BIO 385 — Invertebrate Zoology
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Invertebrate Diversity
Phylum Annelida

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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

Class Polychaeta
Subclass Errantia — Free-swimming Worms

Characteristics

  • Numerous chaetae (setae) on segments
  • Most have well-developed parapodia
  • Most have sensory tentacles and eyes on head
  • Many have chitinous jaws
  • Lack clitellum
  • Marine or brackish waters
  • Mobile (errant): crawl over substrates or swim
  • The monophyly of this group is not certain
 Scale Worm
Scale Worm, Halosydna brevisetosa, CA 		Calif Fireworm
California Fireworm, Pareurythoe californica; La Jolla, CA 		Bristle worm
Common Bristleworm, Linopherus sp.
12-Scale Worm
Twelve-scale Worm, Lepidonotus squamatus, CT 		12-Scale Worm
Dried Bristle Worm specimen, Chloeia sp. 		Dorvilleid Worm
Dorvilleid Worm, possibly Dorvillea sp.
blood Worm
Blood Worm, Glycera sp., La Jolla, CA 		Oenonid Worm
Lumbrinereid Worm, possibly Lumbrinereis sp. 		Cambrian Annelids
Two models of likely polychaete annelids from the Cambrian Period: Canadia (left) & Burgessochaeta (right), roughly to scale with one another.
Leafy Paddlewormm
Leafy Paddleworm, Phyllodoce medipapillata; La Jolla, CA 		Green Iridescent Worm
Green Iridescent Worm, Arabella iricolor, La Jolla, CA 		Sea Nymph epitoke
Sea Nymph (Nereis sp.?) epitoke (pelagic sexual) stage; La Jolla, CA

Class Polychaeta
Subclass Sedentaria — Tube and Fan-headed Worms

Characteristics

  • Parapodia and chaetae often reduced or lost
  • Most are sedentary, living in burrows or secreted tubes
  • Many with feathery tentacles for feeding
  • Mostly filter feeders or suspension feeders
  • This subclass is probably paraphyletic
Xmas Tree Worms
Christmas Tree Worms Spirobranchus giganteus; two color variations 		Sabellid Tube Worm
Feather-duster Worm, Eudistyla sp. 		Feather-duster Worms
Red Tube Worm, Serpula sp.
Feather-duster Worms
Sabellid Tube Worms, possibly Sabella sp., on Mangrove Roots, Belize 		Spiral Tubeworms
Spiral Tubeworms, Pileolaria sp. (note also acoel flatworm in lower left) 		Spionid Tube Worm
Spionid Tube Worm 		Sandcastle Worm tubes
Sand-castle Worm tubes, Phragmatopoma californica; Calif.
Bispira Fan Worm
Fan Worm, Bispira sp.? 		Spaghetti Worm
Spaghetti Worm, Terebella californica?, tentacles. The numerous fine tentacles are used to locate small food particles. 		small Spaghetti Worm
Small Unidentified Spaghetti Worm; Calif. 		Giant Tube Worm
Giant Tube Worm, Riftia pachyptila, from deep-sea volcanic vents; preserved specimen

Polychaetes of Uncertain Relationships

Characteristics

  • Polychaete worms that do not fit into the other groups
  • Parchment worms (Family Chaetopteridae) are perhaps the most basal of the annelid worms
  • Aelosomid worms were thought to be oligochaetes due to their fresh-water habits, but may be polychaetes instead
 Parchment Worm
Parchment Worm, Chaetopterus sp., preserved specimen 		Aeolosoma worm
Freshwater worm Aeolosoma sp.

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
Earthworm Dissection
Dissected Earthworm, Lumbricus sp.
See also labeled photo. 		Earthworm
Earthworm, Lumbricus sp., CA 		Dero
Fresh-water worm, Dero sp.
Earthworm
Earthworm, Lumbricus sp., stained cross-section slide, posterior to clitellum; 40x
See also labeled photo. 		Tubifex Worms
Tubifex sp. Worms, a fresh-water species 		Stylaria
Fresh-water worm, Stylaria sp.

Class Clitellata
Subclass Hirudinea — 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
Leech slide
Leech, wholemount slide
See also labeled photo. 		Helobdella Leech
Freshwater leech Helobdella sp.; Phoenix, AZ 		Leech
Predatory leech, probably Nephelopsis obscura, showing ventral surface and suckers
Erpobdella Leeches
Scavenging leech, Erpobdella sp., KY

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
Innkeeper Worm
Innkeeper Worm, Urechis caupo, preserved specimen 		Coprinoscolex fossil
Fossil Spoon Worm, Coprinoscolex ellogimus; 300 Ma, IL

Class Sipuncula — Peanut Worms

Characteristics

  • Unsegmented (secondarily lost?)
  • Anterior introvert can be fully withdrawn
  • Fluid-filled tentacles around mouth
  • Gut U-shaped; anus near introvert
  • Live in marine sediments
  • Formerly considered a separate phylum
Sipunculan Dissection
Dissected Peanut Worm, Sipuncula sp.
See also labeled photo. 		Peanut Worm
Peanut Worm, Phascolosoma agassizzii, CA 		Peanut Worm
Peanut Worm, Phascolosoma sp.
This page last updated 13 May 2023 by Udo M. Savalli ()
Images and text © Udo M. Savalli. All rights reserved.