Zoology 250 Lecture 21
Phylum ANNELIDA: Oligochaeta, Hirudinea
- 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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