30.3 - Molluscs PAges 620-622

Overview Phylum mollusca Protostome 1st embryonic opening becomes mouth Includes Annelids and Arthropods

Body structure Visceral mass – soft bodied, contains internal organs Foot – strong, muscular portion; used for locomotion Mantle - membranous/muscular covering enveloping visceral mass Mantle cavity is space between mantle folds May create shell

Also have head region with eyes and sense organs Classified by foot modification: Gastropods Cephalopods Bivalves

NudiBranchs, conchs, and snails Gastropods NudiBranchs, conchs, and snails

Foot is ventrally flattened Movement by muscle contractions along foot Nudibranchs ("sea slugs") lack shells Conchs and snails have coiled shells Where visceral mass follows Land snails have mantles with blood vessels, function as a lung

octopuses, squids, and nautiluses Cephalopods octopuses, squids, and nautiluses

Body structure Means "head-footed" No shell Foot evolved tentacles around head Beak and radula (toothy tongue)

Response to stimuli Cephalization Eyes have lens/retina with photoreceptors Brain formed by ganglia fusion with nerves connecting to parts of body

Movement Nerves control rapid contraction of mantle Allows quick movement by jet propulsion

Clams, oysters and scallops Bivalves Clams, oysters and scallops

Body structure Shells made of 2 parts Secreted by mantle (made of protein no calcium carbonate) Valves held together by adductor muscles

Feeding and digestion Organs include mouth, labial palps, esophagus, stomach, intestine, and kidneys Filter feeder Siphon draws particles into mantle cavity Siphon – posterior opening between 2 valves Mucous secretions collect particles around gills Ciliary action sweep towards mouth

Circulatory system Coelom is reduced Heart located below hump of shell (pericardial cavity) Pumps blood into dorsal aorta, then to organs In organs, blood flows through sinuses "Open circulatory system"

Nervous system Consists of 3 pairs of ganglia (anterior, foot, posterior) Connected by nerves Lack cephalisation

Excretory system 2 excretory kidneys beneath heart Remove waste from pericardial cavity into mantle cavity

Locomotion "hatchet" foot extends from anterior of shell Expands tip of foot, pulls body forward

Reproduction Sexes usually separate Gonads (ovary or testis) around intestine coils all Have a larval stage