Coelomate Protostomes Phylum Mollusca Phylum Annelida Phylum Arthropoda 27 Sept.2014 Mollusks.ppt

Protostomes Three major phyla share three embryonic characters Spiral cleavage Mouth develops at site of blastopore (1st mouth) Mesoderm develops from lips of blastopore as solid masses, splits “split” coelom 27 Sept.2014 Mollusks.ppt

Protostomes Formation of Mesoderm and Coelom Solid masses of mesoderm separate from lips of blastopore. Split opens in mesoderm to form “split” coelom 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Phylum Mollusca (Greek “soft”) Body plan ~100,000 species, 2nd largest phylum Body plan Tube-in-tube, Protostomous Bilateral symmetry Coelomate, “split” coelom Marine, aquatic, terrestrial 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Body with three parts Visceral mass (“torso”) Mantle Mouth, gut, heart, gill, reproductive organs Mantle Sheet of tissue attached to middle of back Mantle cavity = space between mantle & visceral mass Foot Single muscular sheet contacts substrate Creeps with 100’s of little muscles 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Visceral mass (“torso”) Mantle Foot Mantle cavity = space between mantle & visceral mass Foot 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Unique, distinguishing characters Mantle Foot Radula Mantle cavity Foot Radula Tooth-bearing scraping “jaw” 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Ways the needs of cells are met Food Scrape algae etc. or filter-feeders Squids and Octopus are predators O2 and CO2 exchange Gills, or mantle cavity as “lung” Waste removal “kidney” with duct to mantle cavity 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Style in “stomach” Hard crystalline rod of digestive enzymes Spins in stomach, wraps string of mucus and food Ground away at posterior end along with mucus and food 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Special concerns of a multicellular animal Circulation: Open circulatory system Coordination: Brain & ventral nerve cords, Structural support: Hydrostatic &/or shell Movement: Muscles in foot Maintenance of water balance: “kidney” Reproduction Usually sexual, sexes usually separate, some hermaphrodites 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Coelom reduced to pericardial cavity Open Circulatory System No blood vessels (almost) Blood pumped forward through head, then oozes through visceral mass, around organs, muscles, gills, back to heart Hemocoel 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Nervous system Brain small, surrounds esophagus Pair of visceral nerve cords Pair of pedal nerve cords 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Class Polyplacophora Class Gastropoda Class Bivalvia chitons Class Gastropoda snails, slugs, nudibranchs Class Bivalvia clams, mussels, oysters, shipworm, etc. Class Cephalopoda squids, Octopus, cuttlefish, Nautilus 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Class Polyplacophora Chitons Thick mantle with eight shell plates Scrape algae, etc. from rocks 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Class Gastropoda snails, slugs, nudibranchs Torsion Bending & twisting of gut Conical, spiral shell 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Class Gastropoda 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Class Bivalvia clams, mussels, oysters, etc. Filter feeders Gill used as filter Radula usually lost Shells on left, right 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Class Cephalopoda Octopus, Squids, Nautilus, cuttlefish, Siphon on mantle edge “rocket” away from predators Tentacles with suction cups 27 Sept.2014 Mollusks.ppt

Phylum Mollusca Class Cephalopoda Octopus Complex behavior, learning 27 Sept.2014 Mollusks.ppt