Name: Molluscs; Mollusks.
Genera: 85000 species.
Habitat: marine, freshwater, and terrestrial.
Use: important food source; pearls, mother of pearl; Tyrian purple dye; sea silk; shells as money.
ZoologyMullusca are invertebrate animals; about 23% of all marine organisms; many live in freshwater and terrestrial habitats; highly diverse, in size, anatomical structure, behaviour, habitat.
The hypothetical, "generalized" mollusc has a single, limpet-like shell on top, which is made of proteins and chitin reinforced with calcium carbonate, and is secreted by a mantle that covers the whole upper surface.
Their nervous system consists of two paired nerve cords, or three in bivalves. The brain, in species that have one, encircles the esophagus. Most molluscs have eyes, and all have sensors that detect chemicals, vibrations and touch. The underside of the animal consists of a single muscular "foot".
Mollusca are coelomates, but the coelom is very small.
Mollusca have a mantle with a significant cavity used for breathing and excretion.
Their main body cavity is a hemocoel through which blood circulates in an open circulatory system.
Their have a radula, a rasping tongue. They have a complex digestive system in which exuded mucus and microscopic, muscle-powered "hairs" called cilia play various important roles.
Reproduction; eggs with external fertilization; trochophore larvae, more complex veliger larvae, or miniature adults.
Heart and nephridia ("kidneys") are important parts of the reproductive system as well as the circulatory and excretory systems.
CladesAplacophoraBivalvia: clams, oysters, mussels, scallops, and many shells
Cephalopoda: squid, cuttlefish and octopus; most neurologically advanced.
Polyplacophora: sea cradles.
Gastropoda: snails and slugs; 80% of the mollusca.
MonoplacophoraPleistomollusca
PolyplacophoraRostroconchia, extinct.
Scaphopoda.