INVERTEBRATE DIVERSITY SECTION (Biol.201), Spr 2000

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

Return to Invertebrate Introduction              Go to next topic                                    Return to Syllabus

ANNOTHER COLOMATE ROUTE --

DEUTEROSTOMES: ECHINODERMATA

Contrast protostome & deuterostome characteristics. (591, 593-594, 624)
(What’s a deuterostome?)  *FIG. 32.5, 32.1, 32.6

u embryonic cleavage
u development of coelom
u formation of mouth
Echinoderms (Echinodermata) are the most basal of the deuterostomes.
        (624-626; * FIG. 33.36, 33.37, clade)

Adults are radially symmetrical, although larvae are bilaterally symmetrical.

u complex body plan allows some species to have moderately active, slow-moving, lifestyle

u calcified internal skeleton (1012)

u water vascular system (624, * FIG. 33.37)

  Echinoderm diversity reflects many variations on the body basic plan.
        * FIG. on echinoderm body plans
                                        click on figure for larger view
u Crinoids (Crinoidea) are an ancient lineage & have up to several hundred arms.   Other modern echinoderms have oral surface down & fall into 2 groups:
u those that usually have many fewer arms (often only 5) • Sea stars (Asteroidea) - most familiar echinoderms; madreporite is aboral.

• Brittle stars (Ophiuroidea) - lost suckers on tube feet; madreporite is oral.
 

 u those that lack arms • Sea urchins (Echinoidea) have skeletal plates fused into globe- or disk- shaped test; grooves go from oral to aboral surfaces; have movable spines.

• Sea cucumbers (Holothuroidea) have fleshy sausage-shaped bodies; endoskeleton reduced; madreporite reduced; tube feet near mouth modified to serve as tentacles.

Quiz #6

You’re walking along a beach on a tropical island and come across a bunch of echinoderms in a tide pool …  You find an unusual animal among them and want to determine what it is.  You decide that is marine, has jointed appendages, and you see its bilaterally symmetrical larvae swimming around. You dissect one and find that it has a true coelom and complex excretory organs.

(2 pts)  Is this an echinoderm?  YES / NO (pick one)

(4 pts)  Briefly explain your answer (give only one feature that is critical - or diagnostic).