Echinoderms
Developed By Dave Werner
BIOL265
(Marine Bio Book – Ch.7)
5 classes of Echinoderms
Sea star or starfish (Asteroidea)
 Brittle stars, basket stars, serpent
stars (Ophiuroidea)
Sea urchins, heart urchins and
sanddollars (Echinoidea)
Holothurians or sea cucumbers
(Holothuroidea)
 Feather stars and sea lilies
(Crinoidea).
Characteristics of Echinoderms
radial symmetry
body = 5 equal segments, each
containing duplicate set of internal organs
Pentamerous radial symmetry
no heart, brain, eyes, but some brittle
stars have light sensitive parts on arms
Mouth-situated on underside & anus on
top (except feather stars, sea cucumbers
& some urchins).
Characteristics of Echinoderms
tentacle-like
structures =tube feet
w/ suction pads
tube feet hydraulically
controlled by vascular
system- supplies
water through canals
Water creates suction
effect
Ecology and range of Echinoderms
exclusively marine
occur in various
habitats from
intertidal zone to
bottom of deep sea
trenches & from sand
to rubble to coral
reefs and in cold and
tropical seas.
Behavior of Echinoderms
Some carnivorous (i.e. sea star), detritus
foragers (i.e. sea cucumbers) or planktonic
feeders (i.e. basket stars)
Reproduction carried out by release of sperm &
eggs into water. Most species produce pelagic
(= free floating) planktonic larvae which feed
on plankton
Behavior of Echinoderms
 can regenerate missing limbs, arms, spines - even
intestines (i.e. sea cucumbers).
 Some brittle stars & sea stars can reproduce asexually
by breaking a ray or arm or by deliberately splitting the
body in half. Each half = whole new animal.
Sea stars (starfish)
(Asteroidea)
Characteristics
radial symmetry, several arms (5 or multiplied
by 5) radiating from a central body
 Mouth & anus close together
water intake (madreporite)
upper surface is often very colorful.
Minute pincer-like structures called pedicellaria
are present. These structures ensure that the
surface of the arms stay free from algae.
underside is often a lighter color
Sea stars (starfish)
(Asteroidea)
Ecology and range or sea stars
The starfish lives everywhere in the coral
reef and on sand or rocks
Sunflower Sea Star Locomotion - youtube
Sea stars (starfish)
(Asteroidea)
Behavior of sea stars
majority are carnivorous -feed
on sponges, bryozoans,
ascidians & molluscs
detritus feeders (detritus =
organically enriched film that
covers rocks) or scavengers.
Some are specialized feeders,
i.e. crown-of-thorns feeds on
live coral polyps.
Sea stars (starfish)
(Asteroidea)
Behavior of sea stars
regeneration
(asexual reproduction = autotomy):
In others the body is broken into unequal parts
(= fission) then the missing limbs regenerate
Anatomy of an adult sea star. Lower (right) image is a cross
section through an arm of the adult sea star. Images from
Purves et al., Life: The Science of Biology, 4th Edition, by
Sinauer Associates (www.sinauer.com) and WH Freeman
(www.whfreeman.com), used with permission.
Sea urchin
(Echinoidea)
Characteristics of sea urchins
Radial symmetrical body with external chitinous
skeleton and a centrally located jaw (called
Aristotle's lantern) with horny teeth
mouth consists of a complex arrangement of
muscles and plates surrounding circular opening
 The anus is located on the upper surface. Some
sea urchins have a spherical, bulb like cloaca (to
store fecal material) that protrudes from the anal
opening. can be withdrawn into shell.
Sea urchin
(Echinoidea)
– Ecology and range of sea urchins
Rubble and sand. An abundance of sea
urchins can be a sign for bad water
conditions
Army of Sea Urchins – BBC Video
Sea Cucumber expelling intestines
Sea urchin
(Echinoidea)
Behavior of sea urchins
Locomotion by tube feet & spines
generally nocturnal
Most are algal grazers -some feed on sponges,
bryozonans and ascidians and others on detritus
(detritus = organically enriched film that covers
rocks).
The sexes are separate & young are formed
indirectly by the fusion of sperm and eggs
released into the water.
