Phylum Mollusca

I. CharacteristicsA. Bilateral SymmetryB. Presence of a muscular footC. Mantle formed by Dorsal Body wallD. True CoelomE. Complex Digestive SystemF. Gas exchange through gills, lungs, mantle, or body

surfaceG. Simple Excretory systemH. Simple nervous system, with true eyes in SOME speciesI. Simpler forms monoecious, more complex forms

dioecious.J. Larval form in all molluscs known as a trochophore

Molluscan Body Plan (general)

II. Class Gastropoda “Stomach footed” Molluscs

examples: Snails, Slugs, Whelks, Conchs, CowriesA. This is the largest and most successful class of MolluscsB. Shell, if present, is singular, and whorled around a common axis known as a columella.C. Right handed shells are dextral; left handed are

sinistral.D. Rasp like Radula used to scrape food.E. Eyes usually positioned on stalks on head.F. Most forms monoeciousG. Torsion occurs as larvae become adults, causing the

organs to lie above the head in the mantle cavity.

A. Dextral shell

C. Sinistral shell

Cross section showing columella

Queen Conch

Pulmonate Land Snail

BananaSlug

MarineCalliostoma

Gastropods – Univalves (1 shell)

Examples - snails, abalone

How to shuck an abalone:http://www.youtube.com/watch?feature=player_detailpage&v=WbEmnfY-niU

Gastropod videos – questions

How is water directed into the mantle cavity?What is the easiest way to tell a slug from a

snail?What is the primary organ of defense for

snails?Nudibranchs are marine gastropods that do

not have a shell. Are these considered snails or slugs?

Gastropods – Secrets of the Sea (pt.1)

http://www.youtube.com/watch?v=z6Z2XCdmEwU

III. Class BivalviaFormerly known as Class Pelecypoda

The “hatchet-footed” molluscs Examples: Clams, Oysters, Scallops, Mussels, cockles,

coquinasA.These organisms all have two shells.B.Bivalves are all sedentary filter feeders.C.Incurrent siphons bring water in, excurrent

siphons take water out.D.Bivalves secrete their shells using nacre, derived

from the compounds in the water.

Bivalves have two siphons for the exchange of nutrients and oxygen into their shells and bodies.

Examples of incurrent and excurrent siphons

Scallop

Giant Clams

Oyster

The Process of Pearl formation:

A . First, a grain of sand or other foreign material gets caught between the shell of the oyster, and the mantle, which is very tender and delicate.

B. Second, the irritant is surrounded by nacre, or mother-of-pearl, to ease the discomfort created by the sharp edges.

C. The oyster continues to secrete nacre until the pearl is formed in a large enough diameter to stop the irritation.

D. Naturally formed pearls are very rare to find, hence their value.

E. Kokichi Mikimoto, the son of a Japanese noodle-maker, was the first to force oysters to form rounded pearls, a process known as culturing. Today, Mikimoto pearls are the most widely sold cultured pearls in the world.

Tahitian Black Pearls

Golden South Sea Pearls from Indonesia $65,000

$12,000

Akoya Japanese Pearls

$24,000

IV. Class Cephalopoda“Head-footed Molluscs”

examples: octopus, squid, cuttlefish, nautilusA. The MOST ADVANCED of all mollusc classes

B. They feed on fishes, other molluscs, crustaceans and wormsC. They have a closed circulatory system – very advancedD. Use funnels for rapid locomotion backwardsE. Octopi are loners and have 8 arms (total = 8)F. Squid are gregarious and have 8 arms and 2 tentacles

(total = 10).G. Both secrete an ink-like substance known as sepia to

confuse their attackers.H. The largest Octopi reach a length of about 3 meters, the

largest squid (Architeuthis) reaches a length of about 60 feet.

I. Water movement in the mantle cavity serves three functions: oxygenation, locomotion, and waste and gamete removal.

Cephalopod vocabulary What cells allow a cephalopod to change color?

Chromatophores The only part of a shell that still exists in squid

Pen (supports the mantle)

Cephalopodshttp://www.youtube.com/watch?feature=player_detailpage&v=Q-jBksy7z8U

Beak -

Camouflaged -

http://www.youtube.com/watch?feature=player_detailpage&v=0GVaa9r1YFohttp://www.youtube.com/watch?v=IznlT8XkmkY&feature=player_embedded#!

Cuttlefish – master of camo 20 minutes later…….

Giant Octopus

Cuttlefish

Chambered Nautilus

Squid

Interesting Facts!

Phylum Mollusca is the second largest phylum, behind only the Phylum

Arthropoda

Most molluscs are found in the ocean

Molluscs are important economically for food and for pearls

The biggest predator of scallops is sea stars!