MOLLUSCA

Instructor: Almonther I. Alhamedi

The Islamic University of GazaDepartment of Biology

E-mail : . .mhamedi@iugaza edu psWeb page: http:// . . . /site iugaza edu ps mhamedi

CHARACTERISTICS OF PHYLUM MOLLUSCA 1. Body bilaterally symmetrical (bilateral asymmetry

in some); unsegmented; often with definite head 2. Ventral body wall specialized as a muscular foot,

variously modified but used chiefly for locomotion 3. Dorsal body wall forms pair of folds called the

mantle, which encloses the mantle cavity, is modified into gills or lungs, and secretes the shell (shell absent in some)

4. Surface epithelium usually ciliated and bearing mucous glands and sensory nerve endings

5. Coelom limited mainly to area around heart, and perhaps lumen of gonads and part of kidneys

6. Complex digestive system; rasping organ (radula) usually present; anus usually emptying into mantle cavity

CHARACTERISTICS OF PHYLUM MOLLUSCA 7. Open circulatory system (mostly closed in

cephalopods) of heart (usually three chambered), blood vessels, and sinuses; respiratory pigments in blood

8. Gaseous exchange by gills, lungs, mantle, or body surface

9. One or two kidneys (metanephridia) opening into the pericardial cavity and usually emptying into the mantle cavity

10. Nervous system of paired cerebral, pleural, pedal, and visceral ganglia, with nerve cords and sub epidermal plexus; ganglia centralized in nerve ring in gastropods and cephalopods

11. Sensory organs of touch, smell, taste, equilibrium, and vision (in some); eyes highly developed in cephalopods

CLASS MONOPLACOPHORA

Neopilina, class Monoplacophora. Living specimens range from 3 mm to about 3 cm in length. A, Ventral view. B, Dorsal view.

CLASS POLYPLACOPHORA

Anatomy of a chiton

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CLASS SCAPHOPODA

Tooth shells Shell opens on both

ends Burrow into mud No gills

Mantle for gas exchange

Feed on detritus and protozoa

CLASS SCAPHOPODA

CLASS GASTROPODA

CLASS BIVALVIA

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CLASS CEPHALOPODA

Shell in squid and octopus absent or vestigial

Jet propulsion Ink sac Arms and tentacles Marine All predators

CLASS CEPHALOPODA

CLASS CEPHALOPODA