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ECHINODERMS

ECHINODERMS. Wide variety of body plans stalked crinoids, starfish, sea urchins, sand dollars, sea cucumbers, and weird “sci-fi” stuff Not much range in size - few mm’s to 2 m Trophics – filter feeders, detritus feeders, grazers, predators, scavengers

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ECHINODERMS

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  1. ECHINODERMS

  2. Wide variety of body plans • stalked crinoids, starfish, sea urchins, sand dollars, sea cucumbers, and weird “sci-fi” stuff • Not much range in size - few mm’s to 2 m • Trophics – filter feeders, detritus feeders, grazers, predators, scavengers • No plankton and few nekton – heavy skeleton • Skeleton made of plates of single crystals of high Mg Calcite – sponge-like • Plates = ossicles, partly endoskeletal, come apart after death • Larvae bilaterally symmetrical, adults can be bilateral, pentameral, radial • None known to be fresh water or terrestrial, very few brackish – no discrete respiratory, excretory, or osmoregulatory system • All have water vascular system (hydraulic system filled with seawater)

  3. Water Vascular System • Opens to environment at • point covered by Madreporite • plate • Connects to ampullae which • are controlled by muscles to • control tube feet • Areas with openings for tube • feet = ambulacral areas • rest are interambulacral areas

  4. Echinoderms and chordates are deuterostomes • Tornaria larva – blastopore develops into anus, not mouth, • Coelom develops from pockets in endoderm • Means vertebrate and echinoderms closely related

  5. Phylum Echinodermata • “stalked” Pelmatozoans • Class Crinoidea (Camb-R) • Class Paracrinoidea (O-S) • Class Eocrinoidea (Camb-S) • Class Blastoidea (O-P) • Class Rhombifera (O-D) • Class Diploporita (O-D) • Carpoids • Class Stylophora (Camb-Carb) • Stars • Class Ophiuroidea (O-R) brittle stars • Class Asteroidea (O-R) seastars, star fish • Class Holothuroidea (Camb-R) sea cucumbers • Class Helicoplacoidea (Camb) • Class Edrioasteroidea (Camb-Carb) • Class Echinoidea (O-R) sea urchins, sand dollars

  6. Crinoids • 2 living groups: rare stalked and more common • feather stars. Most common fossil is stem segs. - • look like lifesavers. Anchored with holdfast.

  7. 2 living groups: rare stalked and more common • feather stars. Most common fossil is stem segs. - • look like lifesavers. Anchored with holdfast.

  8. Crinoid Evolution • Despite Burgess Shale form, really diversified in Ord. • Inadunates – rigid calyx, arms free above radials (no fixed brachials) • gave rise to flexibles (flexible calyxes, no pinnules on arms) and camerates (rigid calyx but multiple fixed brachials). • Originally co-existed with other pelmatozoa and archaic echinoderms. Diversified as other forms disappeared. Devonian extinction left only 5 living classes, Blastoids and Edrioasteroids. • Permian extinction wiped out paleozoic crinoids. Articulates (dorsal calyx reduced, v. flexible articulated arms) evolved from Inadunates in Triassic.

  9. Paracrinoids > • More like blastoids < Eocrinoids • Paraphyletic? May be ancestral to other pelmatozoans. Early ones had no stalk, stalk evolved later. Some may have been unattached and crawled

  10. Blastoids • Second most common stalked echinoderm. Unbranched arms (brachioles), 2 rows on either side of 5 ambulacral areas. Behind amb. areas were highly folded hydrospires (respiratory?) Pentremites is best known genus from Lower Carboniferous

  11. CYSTOIDS: • Long flexible stalk: attached or crawling. Irregular Theca, sometimes flattened

  12. Cystoids: Rhombifera > • Have pore rhombs with patterns of slits opening to hydrospire Cystoids: Diploporita > • Plates perforated by paired pores

  13. Carpoids • Asymmetrical, long aulacophore (feeding? Movement?). Opening near base is mouth? Anus?

  14. Ophiuroids • Long slender arms joined to body disc. Mouth center of bottom. Madreporite and anus on top. Most are cryptic or deep water. Detritivores

  15. Asteroids • Usually 5 arms, tube feet on base. Mouth in center. Digestive glands along arms. Protrusable stomach in center. Anus and madreporite on top of central area. Can regenerate. Slow moving predators.

  16. Holothuroids • Soft-bodied with dermal sclerites. Rest on sides or creep along seafloor, some burrow. Trap food w tentacle-like tube feet around mouth. One genus swims. All can spew intestnes and other internal organs.

  17. Helicoplacoids • Mouth on side. One ambulacral groove spirals to top, 2 more spiral down. May have been attached or free-living. Distinctive saddle-shaped plates

  18. Edrioasteroids • Small ( 1cm) disk-shaped attached forms. 5 ambulacral arms with tube feet, mouth in center. Anus on top, offcenter

  19. Echinoids • Most numerous Meso- and Cenozoic echinoderms. Fossilize well. Plates often tightly fused. Mouth usu at bottom, anus at top. Madreporite offcenter on top. 5 ambulacral areas. Those on top usu for respiration. Pedicellaria – stalks w pincer claws for protection. Spines (several sizes) – single xtal w ball/socket joint at test. • Primitive – radial symmetry – regular echinoids. Graze w jaws – Aristotle’s Lantern. (O-R)

  20. Echinoids • Irregular Echinoids – bilateral (Jr-R). Mouth to front, anus to back. Lots of small bristle-like spines. Burrowers. Many reduce ambulacral areas to top of test.

  21. Echinoids • Sand Dollars (Paleocene-R). Stick out of sediment shingle-like. Lunule reduces lift.

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