Phylum Mollusca

● molluscus means “soft”● soft-bodied animals that have an internal or

external shell● include: snails, slugs, squid, octopi● share similar developmental stages

What is a Mollusk?

Has 4 parts:● foot- muscular (can be: flat, spade-shaped,

tentacles)● mantle- layer of tissue that covers most of the

body● shell- secreted by the mantle ; has been lost or

reduced in some mollusks● visceral mass- consists of internal organs

Body Plan

Varies● herbivores● carnivores● filter feeders● detrivores● parasites

Feeding

Snail & Slugs use a radula for feeding:● flexible tongue-like structure covered with hundreds of teeth● scrape algae; drill holes in shells

Octopi use sharp jaws to eat prey:● some produce poisons

Clams, oysters & scallops filter feed:● use a siphon to move water in and out of body

Feeding

● aquatic mollusks breathe using gills inside mantle cavity

● land snails/slugs respire with mantle cavity that has large surface area○ oxygen diffuses across the surface of the

mantle

Respiration

Can be an open or a closed circulatory system:● open circulatory system- blood is pumped through a

simple heart into cavities called sinuses○ works well for slow-moving mollusks (snails,

clams)● closed circulatory system- blood pumped through

heart and blood vessels○ works for fast-moving mollusks (squid, octopi)

Circulation

How does a closed circulatory system benefit a mollusk who moves quickly?

● cells release nitrogen-containing waste in blood in form of ammonia

● nephridia remove ammonia from blood and release from the body

Excretion

Varies:● Bivalves (clams, oysters) have simple nervous system

○ ganglia○ nerve cords○ sense organs○ eyespots

● Octopi have highly developed nervous system:○ can remember things○ can perform complex tasks

Response

http://www.youtube.com/watch?v=ocWF6d0nelY

http://www.youtube.com/watch?v=SCAIedFgdY0

Many different ways:● snails- secrete mucus & use their foot● octopi- jet propulsion

Movement

Varies:● sexual

○ external fertilization (bivalves)○ internal fertilization (octopi, squid, some

snails)○ hermaphrodites (do not fertilize themselves)

Reproduction

Gastropods (Gastropoda: stomach- foot)● without a shell or have a single shell● move by using a muscular foot● include

○ snails○ nudibranchs○ slugs

Groups of Mollusks

Bivalves (Bivalvia: 2 hinged-shells)● 2 shells held together by 2 muscles● stationary most of the time● Include:

○ clams○ oysters○ mussels

Cephalopods (Cephalopoda: head-foot)● soft-bodied● head attached to foot● foot divided into tentacles/arms● Include

○ octopi○ squid○ cuttlefish

http://www.youtube.com/watch?v=JYDkzqCfJzg

Write a response to the video: “Kings of Camouflage”● What did you find the most interesting about cuttlefish?● What surprised you?● What did you learn?

Write a paragraph (5-8 sentences)