Echinoderms Developed By Dave Werner BIOL265 (Marine Bio Book – Ch.7)

5 classes of Echinoderms zSea star or starfish (Asteroidea)Sea star or starfish (Asteroidea) z Brittle stars, basket stars, serpent stars (Ophiuroidea)Brittle stars, basket stars, serpent stars (Ophiuroidea) zSea urchins, heart urchins and sanddollars (Echinoidea)Sea urchins, heart urchins and sanddollars (Echinoidea) zHolothurians or sea cucumbers (Holothuroidea)Holothurians or sea cucumbers (Holothuroidea) z Feather stars and sea lilies (Crinoidea).Feather stars and sea lilies (Crinoidea)

Characteristics of Echinoderms zradial symmetry zbody = 5 equal segments, each containing duplicate set of internal organs zPentamerous radial symmetry zno heart, brain, eyes, but some brittle stars have light sensitive parts on arms zMouth-situated on underside & anus on top (except feather stars, sea cucumbers & some urchins).

Characteristics of Echinoderms ztentacle-like structures =tube feet w/ suction pads ztube feet - hydraulically controlled by vascular system- supplies water through canals zWater creates suction effect

Ecology and range of Echinoderms zexclusively marine zoccur 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 zSome carnivorous (i.e. sea star), detritus foragers (i.e. sea cucumbers) or planktonic feeders (i.e. basket stars) zReproduction carried out by release of sperm & eggs into water. Most species produce pelagic (= free floating) planktonic larvae which feed on plankton

Behavior of Echinoderms z can regenerate missing limbs, arms, spines - even intestines (i.e. sea cucumbers). z 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 zradial symmetry, several arms (5 or multiplied by 5) radiating from a central body z Mouth & anus close together zwater intake (madreporite) zupper surface is often very colorful. zMinute pincer-like structures called pedicellaria are present. These structures ensure that the surface of the arms stay free from algae. zunderside is often a lighter color

Sea stars (starfish) (Asteroidea) zEcology and range or sea stars yThe starfish lives everywhere in the coral reef and on sand or rocks ySunflower Sea Star Locomotion - youtubeSunflower Sea Star Locomotion

Sea stars (starfish) (Asteroidea) zBehavior of sea stars ymajority are carnivorous -feed on sponges, bryozoans, ascidians & molluscs ydetritus feeders (detritus = organically enriched film that covers rocks) or scavengers. ySome are specialized feeders, i.e. crown-of-thorns feeds on live coral polyps.

Sea stars (starfish) (Asteroidea) zBehavior of sea stars xregeneration x(asexual reproduction = autotomy): xIn 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) zCharacteristics of sea urchins xRadial symmetrical body with external chitinous skeleton and a centrally located jaw (called Aristotle's lantern) with horny teeth xmouth consists of a complex arrangement of muscles and plates surrounding circular opening x 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 zRubble and sand. An abundance of sea urchins can be a sign for bad water conditions zArmy of Sea Urchins – BBC VideoArmy of Sea Urchins – BBC Video zSea Cucumber expelling intestinesSea Cucumber expelling intestines

Sea urchin (Echinoidea) zBehavior of sea urchins xLocomotion by tube feet & spines xgenerally nocturnal xMost are algal grazers -some feed on sponges, bryozonans and ascidians and others on detritus (detritus = organically enriched film that covers rocks). xThe sexes are separate & young are formed indirectly by the fusion of sperm and eggs released into the water.

Sea Cucumbers Holothurians (Holothuroidea) zCharacteristics of sea cucumbers yholothurians are radial symmetry yas 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) zEcology and range of sea cucumbers yRubble, rocks and sand. Also seen on some sponges in large aggregations.

Sea Cucumbers Holothurians (Holothuroidea) zBehavior of sea cucumbers yMost species feed on rich organic film coating sandy surfaces ycrawl 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) zBehavior of sea cucumbers xmove by means of tube feet xWhen 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) zCharacteristics of feather stars –Characteristics of feather stars xAKA- crinoids. xradial symmetry xThe body is cup-shaped, their numerous feathery arms project from a central disc x5-200 arms, called pinnules-coated w/sticky substance to catch food. xappendages known as cirri attached to the underside of the body with which they cling to to sponges or corals. xmouth and their anus on upper side.

zEcology and range of feather stars yprimarily nocturnal but seen in the open during the day with arms rolled up. yCrinoid stalks and blastoid heads are common fossils in certain parts of North America. ySpecimen of the Carboniferous crinoid Paradichocrinus planus Feather stars (Crinoidea)

–Behavior of feather stars zFeather 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. zFeather Star Feeding – youtubeFeather Star Feeding – youtube zMonterey Bay – CrinoidsMonterey Bay – Crinoids

Brittle stars (Ophiuroidea) zCharacteristics of brittle stars –Characteristics of brittle stars yclose relatives of sea stars yradial symmetry-five snakelike arms yno replication of internal organs, just one set in the central disk yCompared to starfish, brittle stars have a much smaller central disc and no anus y Wastes are eliminated through the mouth on underside

Brittle stars (Ophiuroidea) zEcology and range of brittle stars yvery cryptic & hide in crevices under corals y Best seen at night time, when they emerge to feed on plankton. Usually at places exposed to strong currents.

Brittle stars (Ophiuroidea) zBehavior of brittle stars yBrittle arms= an escape mechanism. yarms regenerate quickly and an entire new organism can regenerate, if the broken arm is attached to a seizable portion of the disk yreproduce asexually by self-division yBrittle 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. zDeuterostome means "mouth second“ zIn 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. zAt 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. zIn the Deuterostomia, the reverse is true; the pocket edge develops into the anus, and the mouth is formed later. "Your mouth comes second." zhttp://

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