Unit 6 Echinodermata Sea Stars Sea Urchins Sea Cucumbers Brittle Stars

Echinodermata (spiny + skin + to bear) Phylum Echinodermata (spiny + skin + to bear) Echinoderms are an ancient species that began evolving nearly 600 mya. Fossil evidence shows that nearly 12 to 18 Classes have gone extinct.

Adults Pentaradial; larva bilateral Calcareous exoskeleton Characteristics of Echinodermata ~7000 species All Marine Pentaradial symmetry Adults Pentaradial; larva bilateral Calcareous exoskeleton Water vascular system (locomotion, attachment, feeding) Complete digestive tract Nervous system Close evolutionary relationships with Chordata -both deuterostomes Echinoderms evolved from a bilateral ancestor. -Larva form still bilateral

Skeleton: Calcium carbonate plates called ossicles Some ossicles are modified into spines for defense.

Water vascular system: Sea water filled canals with extensions on the ventral surface called tube feet. Tube Feet: Extensions of the canal system used for locomotion, feeding and sensing Environment.

5 arm water vascular system

Class Asteroidea (star + in the form of) ~ 1500 species Marine benthic (substrate) environments 5 arms radiate from central disc Mouth center of ventral surface Spines on aboral surface

Pedicellariae: Pincer-like structures on the aboral surface Capture prey Keep sessile organisms from attaching(sponge, coral)

Ambulacral groove: Several ossicles on the ventral surface. Forms a groove that runs the length of the arm. -Paired rows of tube feet found in this groove.

Feed on gastropods, bivalves, crustaceans and coral. Nutrition: Feed on gastropods, bivalves, crustaceans and coral. 2 stomach regions: Oral stomach (cardiac)- larger, responsible for beginning digestion. Aboral stomach (pyloric) – smaller, gives rise to digestive ducts, final digestion and absorption. -Some ingest whole prey -Some digest externally Excretion occurs through pores in the aboral surface as well as tube feet.

Nervous system: Nerve ring encircles mouth. Radial nerves radiate to arms. Sensory receptors in tube feet, especially terminal feet.

Reproduction: Asexual- Can completely regenerate from just one section of an arm if it contains just a portion of the central disc. Sexual- Dioecious Not Dimorphic 2 gonads in each arm. Gonopores release gametes externally.

Class Ophiuroidea ( Snake + Tail + in the form of) Brittle stars ~2000 species. Largest of all Echinoderm Classes

Morphological differences: Most between 1-3cm in size Madreporite on oral surface Use arms (modified ossicles) for locomotion -not tube feet Regeneration: Autotomy (self + to cut) - can lacerate its own appendage to escape predation, then regenerate.

Class Echinoidea (spiny + in the form of) ~1000 species Sand Dollars live on soft sand or mud. Sea Urchins Live on hard surfaces

Urchin spines: Spines may be hollow and contain venom. Spines are hinged and movable. Spines used to push Urchin, tube feet used to pull Aristotle’s Lantern: Complex chewing apparatus with 35 ossicles and muscles.

Class Holothuroidea (Sea Cucumber + In the form of) ~1500 species 10-30 cm No arms Grow horizontally along oral-aboral axis.

Nutrition: Elongated tube feet modified into tentacles called “feeding tentacles”. Crawl ocean floor collecting debris, digesting organic material, eliminating inorganic waste. Large ossicles form chewing ring around mouth

Respiratory trees: Branching tubes that carry sea water throughout the body, absorbing O2 and excreting waste. Evisceration: Expulsion of respiratory tree, gonads, and digestive tract. (sticky & toxic) Organs regenerate

Class Crinoidea (lily + in the form of) Sea Lilies Feather Stars ~ 630 species Most primitive - LCA of all Echinoderms 500-600 mya (early Paleozoic Era)

Calyx- a set of ossicles that connect the crown/arms with the stalk.

Class Concentricycloidea: (Having a common ancestor + Circle) Sea Daisy ~1 cm in size Unsure of precise ancestry to Echinoderms