersions

of muscles include the anterior and

posterior adductors, the anterior and

posterior retractors and the

antero-ventral protractor.

Umbo

Lines of growth

umboHing ligament

anterior adductor

insertion

Protractor insertion

( The Freshwater Mussel)

Anterior retractor insertion

Posterior

retractor

insertion

Posterior

adductor

insertion

Palial line

Soft parts of Anodonta

General characters1- The mantle consists of 2 thin lobes.

2- The body muscles include the anterior and posterior

adductors, the anterior and posterior retractors and the

protractor muscles.

3- The foot is large ventrally located mass.

4- Two pairs of flattened labial palps are found below the protractor

muscles.

5- The gills are two large structures hang freely in the mantle

cavity, one on each side of the foot.

6- There are no eyes or tentacles.

Foot Protractor

muscle

Posterior adductor

muscle

Left mantle lobe

Right mantle lobegillLabial palp

Unio prasidens

Shell

T.S. of Unio

Interior of the shell

1- The shell is blackish brown in colour

and has a dark-brown periostracum.

2-The shell is equivalve and inequilateral, with a

variably oval shape.

3-The anterior margin of the shell is rounded and the

posterior elongated and truncated.

4-The umbo is prosogirated, rounded and prominent,

sometimes with tubercles.

5- The interior is white and shiny with well

marked pallial line between scars of both

anterior and posterior adductor

muscles.

General characters

General characters

1- The two mantle lobes are free ventrally

and fused dorsally

2- The foot protrudes in the middle and contains

parts of viscera especially intestine and gonads

3-The gill on each side is w-shaped with 2 v-shaped

halves of gill plates.

4- The heart lies mid-dorsally in the visceral

hump inside the pericardia cavity.

5- The two kidneys lie below the

pericardial cavity.

Mantle

lobe

Heart

Visceral

hump

Foot

Outer gill-plate

Inner gill-plate

Rectum

Gonad

Gut

T.S. Labial palps of Unio

T.S. of gill plate with ova

General characters

1-The gill-plate is composed of 2

lamellae formed of numerous filaments.

2-The two lamellae are connected by interlamellar

tissue junctions.

3- The gill-filaments are connected by interfilamentar

tissue junctions.

4- Each gill-filament is supported by a chitinous

rod and covered by a ciliated epithelium.

Ridges

Gill-filaments

Ova

Interlamellar

tissue

junctions

Interlamellar

spaces

General character

1- The opposite surfaces of each

two palps contain numerous ridges

and ciliated furrows the cilia of which

drive the food toards the mouth.

Ciliated furrows

Ostia

T.S. of gill plate without ova

Ostia Gill-filaments

Cardium edule

Shell

Pinctada radiata

Shell

Interior of the shell

General characters1- The two shell valves are connected

together and hinged dorsally through an

elastic ligament as well as a number of interlocking

teeth.

2- Each valve is marked externally with raised ribs

radiating out from the umbo.

3- The inner concavity of the valve is continued

dorsally beyond the hing line into the umbo.

General characters1- The shell is externally greyish green

or brown purple with white or yellowish radial

rows of projecting scales.

2-The umbo is subterminal and slightly projected

beyond the straight hinge.

4- Rough sculpture of concentric ridges are

usually more projecting at the margins and

hinge without teeth.

(The Pearl Oyster)

Circe corrugata

Shell

Donax trunculus

Shell

Interior of the shell

General characters

1- Circe corrugata with comarginal ribs covering

all the external surface.

2- Typically, this species does not have highly inflated valves,

and the ligament is external but slightly sunken beneath the

flank of the shell.

3- The pallial sinus is absent or very shallow.

General characters1- The shell is small and whitish in colour.

2- The umbo points backwords.

3- In the free ventral edge of each valve there is

a row of close-set of minute teeth.

Glochidium larva of Unio

Mytilus edulis

Shell

Hook

Larval byssus

Shell

General characters

1- It enclosed in 2 triangular.

delicate, hinged shell valves with

the edge drawn into a spiny hook.

2- The mantle lobes bear sensory

bristles.

3-The foot is rudimentary and bears

a long adhesive thread;

the larval byssus.

General characters

1- The Mytilus edulis is a

medium sized edible which is

found attached to rocks.

2-The shape of the shel is triangular

and with rounded edges.

3- The shell is smooth with fine

concenteric growth lines.

4- The shell is purple, blue or

sometimes brown in colour,

occasionally with radial

stripes.

Interior of the shell

2-Order: Filibranchia

Umbo

Lines of growth

Hinge

Lithophaga lithophaga

T.S. of gill plate

Whole

Piece of gill plate

actre

General characters

1- The shell valves are brown

in colour and have smooth surface.

2- The shell is long, more or less

cylindrical and with rounded endings.

3- Umbonal part is found near the

anterior end of valves.

4- The shell margins are smooth

and growth lines are fine.

Gill-filaments

Gill-filaments

General characters

1- The gill plate is composed

of 2 lamellae formed of

numerous gill-filaments.

2- The two lamellae are connected

by interlamellar tissue junctions.

3- The gill-filaments are joined

with another by ciliary

junctions.

Inter-filamentar

ciliary junctions

(date-mussel)

Tissue junction

V-Class: Cephalopoda

A- Subclass: Dibranchiata

1-Order: Decapoda

Sepia savignyi

Shell

ventral view

General characters

1- The body is divided into head and visceral

hump separeted by a short neck.

2- The head carries two large eyes and mouth surrounded by

a circular lip.

3- The visceral hump is somewhat elongated and has a pair of

fins extended along the two lateral sides.

4- The mouth is surrounded by 8 short and pointed arms and 2

elongated tentacles.

5- The inner surface of the arms and the ends of the tentacles

are covered by 4 rows of stalked,

cup-shaped suckers.

1- The shell is formed of calcium carbonate and protein.

2- It is concealed within the mantle and secreted by it and layers

being added throughout the animals life.

3- It serves for muscle attachment and for support.

General characters

tentacle

Visceral hump

Funnel

Arms

Suckers (The Cuttlefish)

Lateral fin

Eye

The shell of Sepia (cuttle bone)

2-Order: Octopoda

Octopus vulgaris

Lateral view

General characters

1- The body is divided into 2 regions; head and visceral hump.

2- The head is large and bears mouth and two large eyes.

3- The mouth is surrounded by 8 long arms each of which bears 2 rows of

sessile suckers and connected together by a web.

4- The visceral hump is soft, rounded posteriorly and has no fins or

shell.

Arms

Suckers Funnel

Eye Head

Visceral humpMantle

opening

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