Phylum Mollusca!!Created by: Mariah Ghant, Saori Ishizuka, and Monica Lin

Germ Layers• 3 germ layers• Ectoderm• Mesoderm• Endoderm

Symmetry• Bilateral

Coelom• Mollusca are true coelom• Fluid filled cavity within the mesoderm

Digestive Tract• Extracellular digestion • Complete digestive tract• Mouth• Anus

Cephalization• Evident in mollusca• Cephalopods have eyes with image formation

• Neurons concentrate in a ganglial pattern

Segmentation• No segmentation• Instead, body divided into head, foot and visceral

mass

Skeleton & Appendages• Mollusca have soft bodies • Often protected by a shell• Some have lost their shells because of evolution

• Muscular tube feet • Skeleton• Shell with three layers: periostracum, prismatic layer,

nacreous layer

Circulatory System• Open circulatory system• Except for Cephalopods, blood does not circulate within

the vessels• Collected from the gills• pumped through the heart• released directly into spaces in the tissues from which

it returns to the gills and then to the heart• Closed circulatory system for cephalopods

Respiratory System• Gills in aquatic forms• Discrete respiratory system • Improved capacity for oxygen uptake and distribution• Increases body mass

Reproduction• Single or double set of gonads and ducts in each

sex• Bivalves and some snails of mollusca are

hermaphrodites

Habitat• Occur in almost every habitat found on Earth• Most are found in marine environments, extending

from the intertidal to the deepest oceans