Phylum Echinoderm

Echinoderm Mostly sessil life Adult has no head or brain Central nervous system with nerves radiating into arms All marine Echinodermata – spiny skinned

Cont… Most adults have pentaradial symmetry (all radial) Larvae have bilateral symmetry Separate sexes ; some hermaphrodites do exist Sea stars (not star fish); brittle stars; sea cucumbers; sea urchins, sand dollars, etc. ~ 8,000 to 10,000 species

Characteristics 1.Endoskeleton  an internal skeleton of calcium carbonate of tiny plates called ossicles- can be fused together 2. Pentaradial (Five part radially symmetrical  most have five arms)

Characteristics Cont… 3. Water vascular system  water system of connective canals and tube feet that are used for: locomotion, gas exchange, sensory, and capture food –Tube feet – muscular extension of water filled canals End is a sucker (attachment / locomotion)

Cont… 4. Coelomic circulation and respiration  body cavity functions as a simple circulatory system where particles move through the fluid- –Have skin gills  projections that are between the spines

Regeneration Many species autotomize, leaving predators with a nutritious souvenir while they escape Most sp. can regenerate from fragments

Sea Stars Most have 5 arms –Some have more (even 50) Carnivores (Bivalves ; snails ; barnacles ; etc.) –Ejects stomach inside out through mouth into the prey –Digestive enzymes are secreted and the digested food is carried into the glands for absorption –Stomach is then pulled back inside body

Feather Stars and Sea lilies Mouth is located on the upper surface Sessile but can detach & move around Attached to sea floor with a stalk Mouth & anus on upper surface

Brittle Stars Slender branched arms that readily break off & regenerate Move quicker than sea star Feed by raking in food with arms or trapping it with its tube feet

Sea urchins and Sand dollars Have the five distinct body parts Body shaped like a sphere (sea urchin) or a flattened disk (sand dollar) Lack arms Bodies covered with movable spines

Sea Cucumbers Softer Lack arms Live on ocean bottoms hiding in caves during the day Show bilateral symmetry Can eject parts of their internal organs (evisceration) to scare predators; regenerate these structures in days

HW 1. List the major echinoderm characteristics 2. Explain why some echinoderms would have bodies that are softer than others 3. Compare and contrast two examples of echinoderms.

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