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Echinoderms
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no distinct head
means “prickly skin”
!oral vs aboral surface
include: starfish, sea cucumbers, basket stars, brittle
stars, sea lilies, etc
outer surface of body is covered by epidermis
has an extremely abundant and diverse fossil record
below epidermis is an endoskeleton made of
hardened plates (=ossicles) of calcium
all marine; found in all oceans at all depths
movement & food gathering done predominantly by
water vascular system
some of the most abundant of all marine
invertebrates
a series of tubes that open to the sea through a
sieve plate (=madreprite)
almost all are bottom dwellers
mostly drab colors
filled with fluid (mainly sea water)
but a few are red, orange, purple, blue, etc
inside the body the tubes extend into each arm
of the 12 major animal groups (phyla) this one is
closest to the vertebrates (us)
connected to muscular tube feet
Unique Echinoderm Characteristics:
the tip of the tube feet are flattened, forming
suckers
1. most with 5-part radial symmetry
suctionlike cups can produce strong
force
2. unique water vascular system for feeding and
movement
the whole system operates hydraulically by
muscle contractions & opening and closing
valves
3. pedicellariae for protection
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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tube feet are used to cling to substrates, move and
to feed
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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in many echinoderms the body surface bears small
jaw-like pedicellariae
echinoderms are particle feeders, scavengers or
predators
! protect against animals and debris that settle
on the animals surface
no parasitic species
Reproduction & Development
most echinoderms have a very simple digestive tract
sexes typically separate ! dioecious
gas exchange and excretion occur through tiny
saclike projections that extend through epidermis
usually external fertilization: eggs and sperm are
released into the water
= dermal branchae
produce a free-swimming planktonic larva
the same functions are also shared by tube feet
in most groups
many also have excellent powers of regeneration
! can regenerate from 1/5th of oral disc & a single
arm
the nervous system consists of nerve fibers that
circle the mouth and nerves that branch off
into each arm to coordinate movement
but may require up to a year
some deliberately cast of an arm as a means of
asexual reproduction
echinoderms have no brain or centralized
processing area
don’t seem to age ! can liver forever?
tube feet are innervated by nervous sysem
some examples of echinoderms:
! enables all feet to move in single direction
eg. starfish ,seastars & sunstars
few specialized sense organs
bottom dwellers that inhabit all seas
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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margins of each groove are guarded by moveable
spines
common along littoral zone in coastal waters
where they may congregate in very large numbers
range from ~1/2”
(1 cm)
to 3’
(1 M)
tip of each arm has 1 or more short tactile and a
red eye spot
in diameter
on other side of central disc is a large sieve plate
eg. giant Pycnopodia has over 20 arms and is the size
of a manhole cover
often brightly colored: red, orange, blue, purple, green
etc
and numerous pedicellariae on central disc and
arms
keeps skin free of sponges, corals, etc
body composed of arms projecting from a
central disc
also used in feeding and defense
most with 5 arms
Feeding and Digestion
sunstar up to 40 arms
a. many starfish are scavengers
some have up to 50 arms
b. a few are suspension feeders
arms not sharply set off from central disc
feed on small plankton and organic debris
in some arms are very short or absent
mucous strands carry food to the mouth
eg. Culcita ! a pentagon with no arms
the mouth is in the center of bottom (oral) surface
c. most are carnivores
wide grooves (= ambulacral grooves)project
from mouth into each arm
feed on molluscs, crustaceans, polychaetes and
other echinoderms
each groove contains 2-4 rows of tube feet
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
use chemoreceoptors to detect and locate prey
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some can locate buried prey and dig down to
get them
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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starfish can regenerate from an arm
Sexual Reproduction
eg. some swallow prey whole and regurgitate
undigested ossicles & spines, etc
most are dioecious
eg. some attack larger seastars and begin eating the
end of an arm and work their way up
gonads in small area at base of each arm under
the digestive gland
eg. many are able to evert their stomachs through the
mouth to engulf and eat prey
when filled with eggs sor sperm they almost
completely fill arm
eg. some feed exclusively on bivalves
! some, such as asterias, are notorious predators of
oysters
egg and sperm are released through pores in
the skin
wraps itself around its prey
1 female may shed 2.5 M eggs
exert steady pull on valves
in about a half hour the adductor muscles of
bivalve fatigue and relax slightly to create a
small gap between the shells
sea stars are often the top predators in some benthic
communities
only need 0.1mm gap to insert stomach and
digest oyster
though unpalatable to most organisms to some they
are the preferred meal:
takes 2.5 - 8 hrs to digest a bivalve
eg. some fish with strong teeth
digestive glands in each arm receive the food from the
stomach to complete digestion and absorption
Reproduction & Development
eg. sea otters
eg. brittle stars basket stars
the most active members of the phylum
Asexual reproduction
found in all types of marine benthic habitats
many starfish regularly reproduce asexually
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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tend to be secretive