Sea Cucumbers
Holothurians (Holothuroidea)
Characteristics of sea cucumbers
holothurians are radial symmetry
as name suggests, they are cucumber
shaped w/ an elongated, muscular, flexible
body w/ mouth at one end & anus at the
other. Tentacles around mouth (modified
tube feet) used in food collecting
Hairy Sea Cucumber
Sea Cucumbers
Holothurians (Holothuroidea)
Ecology and range of
sea cucumbers
Rubble, rocks and
sand. Also seen on
some sponges in large
aggregations.
Sea Cucumbers
Holothurians (Holothuroidea)
Behavior of sea cucumbers
Most species feed on rich organic film
coating sandy surfaces
crawl over bottom ingesting sand. The edible
particles (organic matter such as plankton,
foraminifera and bacteria) are extracted when
passing through their digestive tract &
processed sand is expelled from anus (as
worm-like excrements).
Sea Cucumbers
Holothurians (Holothuroidea)
Behavior of sea cucumbers
move by means of tube feet
When attacked they shed a sticky thread like
structure which is actually parts of their guts. The
so called Cuverian threads are toxic (the poison is
called holothurin) and can dissuade many
potential predators. These structures quickly
regenerate.
Feather stars
(Crinoidea)
Characteristics of feather stars
– Characteristics of feather stars
AKA- crinoids.
radial symmetry
The body is cup-shaped, their numerous feathery
arms project from a central disc
5-200 arms, called pinnules-coated w/sticky
substance to catch food.
appendages known as cirri attached to the
underside of the body with which they cling to to
sponges or corals.
mouth and their anus on upper side.
Feather stars
(Crinoidea)
 Ecology and range of
feather stars
primarily nocturnal but
seen in the open during
the day with arms rolled
up.
Crinoid stalks and blastoid
heads are common fossils
in certain parts of North
America.
Specimen of the
Carboniferous crinoid
Paradichocrinus planus
Feather stars
(Crinoidea)
– Behavior of feather stars
Feather stars can crawl, roll, walk and
even swim but usually they cling to
sponges or corals. Feather stars are very
abundant in areas exposed to periodic
strong currents, because they feed on
planktonic food.
Feather Star Feeding – youtube
Monterey Bay – Crinoids
Brittle stars
(Ophiuroidea)
Characteristics of brittle stars
– Characteristics of brittle stars
close relatives of sea stars
radial symmetry-five snakelike arms
no replication of internal organs, just one set
in the central disk
Compared to starfish, brittle stars have a
much smaller central disc and no anus
 Wastes are eliminated through the mouth
on underside
Brittle stars
(Ophiuroidea)
Ecology and range of brittle stars
very cryptic & hide in crevices under corals
 Best seen at night time, when they emerge
to feed on plankton. Usually at places
exposed to strong currents.
Brittle stars
(Ophiuroidea)
Behavior of brittle stars
Brittle arms= an escape mechanism.
arms regenerate quickly and an entire new
organism can regenerate, if the broken arm is
attached to a seizable portion of the disk
reproduce asexually by self-division
Brittle stars are the most active and fastest
moving echinoderms
Common Brittle Star
Why are the echinoderms the
most advanced of the
invertebrates?
The answer lies in the development of the embryo. If
you were to watch an embryonic starfish develop, you
would see that it begins life bilaterally, but switches
to radial symmetry as it matures.
 Deuterostome means "mouth second“
 In the earliest stages of embryo development, when there are only
a few cells and the embryo resembles a tiny globe of cells, a small
pucker develops on one side of the embryo. This grows into a
pocket, and allows some cells to migrate inside to form an
additional layer of cells within the outer layer.
 At this stage, the embryo is known as a gastrula. In the
Protostomia, which is the other major group of the Bilateria, the
mouth develops from the edge of this pocket, where the inner and
outer layer of cells meet; the anal opening develops later.
 In the Deuterostomia, the reverse is true; the pocket edge
develops into the anus, and the mouth is formed later. "Your mouth
comes second."
 http://www.ucmp.berkeley.edu/phyla/deuterostomia.html
http://www.pgjr.alpine.k12.ut.us/science/whitaker/Ani
mal_Kingdom/SeaStar/SeaStar.html
http://www.occ.cccd.edu/faculty/mperkins/zooreview/sea-star/