Unit 8 - Molluscs Part 2

Polyplacophora, Gastropoda, Bivalvia, Cephalopoda

Chiton plates are partially or completely covered by the mantle in some species, shell is composed of 8 dorsal plates.

Numerous gills all along the sides in an elongate mantle cavity called the pallial groove.

Most have a coiled/whorled shell, formed through a developmental process called torsion. Some have no shell or flat shells.

right, dextral, left, sinistral.

Limpets and abalone, Slugs and nudibranchs.

Many nudibranchs eat cnidarians and sequester the nematocysts for personal use.

Prosobranch, Opisthobranch, Pulmonate

Most of the marine snails, moon snails, conch, limpets, whelks, abalone.

Most of the terrestrial and freshwater snails, No gills, has a highly vascualar area of mantle that works as a lung.

A large modified radula tooth shaped like a harpoon, is used to inject venom into prey.

Clams, oysters, scallops, mussels, no head or radula, filter feeders

Umbo points anteriorly and is the oldest part of the shell, Foot is hatchet shaped and used for digging. Has 2 tubes called incurrent and excurrent siphons.

Nautilus, Squid, Cuttlefish, Octopus, all marine and predatory.

Dorsal part of foot forms several arms or tentacles. Ventral part of foot forms a siphon that drains the mantle cavity.

Mantle is muscular and used for propulsion by jetting water out the siphon.

Have very complex eyes like vertebraes, convergent evolution. Have rapid control of chromatophores in skin to change color and patterns.

Has beak-like, chitinous jaws for biting off pieces of food and delivering venom in some, Radula is present in most and used to chew.

Nautilus

By changing the amounts of fluid and gas in their shell chambers via a siphuncle.

Internal shell, Calcareous cuttle bone has many small chambers.

Closed circulatory system.