when fish takes an interest in the area under the starfish it
quickly wraps its arms around it
hide in cracks and crevices on hard substrates
eg. sea urchins, sand dollars & sea biscuits
some can burrow
all are benthic
have arms with central disc but:
remain close to the substrate
long thin arms sharply set off from disc
ossicles of arms are arranged into flexible
columns connected by muscle strands
compact body enclosed within a test (a single shell) of
ossicles or plates locked together into a single
unit
very few tube feet
most are more or less hemispherical in shape
all visceral organs are confined to central disc
no arms, but 5 rows of pores on test through
which very long tube feet extend
typically 5 arms
also with numerous long moveable spines
but in basket stars they repeatedly branch to
produce tentacle like mass
in most urchins, moveable spines cover most of
the body
movement by snake-like movements of arms
have ball & socket joints with tubercles on test
can rapidly clamor over rocks and seaweed
collagen fibers can make spines stiff and erect for
protection
brittle stars are carnivores, scavengers, deposit
feeders or filter feeders
in some urchins spines are hollow and can inject a
painful poison
some ”ambush” their prey
use arms to hold central disc off grand to form a kind of shelter
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Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
use very long tube feet and prehensile spines to move
around
most sea urchins are grazers
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body becomes elongated; long and wormlike
or “cucumber shaped”
with mouth and anus are on opposite ends
scrape algae from substrates with teeth
body has a leathery appearance
mouth contains a complex chewing mechanism of
5 converging teeth attached to muscle bands
ossicles are very small; the tougher skin provides
most of the support
used to scrape and chew algae from rocks
sea cucumbers crawl on bottom side of body
eg. Sea Cucumbers
relatively sluggish
rule the deep ocean benthos
lie on bottom or burrow into mud
! make up 90% of biomass on deep ocean floor
some live beneath stones or in coral crevices
often on sandy or muddy bottoms
there are a few deep water pelagic (swimming) forms
some crawl on sea floor
that have tube feet modified into fins, sails, or
medusa-like bells
others hide beneath rocks
some are burrowers
mouth is always surrounded by 10-30 tentacles
which are part of the water vascular system
sea cucumbers are among the strangest of the
echinoderms:
tentacles are highly retractile
like sea urchins have no arms
! can be completely retracted into mouth
tend toward bilateral symmetry:
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
tube feet can also be modified into sensory
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Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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papillae, fins, sails, etc
many sea cucumber are capable of evisceration
the front or back end ruptures and the internal organs are
expelled
sea cucumbers are mainly deposit feeders and
suspension feeders
seems to be a seasonal phenomenon
use tentacles to collect food and deliver it to
mouth
possibly when food is scarce or in order to eliminate wastes
stored inside the internaltissue
their digestive system is better developed than in
most echinoderms
the organs are later regenerated
may also be a protective mechanism
mouth opens into a muscular pharynx
a few sea cucumbers posess a large mass of white,
pink, or red tubules (= tubules of Cuvier)
attached to the base of their respiratory tree
then to esophagus and stomach
most have a long, looping intestine
when irritated or attacked, the anus is directed toward
the intruder and the tubules are shot out of the anus
leads to anus which opens into cloaca
in some the tubules are sticky; in others they release a toxin
cloaca = chamber in which digestive system, excretory
system & reproductive system all open into
small crabs and lobsters may be rendered completely
harmless and helpless
most have a respiratory tree consisting of two highly
branched tubes
the sea cucumber later regenerates the tubules for the
next attack
it’s also attached to the cloaca
pumping action of cloaca circulates water
a tropical pearlfish makes its home in the respiratory tree of
some sea cucumbers
leaves at night to search for food
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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Ecology & Human Impacts
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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don’t transmit any diseases
1. “crown of thorns” starfish destroys Pacific coral
reefs
although handling poisonous forms can be lethal
5. as food:
feed on coral polyps
eg. in China and Pacific Islands sea cucumbers are
boiled and dried and eaten as a delicacy
or used as a food flavoring
sometimes attack in “herds”
the number of reef attacks is increasing
in some areas collecting has severely depleated their
populations
sometimes results in extensive damage
eg. roe (gonads & eggs) are sold, raw or roasted,
as a delicacy in Japan and in sushi restaurants
very expensive to control outbreaks
2. sea urchins destroy kelp forest
>30M pounds of urchins were harvested in 1986
but are preyed on by sea otters
6. echinoderms have been widely used in
developmental research
3. predatory starfish can devastate commercial clam
or oyster beds
“we know more about the embryology of echinoderms
than probably any other embryo”
eg. a single starfish can eat a dozen clams or oysters in a day
sometimes an infestation is treated with quicklime
! destroys dermal branchiae and kills animal
! but also kills many other soft bodied invertebrates;
but not the oysters who temporarily close their
shells
4. echinoderms never attack humans
Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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Animals: 1409 Echinoderms; Ziser Lecture Notes 2009
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