Higher Invertebrates Echinoderms Chapter 9 Higher Invertebrates Echinoderms

Echinoderms: Animals with Spiny Skins Phylum Echinodermata Include sea stars, sea urchins and sea cucumbers Larval forms exhibit bilateral symmetry but most adults exhibit a modified form of radial symmetry Mostly benthic, and found at nearly all depths Sea cucumbers and brittle stars are commonly found in deep-sea samples

Echinoderm Structure Endoskeleton: internal skeleton that lies just beneath the epidermis ossicles: plates of calcium carbonate

Echinoderm Structure Water vascular system: unique hydraulic system that functions in locomotion, feeding, gas exchange and excretion passes through a system of canals attached to some canals are tube feet

Echinoderm Sea Stars Class Asteroidea – sea stars Typically composed of a central disk + 5 arms or rays On underside, ambulacral grooves with tube feet radiate from the mouth along each ray Aboral surface: the side opposite the mouth, which is frequently rough or spiny

Figure 9-42 SEA STARS.

Sea Stars Feeding in sea stars most are carnivores or scavengers of invertebrates and sometimes fish prey are located by sensing of substances they release into the water sea stars envelope and open bivalves, evert a portion of the stomach, and insert it into the bivalves to digest them

Figure 9-43 SEA STAR FEEDING.

Echinoderm Ophiuroids Class Ophiuroidea e.g. brittle, basket and serpent stars Benthic with 5 slender, distinct arms, frequently covered with many spines Lack pedicellariae and have closed abulacral grooves Tube feet lack suckers and are used in locomotion and feeding Brittle stars shed arms if disturbed

Figure 9-44 (b) BRITTLE STARS.

Echinoderm Crinoids Class Crinoidea–sea lilies and feather stars Primitive, flower-like echinoderms Most are feather stars, which seldom move and cling to the bottom with grasping cirri Suspension feeders Can regenerate lost arms

Figure 9-49 (a) CRINOIDS.

Figure 9-49 (b) CRINOIDS.

Echinoderm Sea Urchins Class Echinoidea Body enclosed by test—a hard exoskeleton Benthic on solid surfaces (sea urchins) or in sand (heart urchins, sand dollars) Regular (radial) echinoids: sea urchins; spheroid body with long, moveable spines Irregular (bilateral) echinoids: heart urchins and sand dollars; have short spines on their tests

Figure 9-45 (a ) ECHINOIDS.

Echinoderm Sea Cucumbers Class Holothuroidea Have elongated bodies, and usually lie on 1 side Respiratory trees: a system of tubules located in the body cavity which accomplish gas exchange Sexes are generally separate

Figure 9-47 (a) SEA CUCUMBER.

Ecological Roles of Echinoderms Spiny skins deter most predators Predators of molluscs, other echinoderms, cnidarians, crustaceans crown-of-thorns sea star eats coral sea urchins destroy kelp forests Black sea urchins (Diadema antillarum) control algal growth on coral reefs Sea cucumber poison, holothurin, has potential as a medicine