BIO 385 Invertebrate Zoology
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Invertebrate Diversity
Minor Phyla of Uncertain Relationship

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Phylum Gastrotricha

Characteristics

  • Minute (<1 mm) unsegmented animals
  • Body moderately elongated, somewhat flattened
  • Epidermis with plates or spines
  • Cilia on ventral surface
  • Sensory bristles on head
  • Typically have "bowling pin" shape: rounded head with slight neck constriction
  • Many have a pair of posterior projections (caudal furca)
  • In fresh water and marine sediments
  • Phylogenetic relationships uncertain
Lepidodermella Gastrotrich
Fresh-water gastrotrich, Lepidodermella sp.
Chaetonotus Gastrotrich
Fresh-water gastrotrich, Chaetonotus sp.
Macrodasys Gastrotrich
Marine gastrotrich, Macrodasys sp.

Phylum Chaetognatha Arrow Worms

Characteristics

  • Elongate, streamlined bodies
  • Lateral & caudal fins supported by rays
  • Mouth surrounded by grasping spines
  • Complete gut
  • Longitudinal but not circular muscles
  • Pelagic marine predators
Arrow Worm
Sagitta sp., stained whole mount
Arrow Worm
Sagitta sp., closeup of head; stained whole mount
Arrow Worm
Spadella cephaloptera (Encyclopedia Britannica 1911)

Phylum Entoprocta (Kamptozoa)

Characteristics

  • Solitary or colonial, often stalked
  • Tiny size (usually <2 mm)
  • Ring of ciliated tentacles surround mouth and anus
  • U-shaped gut
  • This phylum may not be represented in lab

Entoproct
Solitary Entoproct, possibly Loxosoma sp., with bud

Entoproct
Solitary Entoproct, possibly Loxosoma sp., tentacles retracted

Entoproct
Nodding Head Entoproct, possibly Barentsia sp.; CA
This page last updated 19 March 2017 by Udo M. Savalli ()
Images and text Udo M. Savalli. All rights reserved.