coelom.mollusk

INVERTEBRATE DIVERSITY SECTION (Biol.201), Spr 2000

Dr. Kathy S. Williams (email kwilliams@sunstroke.sdsu.edu)

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Coelomate Protostomes

Recall that previous Bilateria did not have true coelom. (591, 593) * FIG. 32.5

Protostomes & deuterostomes have a true coelom. (593-594)
    *FIG. 32.5 Animal clade
    *FIG. 32.1 Body plans of bilateria
    * FIG. 32.6 Development of protostomes and deuterostomes

What is a true coelom?

What features do all protostomes share?

See me (Dr. K. Williams) for information on how to fill this out, if you were not
in class or want more clarification.

There are 3 major protostome lineages. (591; *FIG. 32.3)

Mollusca
Annelida
the group of phyla called "arthropods"

(including Chelicerata, Crustacea & Uniramia)

Calcified protection: Molluscan diversity

VARIATIONS ON A THEME modifications of a great body plan allows many different activities

Modern mollusks (Mollusca) exhibit great complexity in form & function. (609-612)

*FIG. 33.16

novel body plan - protostome with calcified shells
novel feeding mode - using radula
movement by way of muscular foot
several other novel or modified internal features (see clade in lab manual)

    MOLLUSK EVOLUTION - Note how body plans with very similar body structures (gut systems,
            foot, gills, etc.) have variations that allow animals to live in different habitats and do
            different things. Examine similarities among the types, and also note differences.

CLICK ON FIGURE TO GET LARGER VIEW

Four variations on the molluscan body plan

Chitons (Polyplacophora) - built for sessile, aquatic life

Bivalvia (clams, oysters, scallops, mussels; * FIG. 33.32)

sedentary lifestyle w/ gills for respiration and feeding
hinged shells covering entire body
gills modified for feeding; loss of radula

Gastropods (Gastropoda; including snails, limpets, abalones, and nudibranchs) typically have spiral shells & move slowly using a large muscular foot. * FIG. 33.18

undergo embryonic torsion
achieved great diversity - on land & in the sea•
invasion of land required modified respiratory structures
• open circulatory system can mean slow movement

Cephalopod mollusks (Cephalopoda; including nautiluses, squids, and octopuses) are built to be fast predators.

locomotion; "jet propulsion" via siphon
well-developed sense organs
large gills and a "beak-like" jaw
tentacles derived from molluscan foot
closed circulatory system

* genus Nautilus = "living fossils"

BY NOW YOU SHOULD BE ABLE TO:

Describe a true coelom
Explain features shared by all protostomes
Explain characteristics that distinguish phylum Mollusca from the other animal phyla.
Describe the basic body plan of a mollusk and explain how it has been modified in the
Polyplacophora, Gastropoda, Bivalvia, and Cephalopoda.
Distinguish among the following 4 molluscan taxa & give examples of each: a) Polyplacophora,
b) Gastropoda, c) Bivalvia, and d) Cephalopoda.