Echinoderm Characteristics
- Most species exhibit pentaradial symmetry as adults
- Larvae are bilaterally symmetric
- Unique water vascular system: internal fluid-filled canals
- Tube feet form external extensions of water vascular system
- Calcareous endoskeleton composed of individual plates (ossicles)
- Marine environments; most are benthic
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Class Crinoidea — Sea Lilies
Characteristics
- Body (=calyx) is cup-shaped with oral surface upwards
- Arms have numerous tiny branches (pinnules)
- Anus opens on oral surface
- Supported by aboral stalk (sea lilies) or tentacle-like cirri (feather stars)
- Suspension feeder in deep-sea environments
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Feather Star, dried specimen
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Fossil of Sea Lily calyx; Ordovician Period, KY
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Class Asteroidea — Sea Stars
Characteristics
- Body star-shaped with 5 or more arms
- Arms relatively thick; not distinct from central body disk
- Tube feet lie in open ambulacral grooves
- Gonads and digestive tract extend into arms
- Madreporite (opening to water vascular system) and anus aboral
- Mostly slow-moving predators
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Dissected Sea Star, Asterias sp.
See also labeled photo.
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African Red Knob Sea Star, Protoreaster linckii, Kenya
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Bat Star, Patiria miniata, CA
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Ochre Sea Star, Pisaster ochraceus, eating mussel (Mytilus sp.) (turned oral surface up; note ambulacral grooves and tube feet); CA
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Sunflower Star, Pycnopodia helianthoides; a top predator that feeds on other sea stars; CA.
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Linkia Seastar, Linckia sp.; the large arm was shed by the parent; the four shorter arms regenerated from this arm; Kenya.
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Leather Star, Dermasterias imbricata; CA.
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Class Ophiuroidea — Brittle Stars
Characteristics
- Five arms articulated; distinct from body disk
- Arms may be branched (basket stars) or unbranched
- Arms lack open ambulacral groove
- Lack anus
- Most are deposit or suspension feeders
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Little Brittlestar, Amphipholis pugetana; note regenerating arms; CA
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Banded Brittlestar, Ophionereis annulata; CA
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Basket Star, Gorgonocephalus sp.
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Class Echinoidea — Sea Urchins
Characteristics
- Body globular or disk-shaped; lack arms
- Skeletal plates fused into rigid test
- Pores in test allow tube feet to exit
- Spines moveable
- Protrusible jaw apparatus (Aristotle's Lantern)
- Mostly herbivores or detritivores, but some predatory
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Dissected Sea Urchin, Strongylocentrotus sp.
See also labeled photo.
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Giant Keyhole Sand Dollar, Encope grandis; aboral and oral view of test.
See also labeled photo.
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Shingle Urchin, Colobocentrotus atratus; HI
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California Purple Urchins, Strongylocentrotus purpuratus; CA
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Pencil Urchin, Eucidaris sp.
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Black Long-spined Urchin, Diadema setosum
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Class Holothuroidea — Sea Cucumbers
Characteristics
- Body elongated in oral-aboral axis
- Secondarily bilaterally symmetric (no dorsal tube feet)
- Skeleton reduced to isolated ossicles; soft-bodied
- Ring of tentacles around mouth
- Most are deposit feeders in soft sediments
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Speckled Sea Cucumber, Actinopyga mauritiana; HI
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California Sea Cucumber, Parastichopus californicus, showing "ventral" tube feet and mouth.
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Armored Sea Cucumber, Psolus chitonoides, a sedentary suspension feeder
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