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Echinoderms. Developed By Adam F Sprague & Dave Werner MATES Biology (Marine Bio Book – Ch.7) (Biology Book – Ch.40 also pp.682-686). 5 classes of Echinoderms. Sea star or starfish (Asteroidea) Brittle stars, basket stars, serpent stars ( Ophiuroidea )

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Developed By Adam F Sprague & Dave Werner

MATES Biology

(Marine Bio Book – Ch.7)

(Biology Book – Ch.40 also pp.682-686)

5 classes of echinoderms
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
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 echinoderms4
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
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
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 echinoderms8
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
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
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 asteroidea12
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 asteroidea13
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 ( and WH Freeman (, used with permission.

sea urchin echinoidea
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 echinoidea18
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 echinoidea20
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
Sea CucumbersHolothurians(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
sea cucumbers holothurians holothuroidea25
Sea CucumbersHolothurians(Holothuroidea)
  • Ecology and range of sea cucumbers
    • Rubble, rocks and sand. Also seen on some sponges in large aggregations.
sea cucumbers holothurians holothuroidea26
Sea CucumbersHolothurians(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 holothuroidea27
Sea CucumbersHolothurians(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
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 crinoidea32
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
brittle stars ophiuroidea
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 ophiuroidea35
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 ophiuroidea37
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

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."