Phylum Mollusca

Mollusc Characteristics 90,000+ living species 70,000+ fossil species Mantle Pair of dorsal folds of the body wall Forms a mantle cavity Modified into gills or lungs Secretes shell Coelom Limited to area around heart

Mollusc Characteristics (continued) Muscular Foot Variously adapted for locomotion Radula Odontophore - supporting cartilage of the radula

Mollusc Characteristics (continued) Open Circulatory System Trocophore larva Veliger sometimes follows trocophore

Class Polyplacophora Chitons ~ 1000 species 7 or 8 dorsal plates Numerous gills found in the mantle cavity

Chiton Anatomy

Class Scaphopoda Tusk Shells ~ 900 species Tubular tusk shaped shell Captacula - mucus-covered, ciliated tentacles

Scaphopod Anatomy

Class Gastropoda Snails, slugs, limpets, whelks, conchs, periwinkles, sea slugs, sea hares, and sea butterflies ~ 70,000 species Well developed head Large flat foot Torsion - during development some body parts rotate relative to the mouth and head Coiling - the shell is coiled and typically conispiral

Gastropod Anatomy

Gastropod Torsion

Evolution of Shell Coiling in Gastropods

Conispiral shells are either right-handed (dextral) or left-handed (sinistral)

Figure: 16_34b Title: Gastropod mollusks Caption: (b) Spanish shawl sea slugs prepare to mate.

Gastropod Eggs

Class Bivalvia Mussels, Clams, Scallops, Oysters, and Shipworms ~ 15,000 species Two-lobed mantle Two valves Hatchet shaped foot Head is greatly reduced Most are filter feeders

Bivalve Anatomy

Bivalve Gills

Bivalve Hinge Ligament and Adductors

Bivalve Development

Glochidium Larvae of Freshwater Clams

Figure: 16_35b Title: Bivalve mollusks Caption: (b) Mussels attach to rocks in dense aggregations exposed at low tide. White barnacles are attached to the mussel shells and surrounding rock.

Class Cephalopoda Nautiluses, Ammonoids (extinct), Squids, Cuttlefishes, and Octopuses ~ 700 species Well-developed head with a brain and complex eye Foot modified into funnel and arms/tentacles Shell reduced or absent Ink glands in all except Nautiloids Chromotophores present

Nautilus Anatomy

Squid Anatomy

Figure: 16_36b Title: Cephalopod mollusks Caption: (b) The squid moves by contracting its mantle to generate jet propulsion, which pushes the animal backward through the water.

Cephalopod Eyes

Figure: 16_36a Title: Cephalopod mollusks Caption: (a) An octopus can crawl rapidly by using its eight suckered tentacles. It can alter its color and skin texture to blend with its surroundings. In emergencies this mollusk can jet backward by vigorously contracting its mantle.