BIOL 1030 – TOPIC 12a LECTURE NOTES

Topic 12a: Deuterostomes I: Echinodermata and Hemichordata (Ch. 33)

  1. Deuterostomia (clade)
  2. defined primary by molecular evidence
  3. some defining developmental traits (see previous notes), but those can get fuzzy
  4. clade includes the following phyla that we will cover:
  5. Phylum Echinodermata (clade)
  6. Phylum Hemichordata (clade)
  7. Phylum Chordata (clade)
  1. Phylum Echinodermata - urchins, sea stars, sea cucumbers
  2. marine; ~7000 living species; in fossil record back to over 650 MYA
  3. name means “spiny skin”, reference to their endoskeleton
  4. calcium rich plates below skin
  5. living tissue when formed; usually fused into hard shell in adults
  6. pores in endoskeleton for water vascular system (madreporite, tube feet)
  7. water-vascular system - hydraulic system for moving, feeding
  8. water enters though madreporite, opening typically opposite mouth
  9. water from madreporite moves though stone canal
  10. water then enters the ring canal that encircles the esophagus
  11. radial canals extend from ring canal into the 5 body parts, establishing basic symmetry
  12. radial canals branch out into tube feet
  13. contraction of muscular sac (ampulla) at base of tube foot causes fluid to be forced into tube foot, extending it – used for movement
  14. pentaradially symmetrical - derived trait, larvae are bilaterally symmetrical
  15. coelom – relatively large; used for circulation and respiration
  16. asexual reproduction - many will regenerate if a broken part contains part of the central nerve ring, sometimes they will break on purpose
  17. sexual reproduction - form free-swimming larvae that are bilaterally symmetrical
  18. six classes, all apparently monophyletic
  19. Class Crinoidea - sea lilies and feather stars
  20. mouth and anus on same side
  21. 5-200+ arms, filter feeders
  22. primitive, sessile
  23. sea lilies – have calcareous stalk 15-30 cm long (20 m in some fossils)
  24. “living fossils”
  25. once much more commonone of the dominant forms of life in the marine fossil record of the Paleozoic era (both in numbers and size)
  26. feather stars - no stalk
  27. Class Asteroidea - sea stars or starfish
  28. 1 cm - 1 m across
  29. to 10,000 m deep
  30. groove runs along each arm bordered by rows of tube feet
  31. tube feet are like little suction cups and create an impressive force
  32. feed mainly on bivalves
  33. attach to either side of shell with tube feet
  34. wait until bivalve fatigues
  35. extrudes stomach into opening and digest prey
  36. Class Ophiuroidea - brittle stars
  37. look like sea stars, but more flexible, move via serpentine motion of arms, groove closed below arms
  38. tube feet used to capture small prey and as sensory structures
  39. Class Echinoidea - sea urchins and sand dollars
  40. no arms
  41. usually move via spines operated by tube feet
  42. vegetarians
  43. Class Holothuroidea - sea cucumbers
  44. elongate
  45. often with leathery skin
  46. mouth surrounded by 8-30 modified tube feet called tentacles
  47. other normal tube feet move animal
  48. will extrude their foul-smelling stomachs when frightened
  49. Class Concentricycloidea – sea daisies
  50. recently discovered
  51. no arms
  52. tube feet on edge of disc, instead of along radial lines
  1. Phylum Hemichordata (acorn worms)
  2. ~90 living species; all marine
  3. centimeter to meter size range; burrowing; proboscis, collar, and trunk
  4. name means “half chordates”; transitional group to phylum Chordata
  5. ciliated larvae resemble sea star larvae
  6. form a clade with Echinodermata (group called Ambulacraria)
  7. share with chordates:
  8. dorsal nerve cord as well as ventral nerve cord
  9. part of dorsal nerve cord hollow in some
  10. throat with pharyngeal gill slits

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