Phylum Mollusca

General Features

size range & diversity

vary and unique to all classes

mantle

feeding nad locomotion

feeding

locomotion

Aplacophora

less than 5cm

Polyplacophora

2-12 cm but big as 30cm

dorsoventrally flattened

Monoplacophora

3-4cm in diameter

dome-shaped

Cephalopoda

15mm-18mm

Bivalvia

1m; 1000kg

Gastropoda

1mm-50cm

spiraled

Scaphopoda

2-8cm

Tubular, tusk-shaped

Covers the visceral mass

extensions secrete mucus

secretes the shell

three layers

lacks in Aplacophora

periostracum

middle prismatic

inner nacreous layer

calcareous spines

reduced in cephalopods

multiple in polyplacophora

eight articulating plates

defense mechanism

surrounds the girdle

only present in polyplacophora

siphon - bivalves

cavity

house ctenidia

cilia on surface

lacks in gastropoda and scaphopoda

Feeding and Locomotion

feeding

locomotion

mouth in the anterior end

contains radula

biological file or scraper

absent in bivalves

captacula (sticky ends)

only present in scaphopoda

algae and organic matter

muscular foot

houses the visceral mass

contains dorsoventral and transverse muscles

works with hemocoel

forms the hydrostatic skeleton

forms funnel - cephalopods

absent in aplacophora

works with mucus

in form of retrograde waves

Forms and Functions

external features

internal features

head

foot

mantle

mantle cavity

contains tentacles

captacula in scaphopods

labial palps in bivalves

arms in cephalopods

body cavity

fluid-filled hemocoel

nervous system

tetraneural

pair of ganglia

pair of nerve cords

attached to the brain

pedal nerve cords

apical brain and suboesophageal ganglia fuse together

forms ring around esophagus

sensory structures

statocyst and osphradia

gastropoda

eyespots

image-forming eyes

cephalopods

aesthetes

polyplacophora

Digestive system

digestive glands

absent in carnivore's species of gastropods

crystalline style

intestine

anus

opens in the mantle cavity

Circulatory system

heart

three in cephalopods

absent in scaphopods

surrounded by pericardial cavity

open

except cephalopods

paired metanephridia

opens into pericardial cavity

Nephridiopores

opens into mantle cavity

Respiratory system

pigment = hemocyanin

Reproductive System

gastropoda

gas exchange through mantle

scaphopoda

gills equipped with cilia

bivalve

dioecious

monoecious

Monoplacophora

trochophore and veliger larva

gonads

unique in all classes

unpaired - scaphopoda

single - gastropoda

embedded in foot - cephalopoda

posterior end - cephalopoda

exteriorly - monoplacophora

on pericardial cavity - polyplacophora

spermatophore and hectocotylus arms in cephalopods

gonoducts in polyplacophora