Phylum Mollusca Attributes of the molluscs Segmental Trochophore

Phylum Mollusca

Attributes of the molluscs • • Segmental Trochophore larvae Head, foot and body component Shell is secreted by mantle – Periostracum – Prismatic – Mother of pearl==nacreous • Radula in the mouth cavity • Have pairs of feather like gills--ctenidial gills • Paired excretory organs

Classes • • • Monoplacophora Polyplacophora Gastropoda Bivalvia Cepahalopoda Scaphopoda

Monoplacophora • • Neopilina-Missing links= Architype==theoretical construct Homeobox genes

Polyplacophora • • • Chitons Chitin--a complex mucopolysaacharide Pieces of eight=shell is in eight pieces Foot looks segmental Paired gills in the mantle cavity

Gastropoda • All mollusk characteristics • Shell – Simple – Coiled shell – Lacking • Torsion – Veliger – Walter Garstang

Cephalopoda • Head is surround by the foot in the form of arm/tentacles • Radula is present but vestigial, chitin jaws • Muscular mantle and siphon allows for jet propulsion • Paired ctenidial gills • Have a partially closed circulatory system with visceral and gill hearts • Very efficient digestive system

Kinds of cephalopods • Nautiloids • Chamber Nautilus – The Chambered Nautilus Poem • Squid (calamari) shell reduced replaced by chitinous pen • Cuttlefish • octopus

Bivalvia (Pelcypoda) • Shell of two halves • Mantle is often produced into a siphon – Incurrent/excurrent • Gill is sheet-like (lamellibranch) • Foot may be extensible or small or lacking – Gooeyduck, mussel, scallop • Most are filter feeders – Osphraedia in incurrent siphon detect the nature of the incoming stream

Scaphopoda • Shell elongate, hollow tube • Foot works similar to that of bivalves only circular in nature, with tentacle-like structures around • Lacks gills • Mantle cavity tubular • Wampum