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
- Pedicellariae are present in some (primarily seastars and sea urchins)
- Calcareous endoskeleton composed of individual plates (ossicles)
- Marine environments; most are benthic
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Bipinnaria larva of a sea star
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Brachiolaria larva of a sea star
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Pedicellaria from a sea star (stained slide)
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Class Crinoidea — Sea Lilies & Feather Stars
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
See additional fossil crinoids here
Models of extinct crinoids, from left to right: Elegantocrinus (Carboniferous Period), Petalocrinus (Silurian), Ancyrocrinus (Devonian), Ammonicrinus (Devonian), and Scyphocrinites, a floating crinoid with the calyx pointing down (Silurian-Devonian)
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Feather Star, possibly Comantheria sp.?
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Sea Lily, Endoxocrinus prionodes, preserved specimen
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Japanese Sea Lily, Metacrinus rotundus, dried specimen
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Feather Star, dried specimen
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Fossil of Dichocrinus multiplex crinoid; Mississipian Period, IA
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Fossil of Culicocrinus thomasi (left) & Rhodocrinites douglassi (right); Mississipian Period, IA
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Fossil of Saccocoma pectinata, a floating crinoid; Jurassic Period, Germany
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Fossil of Ectinocrinus sp. Sea Lily calyx; Ordovician Period, KY
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Fossil of Scyphocrinites sp. calyx a floating species in which the calyx hangs down (see model); Silurian Period, Morocco
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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 (2 views).
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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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Mouth and oral surface of a Chocolate Chip Seastar, Protoreaster nodosus
See also labeled photo.
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African Red Knob Sea Star, Protoreaster linckii, Kenya
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Giant Spined Star, Pisaster gigantea; San Diego, CA
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Spiny Sand Star, Astropecten armatus
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Bat Star, Patiria miniata, 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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Pacific Blood Star, Henricia leviuscula
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Leather Star, Dermasterias imbricata; CA.
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Class Ophiuroidea — Brittle & Basket Stars
Characteristics
- Five arms articulated; distinct from body disk
- Arms may be branched (basket stars) or unbranched (brittle stars)
- Arms lack open ambulacral groove
- Lack anus
- Most are deposit or suspension feeders
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Western Spiny Brittlestar, Ophiothrix spiculata; CA
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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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Dried Brittlestar, possibly Ophiarachnella sp.; ventral view
See also labeled photo.
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Banded-arm Brittlestar, probably Ophioderma appressum?
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Basket Star, Gorgonocephalus sp.
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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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Closeup of mouth of live reef urchin, Echinometra viridis
See also labeled photo.
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Closeup of mouth of live variegated sea urchin, Lytechinus variegatus
See also labeled photo.
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Dissected Sea Urchin, Strongylocentrotus sp.
See also labeled photo.
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Aristotle's Lantern, the feeding apparatus of derived echinoids, Echinometra viridis
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Giant Keyhole Sand Dollar, Encope grandis; aboral and oral view of test.
See also labeled photo.
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Sand Dollar fossil, Dendraster gibbsii; Pliocene Epoch, CA.
See also labeled photo.
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Test of a Pink Sea Urchin,
See also labeled photo.
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Crown-spined Urchin, Plococidaris verticillata, dried test, oral side up
Eccentric Sand Dollar, Dendraster excentricus
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Heart Urchin, Maretia planulata, dried
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Shingle Urchin, Colobocentrotus atratus; HI
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Slate Pencil Urchin, Eucidaris tribuloides
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California Purple Urchins, Strongylocentrotus purpuratus; CA
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Reef Urchin, Echinometra viridis
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Black Long-spined Urchin, Diadema setosum
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Fragile Pink Urchins, Allocentrotus fragilis
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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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Dissected Sea Cucumber, Cucumaria frondosa
See also labeled photo.
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Burrowing Sea Cucumber, Leptosynapta albicans, San Diego, CA
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Warty Sea Cucumber, Parastichopus parvimensis, showing "ventral" tube feet and tentacles.
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Speckled Sea Cucumber, Actinopyga mauritiana; HI
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Yellow Sea Cucumber, Colochirus robustus, a suspension feeder
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Armored Sea Cucumber, Psolus chitonoides, a sedentary suspension feeder
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Extinct Echinoderm Classes
In addition to the 5 extant classes, there are also many extinct groups of Echinoderms
- Some were stalked suspension feeders, similar to crinoids
- Primitive forms were bilaterally symmetric or asymmetric
- You do not have to know these classes
See additional fossils of extinct echinoderm classes here
Models of extinct classes of echinoderms, from left to right: Caryocrinites (Class Cystoidea), Isorophus (Class Edrioasteroidea), Enoploura (Class Stylophora), Cothurnocystis (Class Stylophora), and Pleurocystites (Class Cystoidea). All date to the Ordovician Period.
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Fossil Eocrinoid, Gogia palmeri; Cambrian Period, ID (Class Eocrinoidea)
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Fossil Eocrinoid, Ascocystites sp.; Ordovician Period, Morocco (Class Eocrinoidea)
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Fossil Carpoid, Dendrocystites sp.; Ordovician Period, Morocco (Class Homoiostelea)
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Fossil Ctenocystoid, Ctenocystis utahensi; Cambrian Period, UT (Class Ctenocystoidea)
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Fossil Edrioasteroid, Isorophus cincinnatiensis, on a brachiopod shell; Ordovician Period, OH (Class Edrioasteroidea)
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Fossil Edrioasteroid, Spinadiscus lefebvrei; Ordovician Period, Morocco (Class Edrioasteroidea)
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Fossil Cystoid, Holocystites sp.; Silurian Period, IN (Class Cystoidea); the mouth is at the left.
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Stylophoran Fossil, Mitrocystites mitra; Ordovician Period, Chechia (Class Stylophora). The "tail" at the bottom is probably homologous to the stalk in crinoids, but was used to pull the animal across or through the substrate.
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Fossil Blastoids, Cryptoblastus melo; Mississippian Period, IL (Class Blastoidea). In life, the mouth is toward the right on both.
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