Echinodermata—Stuff to know
• Water vascular system
• Mineralized skeletal anatomy (know “hard”
parts)
• Phylum Echinodermata
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Subphylum Crinozoa
Subphylum Blastozoa
Subphylum Asterozoa
Subphylum Echinozoa
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Echinodermata—Phylum overview
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Deuterostomes
Pentameral (five-fold) symmetry
Internal skeleton made of ossicles or plates
Each arm with ambulacral groove for collecting
food
Water vascular system (including tube feet)
Rough, spiny epidermis
Exclusively aquatic and marine
Late Proterozoic–Holocene
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Soft anatomy
• Digestive system is usually one-way, with
mouth, digestive glands, and anus
– Brittle stars and some starfish lack anus
• Food particles may be transported to mouth
along ambulacral groove
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Digestive system
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Soft anatomy
• Water vascular system provides structural
support and assists in feeding, respiration,
locomotion and sensory perception
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Circumoral ring
Stone canal
Hydropore (madreporite)
Radial canal
Tube feet
Ampullae
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Water vascular system
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Skeleton
• Skeleton is secreted by mesodermal layer and is
therefore internal
• Two main skeletal types
– Theca (= calyx, test or disk) is a boxlike or saclike
enclosure made up of sutured or imbricated plates
(ossicles)
• Ossicles are single high-Mg calcite crystals; highly porous
– Loose sclerites are formed within the mesoderm for
strength and support
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Skeleton
SEM view of highly
porous ossicle
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Skeleton (cont.)
• Appendages include:
– Spines for protection
– Arms and brachioles for gathering food
• Arms are radial extensions of body with
ambulacral grooves and tube feet (e.g., in crinoids)
• Brachioles are food gathering appendages mounted
on recumbent ambulacral areas (e.g., in blastoids)
– Stems and holdfasts for attachment
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Skeleton (cont.)
Echinoderm with
recumbent ambulacral
areas (no arms)—and
four-fold symmetry
brachioles
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Crinoid
structural units of
stem are columnals
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Classification
Phylum Echinodermata
Proterozoic–Holocene
Subphylum Crinozoa
Cambrian–Holocene
Subphylum Blastozoa
Cambrian–Permian
Subphylum Asterozoa
Ordovician–Holocene
Subphylum Echinozoa
Cambrian–Holocene
asteroids
(starfish)
echinoids
(sea urchins)
ophiuroids
(brittle stars)
holothurians
(sea cucumbers)
Subphylum Homalozoa
Cambrian–Devonian
(relatively unimportant)
[don’t worry about grey boxes]
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Other points of interest
• Echinoderms are deuterostomes
– Style of larval coelomic development that links
the phylum with hemichordates and chordates
• Capable of regenerating lost appendages
and even internal organs
– Disaggregated occicles may contain live cells
up to one year after becoming sedimentary
grains
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Ways of life
• Many Paleozoic forms were attached, epifaunal
suspension feeders
– Paleozoic seas characterized by high primary
productivity and relatively inefficient predators
– Suspension feeders characterized by compact theca
and well developed arms/brachioles
• Mesozoic/Cenozoic forms are mostly infaunal
detritus feeders and heavily armored carnivores
– Possibly in response to decrease in primary
productivity, increase in burrowing activity, and
increase in efficiency of predators (especially fish)
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Subphylum Crinozoa
• Globular, tightly sutured calyx
• Long arms, often with pinnules
• Mouth in center of upper surface; anus
lateral
• Mostly without hydropore
• Mostly attached suspension feeders
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Subphylum Blastozoa
• Globular, tightly sutured calyx
– Advanced forms with few plates arranged in well
developed pentameral symmetry
• Recumbent ambulacral areas with brachioles
(but no arms)
• Mouth in center of upper surface; anus lateral
• Mostly with hydropore and accessory
respiratory structures
• Mostly attached suspension feeders
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Subphylum Blastozoa
spiracles and
hydrospires are
respiratory structures
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Subphylum Asterozoa
• Star-shaped theca with five large arms (or
multiple of five)
• Well developed ambulacral grooves
• Mouth in center of lower surface; anus on
upper surface
• Madreporite present
• Mostly mobile benthic carnivores and
scavengers
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Subphylum Asterozoa
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Subphylum Echinozoa
• Theca variably shaped; tightly sutured, reduced
or with sclerites only
• Mostly without appendages (no arms, brachioles,
stems)
• Mostly with mouth and anus at opposite ends of
theca; hydropore or madreporite near mouth
• Mostly benthic detritus feeders (pellet
producers)
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Subphylum Echinozoa
edrioasteroids
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Subphylum Echinozoa
sand dollar
echinoid
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