The phylum Mollusca is the largest and most diverse group of marine invertebrate animals. They all have soft bodies, though many secrete a hard shell which protects and encloses the vulnerable body.
There are five main classes of mollusc:
- Chitons or "coat-of-mail shells" (Polyplacophora)
- Sea snails & sea slugs (Gastropoda)
- Tusk shells (Scaphopoda)
- Bivalve shells (Pelecypoda)
- Cuttlefishes. squids and octpuses (Cephalapoda)
octopus - the cleverest invertebrates of them all?
Not only do cephalopods have well developed nervous systems and relatively large brains. but octopuses are capable of learning in the same way as vertebrates do, and they have memories too.
mollusc facts
- The molluscan body is soft and is typically divided into a head (absent from bivalves), a muscular foot and a visceral mass containing the body organs.
- In most species the body is protected by a hard calcareous shell, secreted by the edge of the mantle. The shell is mostly composed of calcium carbonate.
- The mouthparts may include a 'radula' rather like a rasping tongue. Grazers, such as limpets, have a hard, rasping radula with many small teeth, while carnivores, including the whelks, have a narrow radula for boring through shells of prey.
- The majority of non-bivalve molluscs are active herbivores, scavengers and predators.
Bivalves, like mussels and razorshells, are filter-feeders - that is, they sift their food from surrounding seawater siphoned through their body.
