Today’s Objectives:

TSW list key characteristics of mollusks, including, but not limited to,– Major organs/organ systems– Major classes and representatives– Economic importance– Evolutionary history– Other major characteristics

Mollusks

New evolutionary steps

Protostomes, characters including– Trochophore larvae

– Spiral cleavage

– Schizocoelous coelom formationEucoelomateAdvanced brain (some classes)

Key characteristics

Head-foot Visceral mass Mantle & mantle cavity True coelom only in cavities around

– Heart – Nephridia– Gonads

True circulatory system Radula often present

Gastropoda – Gut Foots

Includes snails, limpets, & slugs Freshwater, marine, and terrestrial Display torsion Shell coiling Move on mucus with cilia or use foot

Gastropod Feeding Methods

Use radula to scrape algae Some radula modified to pierce prey Protostyle in digestive cavity

Gastropod Respiration & Circulation Gas exchange in mantle cavity Can have 1 or 2 gills Some have a siphon

Open circulatory system Blood acts as a hydraulic skeleton

Gastropod Nervous System

Nerves concentrated into large ganglia Most ganglia in head Simple or complex eyes Statocysts Chemoreceptors

Gastropod Excretory System

Nephridium (nephridia – plural) Ammonia is the primary waste product

in aquatic species Uric acid is the waste for terrestrial

species

Gastropod Reproduction

Can be monecious or dioecious Usually cross-fertilize inside the mantle

cavity First development of a penis Marine gastropods produce a veliger

larva

Economic Importance of Gastropods

Garden pestsGood eating – escargot

Major intermediate host for several nasty parasitic infections

Representative Gastropods

Nudibranchs – sea slugs Helix pomatia – escargot Garden slugs

Bivalvia – 2 Shells Umbo Hinge Nacre – mother of

pearl Shell made of

calcium carbonate

Bivalve Respiration & Circulation Gills expanded into multi-layered sheets

(lamellae) Usually 2 siphons – incurrent &

excurrent

Open circulatory system

Gastropod Feeding & Digestion

Labial palps filter food particles Mucus food string Crystalline style Gastric shield

Bivalve Nervous System

Ganglia located in esophagus, foot, and adductor muscle

Most sense organs located in margin of mantle (some have eyes there too)

Statocysts Chemoreceptors

Bivalve Reproduction

Most are dioecious, some monoecious Gonads in visceral mass Fertilization usually external

Bivalve Development

Trochophore larva Veliger larva Glochidium – often parasitic

Bivalve Economic Importance

Often used as food Pearl production Invasive species – zebra mussel

Representative Bivalves

Mytilus – common mussel Pinctada – pearl oysters Dreissena polymorpha – zebra mussel

Cephalopoda – Head Foots

Octopi, squid, nautili, cuttlefish Tentacles Jet Propulsion Closed Circulatory System

Cephalopoda Shell

External on nautili Internal in squid (pen) Internal in cuttlefish (cuttlebone) Absent in octopi

Cephalopoda Locomotion

Use siphon for jet propulsion Squeeze mantle cavity forcefully Sometimes have external “wings” or fins

for steering or slow locomotion Nautili use internal air for neutral

buoyancy

Cephalopoda Feeding

Most capture prey by sight– Use arms or tentacles to grab (sometimes

have hooks and suckers)– Bring prey to beaked mouth

Muscular digestive system Digestion in stomach and cecum Anus near the funnel

Cephalopoda Respiration & Circulatory Systems Closed ciculatory system – more

efficient 3 hearts High metabolic rates

Respiration through gills

Cephalopoda Nervous System Complex brains Very advanced, large eyes Statocysts Touch receptors Chemoreceptors Chromatophores – color changing,

signalling Some bioluminescent Ink gland

Cephalopoda Reproduction & Development

All are dioecious Males have testes and package sperm

in spermatophores Fertilization mostly internal in back of

female’s mantle cavity– Octopi have external fertilization of eggs

Often males have hectocotylus All larval development inside eggs.

Economic Importance of Cephalopods Research on nervous system Bait Food – calamari Minerals for pets – cuttlebone

Representative Cephalopods

Loligo – common squid Architeuthis dux – giant squid Octopus dofleini – Giant pacific octopus

The Vampire Squid from Hell!!!!

Polyplacophora – Many Plate Bearing Animals Used for food – hard to chew Chitons Crawl over floor using muscular foot Can roll into a ball for protection Most feed on algae Ladderlike nervous system

Chiton

Scaphopoda – Boat feet

Often called “tusk shells”

Burrowing animals

Conical shell open at both ends

Often feed on foraminiferans

Dioecious

Monoplacophora – One Plate Bearing Animals Dioecious Considered

living fossils Neopilina Live in deep

ocean

Caudofoveata – Animals with Tails in Small Pits Wormlike Deep sea floor dwellers Spicules on body wall

Aplacophora – No Plate Bearers

Also called solenogasters

Lack a shell Nervous system

similar to flatworms

Live on corals Carnivores