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BIOL 1030 – TOPIC 15 LECTURE NOTES
Topic 15: Deuterostomes: Echinodermata and Hemichordata (Ch. 33)
I.
Deuterostomia (clade)
A. defined primary by molecular evidence
B. some defining developmental traits (see previous notes), but those can get fuzzy
C. clade includes the following phyla that we will cover:
II.
1.
Phylum Echinodermata (clade)
2.
Phylum Hemichordata (clade)
3.
Phylum Chordata (clade)
Phylum Echinodermata - urchins, sea stars, sea cucumbers
A. marine; ~7000 living species; in fossil record back to over 650 MYA
B. name means “spiny skin”, reference to their endoskeleton
1.
calcium rich plates below skin
2.
living tissue when formed; usually fused into hard shell in adults
3.
pores in endoskeleton for water vascular system (madreporite, tube feet)
C. water-vascular system - hydraulic system for moving, feeding
1.
water enters though madreporite, opening typically opposite mouth
2.
water from madreporite moves though stone canal
3.
water then enters the ring canal that encircles the esophagus
4.
radial canals extend from ring canal into the 5 body parts, establishing basic symmetry
5.
radial canals branch out into tube feet
6.
contraction of muscular sac (ampulla) at base of tube foot causes fluid to be forced into tube foot, extending it – used for
movement
D. pentaradially symmetrical - derived trait, larvae are bilaterally symmetrical
E. coelom – relatively large; used for circulation and respiration
F.
asexual reproduction - many will regenerate if a broken part contains part of the central nerve ring, sometimes they will break
on purpose
G. sexual reproduction - form free-swimming larvae that are bilaterally symmetrical
H. six classes, all apparently monophyletic
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BIOL 1030 – TOPIC 15 LECTURE NOTES
I.
Class Crinoidea - sea lilies and feather stars
1.
mouth and anus on same side
2.
5-200+ arms, filter feeders
3.
primitive, sessile
4.
sea lilies – have calcareous stalk 15-30 cm long (20 m in some fossils)

“living fossils”

once much more common one of the dominant forms of life in the marine fossil record of the Paleozoic era (both in
numbers and size)
5.
J.
feather stars - no stalk
Class Asteroidea - sea stars or starfish
1.
1 cm - 1 m across
2.
to 10,000 m deep
3.
groove runs along each arm bordered by rows of tube feet
4.
tube feet are like little suction cups and create an impressive force
5.
feed mainly on bivalves

attach to either side of shell with tube feet

wait until bivalve fatigues

extrudes stomach into opening and digest prey
K. Class Ophiuroidea - brittle stars
1.
look like sea stars, but more flexible, move via serpentine motion of arms, groove closed below arms
2.
tube feet used to capture small prey and as sensory structures
L. Class Echinoidea - sea urchins and sand dollars
1.
no arms
2.
usually move via spines operated by tube feet
3.
vegetarians
M. Class Holothuroidea - sea cucumbers
1.
elongate
2.
often with leathery skin
3.
mouth surrounded by 8-30 modified tube feet called tentacles
4.
other normal tube feet move animal
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BIOL 1030 – TOPIC 15 LECTURE NOTES
5.
will extrude their foul-smelling stomachs when frightened
N. Class Concentricycloidea – sea daisies
III.
1.
recently discovered
2.
no arms
3.
tube feet on edge of disc, instead of along radial lines
Phylum Hemichordata (acorn worms)
A. ~90 living species; all marine
B. centimeter to meter size range; burrowing; proboscis, collar, and trunk
C. name means “half chordates”; transitional group to phylum Chordata
D. ciliated larvae resemble sea star larvae
E. form a clade with Echinodermata (group called Ambulacraria)
F.
share with chordates:
1.
dorsal nerve cord as well as ventral nerve cord
2.
part of dorsal nerve cord hollow in some
3.
throat with pharyngeal gill slits
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