Mollusc Characteristics Unsegmented soft body –Visceral mass Molluscs have a Modified Foot –Muscular foot and/or tentacles Have a mantle (fold in the body wall that lines the shell) Most have shell (internal or external) –Or remnants of a shell Pen in squid

Tentacles/ modified foot head Mantle cavity Shell footMantle

Classes of Molluscs There are 8 classes of molluscs but this course will look at the 3 main classes. Class Cephalopoda – Octopus, squid and nautilus Class Gastropoda – slugs and snails Class Bivalvia – clams, mussels, scallops

Class Gastropoda free-living; marine, terrestrial, fresh water noticeable head single shell, often spiral muscular foot is attached near the stomach area

Pallial Lung In the Pulmonata subclass, the species hallmark is a functional lung, which the term, "pulmonate" refers to. The mantle cavity walls have become heavily vascularized and more or less form a lung sac ("pallial lung"). By expansion and contraction of the mantle muscles, this lung sac permits breathing air across a small opening to the outside. Thus, oxygen and carbon dioxide gases can exchange with the vascular system, and none of the pulmonate snails have (or needs) the gill.

Class Cephalopoda Exclusively marine Shell- “pen”- internal remnant of a shell Use fins and siphon to move Modified foot= tentacles Fast swimming predators -use tentacles to catch prey Have a special camera like eye Ex- Giant Squid

Squid External Anatomy Siphon Fins Mantle

Cephalopods are the only molluscs with a closed circulatory system. They have three hearts total: –two gill hearts (also known as branchial hearts) that move blood through the capillaries of the gills. –A single systemic heart then pumps the oxygenated blood through the rest of the body. Like most molluscs, cephalopods use hemocyanin, a copper-containing protein, rather than hemoglobin to transport oxygen. – As a result, their blood is colorless when deoxygenated and turns blue when exposed to air.[13][13]

Squid Internal Anatomy

Class Bivalvia marine and freshwater gill used for gas exchange all are sessile, suspension feeders and filter food from the water all have two part shells (bivalves)

Other Bivalves Limatula strangei. Some bivalves, such as the scallops are able to actively move when endangered by vigorously flapping their shells and squirting out jets of water. Limatula also moves very vigorously when disturbed. The tentacles around the mantle edge are sticky, very mobile and parts can break off them when the animal is disturbed, leaving a potential predator with a sticky writhing worm-like object to deal with as the Limatula escapes (25mm). The bivalves are the second largest class of molluscs. They differ from snails in having two shells, usually mirror images of each other. Some like oysters and mussels live attached to rocks and other hard surfaces while others, like pipis, burrow in sand. Leptonoidean bivalves (in picture) are a group which usually live commensally with other animals. Most have a large foot and are active crawlers (1mm).