Phylum Mollusca Chapter 12

Phylum Mollusca “soft” Three Main Classes Class Gastropoda (snails, slugs, limpets) Class Bivalvia (muscles, clams, oysters) Class Cephalopoda (octopus, squid, nautilus, cuttlefish) Limpets

Body Form Bilateral Symmetry Invertebrate - no backbone Hydrostatic Skeleton (fluid under pressure) Triploblastic Coelomate 1st animals to posses a coelom Yes, even before annelids… Small cavity; surrounds heart, nephridia, gonads Protostomate Blastopore become mouth – ‘primitive’

Functions of the Coelom Provides room for organ development Surface diffusion of Gases Nutrients Wastes Storage Elimination of reproductive products Hydrostatic support

Characteristics of Molluscs Size: <1cm – 18m Garden slug – Giant squid 3 Body Regions Mantle – tissue that covers the body May secret a shell Fxn: excretion, gas exchange, elimination of wastes, reproductive products Visceral mass – contains organs Head foot – elongate foot w/ anterior head

Characteristics of Molluscs (cont.) Open circulatory system in all except cephalopods Radula – rasping/scraping structure Covers tonguelike structure

Class Gastropoda Snails, limpets, slugs Over 35,000 species <Largest class> Habitat: Marine, freshwater, terrestrial Operculum ‘lid’ Dorsal posterior end Used for protection from predators & desiccation 6th Hr Left off Here 3/7/14

Class Gastropoda Undergo Torsion during larval stage- 180° Twist of visceral mass & mantle Allows head to enter shell first for protection Allows for clean water in front of the snail to enter mantle cavity Makes snail more sensitive to stimuli coming from the direction in which it moves

Class Gastropoda Locomotion Flattened foot Cilia over mucous trail Sometimes ciliated Muscular contractions Cilia over mucous trail

Class Gastropoda Nervous Communication Ospharidia Chemoreceptors Detect sediment & chemicals in inhalant H20 Helps detect prey Ganglia linked by nerves Eyes @ base or end of tentacles Photo receptors Lens & Cornea Statocysts in the foot (balance) 5th Hr. Left off Here 3/7/14

Class Gastropoda Cardiovascular: Respiration Open Circulatory System Blood “hemolymph” leaves blood vessels Blood bathes tissue directly in hemocoel ‘sinus’ Function of blood: transport nutrients, wastes, & gasses Respiration Gills Diffusion of O2 across mantle

Class Gastropoda Digestion Food trapped in mucus strings Gets incorporated into protostyle Protostyle – rotating ‘mucoid mass’ in gut of gastropod Radula Ciliated digestive tract 2nd Hour Left off Here

Class Gastropoda Excretory Waste Removal Wastes excreted through coelom from blood Aquatic – produce ammonia Terrestrial – produce uric acid (less toxic) – conserves water Nepheridium – excretory organ

Class Gastropoda Reproduction Marine snails – external fertilization Dioecious Gametes discharged into sea Freshwater & Terrestrial snails – internal fertilization Monecious Copulation - Exchange sperm – or - One snail may act as the male, the other as the female

Class Bivalvia “two-leaf” Mussels, clams, oysters, scallops Habitat: Marine, freshwater Help remove bacteria from polluted water 2 convex halves- valves Proteinaceous hinge

Class Bivalvia Tongue & grooves in shell to prevent twisting Umbo – swollen area – looks like a notch Oldest part of shell Sheet like mantle

Class Bivalvia Muscular movement: Adductor muscles to close shell Defense against predation Sea stars can break this muscle Steaming bivalves… Sessile (immobile)

Class Bivalvia Nervous Communication 3 pairs of interconnected ganglia Margin of the mantle is main sense organ has sensory cells Tentacles Photo receptors or Lens & Cornea Statocysts – balance/gravity Osphraidium – chemoreceptors in mantle

Class Bivalvia Cardiovascular System Respiration Open circulatory system Blood flow: heart  tissue sinuses  nepheridia  gills  heart Respiration Gills covered in cillia diffusion

Class Bivalvia Digestive System Filter feeders Gills trap food particles Move down food grooves (ciliated tracts) Labial palps sort food particles

Class Bivalvia Excretory System 2 Nepheridia Duct system Nephridiopores in anterior region for excretion of wastes

Class Bivalvia Reproduction Most dioecious – male/female Few monoecous – hermaphroditic Most external fertilization Spew out gametes and fertilize in sea Some internal fertilization (fresh water only) Female sucks in sperm from inhalent water Young clams shed from gills

Class Cephalopoda

Class Cephalopoda “head foot” Most complex mollusc All except nautilus have a reduced shell Cuttlefish & squid have internal shell Nautilus has a coiled shell for support Modified foot for food capture, attachment, locomotion, & reproduction Visceral mass located in head segment

Class Cephalopoda Muscular movement Jet propulsion Foot modified into tentacles

Class Cephalopoda Nervous Communication Highly developed nervous system Brains are large Fusion of ganglia Statocysts (gravity) Eyes

Class Cephalopoda Cardiovascular 1st to have Closed circulatory system Heart consists of 2 auricles and 1 ventricle Have contractile arteries and branchial hearts Respiration Gills & diffusion

Class Cephalopoda Digestive System Jaws & Radula Tentacles w/ adhesive cups or foot to capture prey Feed on small invertebrates Efficient predators