Phylum: Mollusca (continued)

•Gastropods:–Meaning “stomach-footed” - a head with a flattened foot

–May or may not have a shell

I. Shelled Gastropods (Snails)

• A. Digestion: One way digestive tract (in the mouth, out the anus)

• B. Circulation: Have a 1 chambered heart

• C. Breathing: Breathes by taking water into its siphon tube, which brings it to internal gills

D. Movement in snails:

• Moves along surfaces by a muscular foot

• Have 2 sets of tentacles: Anterior (front) and Posterior (back):–Front pair are used for a sense of touch

–Back pair are used for seeing

Types of Snails

1. Mud Snails:•Are scavengers – eat dead or dying organisms

•Use a Radula to tear and shred dead matter

Mud snails on a dime

2. Moon SnailsFeed on live clams• Secrete a chemical out of

the foot to soften the shell • Uses a radula to drill a hole

in the shell• The snail inserts its mouth

and eats the clam

3. Cone Snails

• Are predatory snails• Have toxins which are used to

kill prey–These toxins are of great interest to scientists and are being studied for their benefits to humans

Anatomy of a cone snail

Cone snail’s harpoon-like radula

•Used to spear small fish

•Then delivers poison to its prey

II. Shell-less Gastropods1.The Sea Hare

A. Appearance: Have no shells or the shell is very small

B. Diet: Graze on algaeC. Protection: Some

release dark ink for protectionD. Life cycle: (beginning

to end) is about 1 year

E. Reproduction: Are Hermaphrodites – Male at the front end and female at the back end

Sea Hare reproduction

Are HermaphroditesAre Male at the front end and female at the back end

They can be seen mating in large chains

They lay up to 80 million eggs in a group, and resemble spaghetti

California Brown Sea Hare

• The largest gastropod in the ocean

• Can grow up to 2½ feet long

2. Nudibranchs or Sea Slugs

Name means “Naked Gills” (gills are easily seen on its back)

Are more than 3,000 species worldwide

Have Rhinophores (-tentacles on top of the head used for finding food and a mate)

Rhinphores of a nudibranch:

Nudibranchs (continued)

•Many have finger-like structures on their back called cerata

•Many are brightly colored, but a few have subtle colors for camaflouge

Cerata of a Komodo Dragon nudibranch:

Dorid Nudibranch

Dorid Nudibranch

Glossodoris Atromarginata

Blue Nudibranch