--------------- Wed. March 11 (cont.)-------------
• 1) Class Oligochaeta (earthworms & relatives, approx. 3,000 spp)

  a) remarkably little morphological diversity; mainly detritivores

  b) differ from polychaetes in 8 ways: no parapodia; few setae; highly compartmentalized coelom throughout class; small, simple prostomium (no sensory structures); no eversible proboscis; entirely hermaphroditic; gonads in only a few segments; clitellum that secretes cocoon for laying eggs

  c) burrow via retrograde peristaltic waves of body-wall muscles

  --------------- Fri. March 13 -------------

• 2) Class Hirudinea (leeches, approx. 500 spp)

  a) share 5 traits with oligochaetes: no parapodia; no prostomial appendages; hermaphroditic; gonads in few segments; clitellum (seasonal)

  b) differ from oligochaetes in 5 ways: no setae; coelom not compartmentalized; body dorso-ventrally compressed; anterior and posterior suckers (formed by fusion of segments); constant number of body segments (33 or 34 throughout class)

  c) some have eversible proboscis or jaws

  d) includes parasitic and free living groups

  ---

• 1) Phylum Echiura (marine innkeeper worms, approx. 100 spp)

  a) body of two distinct parts: trunk, large flap-like proboscis

  b) have one large coelom, coiled gut with terminal mouth & anus

  c) linked to annelids by: annelid cross, paired setae in setal sacs

• 2) Phylum Pogonophora (marine beard worms, approx. 100 spp)

  a) live mainly in deep sea; reach large size in vent communities

  b) body of three distinct parts: forepart with tentacles, trunk, large segmented opisthoma

  c) lack a gut at any stage in life cycle; possess symbiotic bacteria

  d) linked to annelids mainly by features of opisthoma (segmented, compartmentalized coelom; setae in setal sacs) but also by spiral cleavage

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