Soft-bodied Animals More than 112,000 species Phylum Mollusca Soft-bodied Animals More than 112,000 species

General Characteristics Bilateral Symmetry Reduced segmentation Three body parts Head (contains mouth)muscular foot: Locomotion, digging, supports internal organs May be modified in squid and octopus Visceral Hump (above the head) Contains the internal organs (heart, organs of digestion, reproduction and excretion) Mantle Thin body covering (contains calcium carbonate) Secretes shell Reduce surface area for gas exchange  evolved gills

General Characteristics Respiration Gills(protected in mantle cavity), lungs, mantle or body surface Nitrogenous wastes are excreted through nephridia Open circulatory system with dorsal heart and vessels, hemocoel for return of circulatory fluid Complete digestive system with mouth, radula= flexible tongue like strip of tissue covered with tough abarsive teeth that point backward Radula is used to graze, drill, or function as a poisonous dart (or beak i.e. octopus)

General Characteristics Nervous system with dorsal brain, nerve ring, pair of solid ventral nerve cords Reproduction: Sexual with the development of the trochophore larvae (nearly identical to annelids) Trochophore larvae becomes the veliger larvae swimming Has a shell Trochophore Larvae Veliger Larvae

General Characteristics True coelomates: Reduced main body cavity – the hemocoel Protostomes Mouth develops first in the embryo

Four classes Amphineura (polyplacophora) Bivalvia Gastropoda Cephalopoda

Class Amphineura (Polyplacophora) – the chitons Marine organisms Shell is made up of 8 articulating plates Have a muscular foot for locomotion (crawling) Reduced head

Chitons cont’d About 650 species of these organisms Cling to rocks in the intertidal zone and use a tooth-like radula to scrape food off of rocks (herbivores) Breathe through gills Gumboot Chiton

Class Gastropoda (Stomach-foot) Largest molluscan class Snails and Slugs, Sea slugs Characterized by a single shell with characteristic cone shape Breathe through gills (ctenidia) or the mantle cavity acts as a primitive lung (gas diffusion) Muscular foot extends along the ventral surface of the organism

Class Gastropoda Gastropods undergo a process called torsion during larval development The visceral mass twists 180 degrees in relation to the head Results in the mantle cavity, gills and anus being brought to the front of the animal Because of torsion the gastropod is able to retract its head into its mantle cavity when threatened

Gastropods cont’d Head contains a pair of antennae and a pair of eyes Scraping radula to pick up food Slug does not have a shell Usually becomes active during the cool moist part of the day Only molluscan class to become terrestrial Open circulatory system Circulatory fluid = hemolymph Herbivorous or carnivorous

Nudibranchs (Sea Slugs) Marine gastropods that lack shells Nudibranch means “naked gill” refers to the fact that gas exchange happens across the entire surface of these animals

Class Bivalvia (2 shells connected by hinge) Clam, Oysters, Mussels, Scallops (most are sessile) Mainly marine – living in intertidal zone Large visceral hump and a muscular foot with a reduced head covered with a thin mantle The mantle produces a cavity where the gills and 2 siphons (incurrent and excurrent) are found http://www.youtube.com/watch?v=ZBfviWg7kKM&feature=related Giant Clam

Bivalvia cont’d Filter feeders: Take water containing food into the mantle cavity and pass it over the mouth Excess water is forced out through the excurrent siphon Oldest part of the shell is the area surrounding the hinge (called the umbo) Exclusively marine No radula Swimming Scallop

Separate sex – external fertilization Burrow in sand or rock or attach to substrate by secreting byssal threads Many leap with a foot Separate sex – external fertilization Geoduck

Mmmm oysters!

Class Cephalopoda (Head-foot) Squids, octopuses, cuttlefish, and nautilus All members of this class are marine Squid and octopus are among the most intelligent of the invertebrates All carnivorous Have tentacles and a central mouth containing a sharp beak

Cephalopods cont’d Many of these organisms contain a large ink sac that is used when trying to escape from potential predators They have well developed eyes and brains They contain special pigment cells called chromatophores which enable them to change color Squid Candles

Cephalopods cont’d They have gills in the mantle cavity Their circulatory system is a closed one Jet propulsion: Can force water out siphon Catch prey with arms injecting poison with radula Internal fertilization – lay eggs

Squid External Anatomy http://www. youtube. com/watch

Squid Internal Anatomy