ANNELIDA (II): Oligochaeta, Hirudinea (Annelida study images;
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a) remarkably little morphological diversity; mainly detritivores
b) Darwin estimated they move 18 tons of soil/acre/year to surface
c) 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 occur in only a few segments; a clitellum secretes the cocoon in which eggs are laid
d) burrow via retrograde peristaltic waves of body-wall muscles
a) share 5 traits with oligochaetes: no parapodia; no prostomial appendages; hermaphroditic; gonads occur in only a few segments; a 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) several adaptations for blood feeding in ectoparasitic forms:
Copyright (c) 2004 by A. Richard Palmer. All rights reserved.
(revised Feb. 1, 2004)