ANNELIDA (II): Oligochaeta, Hirudinea (Annelida study images; |
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 occur in only a few segments; a clitellum secretes the cocoon in which eggs are laid
c) 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
TWO MINOR PROTOSTOME PHYLA (click on tree to see full cladogram) |
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
a) reach large size in vent communities; make long chitinous tubes
b) 3 body regions: i) forepart with tentacles, ii) trunk, iii) large segmented opisthoma (fully segmented coelom; setae in setal sacs)
c) larvae have a complete gut like an annelid worm; lack a gut as adults but possess symbiotic bacteria in tentacles or trophosome
d) linked to annelids by features of opisthoma
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