What is a Mollusk? Soft body with internal or external shell Ex: snails, slugs, clams, squids, and octopi Trochophore larva
Body plan: Foot – takes on many forms Mantle – covers the body Shell – (present in most), made by glands in the mantle Visceral mass – internal organs
Feeding: Herbivores, Carnivores Filter feeders (clams, Oysters, scallops) Parasites Many feed using a flexible tongue shaped structure called a radula. (snails, slugs)
Respiration: Aquatic mollusks – snails, clams – breathe using gills in the mantel cavity Land snails breathe with a “lung” – a mantle cavity with a large surface area and many blood vessels.
Circulation – can be open or closed Open works better for slow moving mollusks (less efficient) Closed works better for fast moving mollusks (more efficient) Excretion – tube shaped nephridia Response – nervous systems vary from simple to complex Reproduction – many reproduce sexually with external fertilization, Tentacled mollusks this is usually internal A few are hermaphrodites All have a free swimming trochophore larva !
Groups of Mollusks Three major classes of mollusks 1. Gastropods 2. Bivalves 3. Cephalopods
Gastropod snails, slugs, and nudibranchs Shell-less or single shelled Move by a muscular foot Some are poisonous, bright colors
Nudibranchs (sea slugs) Check out the nudibranch gallery at nationalgeographicnudibranch gallery at nationalgeographic
Bivalves (things with 2 shells) Such as clams, scallops
Cephalopods octopi, squids, cuttlefish, and nautilus soft-bodied, head is attached to foot foot is divided into tentacles with sucking disks small internal shells or no shell at all
Cuttlefish (the chameleon of the sea)
Nautilus is only cephalopod with shell Squid have a modified shell called a pen Well developed eyes most complex of the mollusks