lab/lecture 8: molusca general

Question 1

What is the basic body plan of mollusks?

Answer 1

Foot, mantle, shell; coelomate protostomes with reduced coelom, hemocoel, head-foot-visceral mass, complete gut, radula (except bivalves), mantle cavity with gills (ctenidia).

Question 2

Describe (phylum) mollusca fossils.

Answer 2

Soft-bodied organisms, but many have mineralized shells with excellent fossil records (best among invertebrates); shells show diverse shapes and ornamentation.

Question 3

Describe (class) Polyplacophora fossils.

Answer 3

Flattened body with 8 dorsal plates; plates often preserved, sometimes disarticulated; marine grazers on hard surfaces. (also called chitons)

Question 4

Describe (class) Gastropoda fossils.

Answer 4

Coiled or uncoiled shells; early forms show torsion (180° twist of body); shells with spires, apertures, and ornamentation; includes limpets, whelks, cone shells.

Question 5

Describe (class) Bivalvia fossils.

Answer 5

Paired shells (valves), usually symmetrical; strong growth lines; preserved as molds/casts; hinge features help ID; distinguish from brachiopods by plane of symmetry (between valves vs. across valves).

Question 6

Describe (class) Scaphopoda fossils.

Answer 6

Tubular, slightly curved shells open at both ends; resemble miniature elephant tusks; marine sediment dwellers.

Question 7

Describe (class) Cephalopoda fossils.

Answer 7

Chambered shells with sutures (ammonites, nautiloids); some with internal skeletons (squid, cuttlefish); complex eyes; beaks rarely preserved.

Question 8

Describe (class) Monoplacophora fossils.

Answer 8

Cap-shaped shells; once known only from fossils, rediscovered alive; simple, segmented body plan.

Question 9

Describe (class) Aplacophora fossils.

Answer 9

Rarely preserved; worm-like body with spicules instead of shell.

Question 10

Describe (genus) Lytoceras fossils.

Answer 10

Jurassic ammonite with coiled shell, complex suture patterns; important index fossil.