Annelid Characteristics
- Well developed true coelom
- Segmented (reduced or lost in some)
- Complete digestive tract with regional specialization
- Closed circulatory system with respiratory pigments
- Well-developed nervous system
- Usually with lateral chaetae (spines) on each segment
- Marine, fresh water, and terrestrial environments
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Class Polychaeta — Sand & Clam Worms
Characteristics
- Numerous chaetae (setae) on segments
- Most have parapodia
- Often with tentacles, sensory, or feeding structures on head
- Some have chitinous jaws
- Lack clitellum
- Mostly marine; burrow, crawl over substrates, or live in tubes
- This class may be paraphyletic
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Sabellid Tube Worms, possibly Sabella sp., on Mangrove Roots, Belize
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Feather-duster Worm, Eudistyla sp.
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Parchment Worm, Chaetopterus sp., preserved specimen
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Scale Worm, Halosydna brevisetosa, CA
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Paddle Worm, possibly Phyllodoces sp., VA
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Polychaete Worm, possibly Glycinde sp., CA; and tubes of Spiral tube worms Spirorbis sp.
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Class Clitellata
Subclass Oligochaeta — Earthworms
Characteristics
- Few chaetae; lack parapodia
- Little structural specialization of head
- Presence of clitellum (forms muscus and egg cocoon)
- Mostly in terrestrial or fresh water environments
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Earthworm, Lumbricus sp., CA
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Dissected Earthworm, Lumbricus sp.
See also labeled photo.
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Earthworm, Lumbricus sp., stained cross-section slide, posterior to clitellum; 40x
See also labeled photo.
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Fresh-water worm, Dero sp.
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Tubifex sp. Worms, a fresh-water species
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Class Clitellata
Subclass Hirudinoidea — Leeches
Characteristics
- Segmenting less defined; body not divided by septa
- Clitellum present
- Lack setae or parapodia
- Have a posterior sucker and usually also an anterior sucker
- Mostly in fresh water, a few are marine and semi-terrestrial
- May be scavengers, predators, or external parasites
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Unidentified leech, showing ventral surface and suckers
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Leech, possibly Erpobdella sp., KY
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Class Echiura — Spoon Worms
Characteristics
- Unsegmented (most likely secondarily lost)
- Muscular, non-retractable proboscis with a groove (gutter)
- Many have chaetae or warty skin
- Long gut with with posterior anus
- Marine sediments: deposit or suspension feeders
- Formerly considered a separate phylum
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Innkeeper Worm, Urechis caupo, preserved specimen
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Phylum Sipuncula — Peanut Worms
Characteristics
- Unsegmented; schizocoelomate (true coelom) worms
- Anterior portion of body, introvert, can be fully withdrawn (as in photo)
- Fluid-filled tentacles around mouth
- Complete U-shaped gut
- Live in marine sediments
- Sometimes included within the Phylum Annelida
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Dissected Peanut Worm, Sipuncula sp.
See also labeled photo.
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Peanut Worm, Phascolosoma agassizzii, CA
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