• 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

• 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 as adults, larvae have a complete gut like an annelid worm; possess symbiotic bacteria

  • d) linked to annelids by features of opisthoma (fully segmented coelom; setae in setal sacs) and spiral cleavage

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