Phylum Mollusca

Characteristics

• Soft-bodied invertebrate covered with protective mantle that may or may not form a hard, calcium carbonate shell

• Second largest animal phylum

• Have a muscular foot for movement which is modified into tentacles for squid & octopus

• Complete, one-way digestive tract with a mouth & anus

Characteristics

• Cephalization - have a distinct head with sense organs & brain

• Have a scraping, mouth-like structure called the radula

• Go through free-swimming larval stage called trochophore

• Body organs called visceral mass lie below mantle

Characteristics

• Bilaterally symmetrical

• Most have separate sexes that cross-fertilize eggs

• Use jet propulsion to move by forcing water out siphon

• Includes 4 classes --- Polyplacophora (chitons), Gastropoda (snails, slugs, nudibranchs, conchs & abalone), Bivalvia (clams, oysters, & mussels), & Cephalopoda (squid, octopus, & nautilus)

Class Polyplacophora

• Have a shell divided into 8 over-lapping plates and live on rocks along seashore feeding on algae

• ex: Chiton

Chiton

Plates

Girdle

Class Gastropoda

• Head has a pair of retractable tentacles with eyes located at the ends

• Have a single shell or valve (snails) or none (slugs)

• ex: Moon Snail, Abalone, Cowry, Nudibranch (sea slug), Sea Hare

Moon Snail

Abalone

Cowry

Nudibranch (sea slug)

Sea Hare

f – Foot g – Siphon h – Tentacle i – Eye j – Mouth l - Mantle

a – Mantle b – Foot f/g– Tentacle

Class Bilvalvia

• Sessile Filter feeders

• Have two-part, hinged shell (2 valves)

• Have muscular foot that extends from shell for movement

• Scallops clap valves together to move

http://youtu.be/xsh41CG3Pc8

Class Bilvalvia

• Mantle secretes substance called "mother of pearl" to surround irritants like grains of sand

• Oldest, raised part of shell called umbo

• Powerful anterior & posterior adductor muscles open & close shell Lack a distinct head

Class Bilvalvia

• Have a siphon that circulate water over the gills to remove food & oxygen

• Have heart & circulatory system

• Separate sexes with external fertilization of eggs

• ex: clams, oysters, scallops, mussels

Clams

Oysters

Scallops

Mussels

c – Foot d – Shell f – Mantle g – Eye

Adductor

Class Cephalapoda

• Most intelligent mollusk

• Well developed head

• Active, free swimming predators

• Foot divided into tentacles with suckers

Class Cephalapoda

• Use their radula & beak to feed

Class Cephalapoda

• Circulatory system

• Lack an external shell

• Highly developed nervous system with vertebrate-like eyes

• Separate sexes with internal fertilization

Class Cephalapoda

• Chromatophores in the skin can help change color for camouflage

http://youtu.be/IAGxTsEmGek

Squid

• Largest invertebrate is the Giant Squid

(~40 feet with an eye ball the size of a beach ball)

Squid

• 8 arms and 2 long tentacles to catch prey

• Can squirt an inky substance into water to temporarily blind predators

Squid

• Have internal shell called pen

• Female lays eggs in jellylike material & protects them until hatching

Vampire Squid

Bobtail Squid

a – Mantle c – Fin d – Head e – Arm g – Tentacle h – Sucker i – Beak

Octopus

• Eight arms

• Crawls along bottom looking for prey

Octopus

• Blue Ringed Octopus – live in coral reefs in the Pacific and Indian Oceans from Japan to Australia; recognized as one of the world’s most venomous marine animals.

Octopus

• Dumbo Octopus – live at extreme depths (10,000-20,000 feet)

a – Mantle c – Fin d – Head e – Arm g – Tentacle h – Sucker i – Beak

Cuttlefish

• Eight arms and two tentacles

• masters of camoflauge

Chambered Nautilus

• Most primitive living cephalopod dating back 450 million years

• 38 outer tentacles and inner (male = 24 / female = 48-52)

Chambered Nautilus

• Has an exterior shell with 38 chambers

• Lives in the outer chamber of the shell

• Secretes gas into the other chambers to adjust buoyancy

a – Shell b – chamber c – Siphuncle d – Eye e – Tentacle