BIO 385 — Invertebrate Zoology
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Invertebrate Diversity
Clade Gnathifera:
Rotifers & Relatives

(Click on any image for larger version)

Phylum Rotifera — Wheel Animals

Characteristics

  • Very small, most <1 mm.
  • Varied, complex shapes
  • Anterior end has paired coronas lined with cilia
  • Many forms are sessile, attach via posterior foot
  • Mostly fresh water; a few are parasitic
  • Most are parthenogenic
  • Without Acanthocephalans, the group is paraphyletic
  • Clade that includes rotifers and acanthocephalans sometimes called Syndermata
Philodina
Fresh-water Rotifer, Philodina sp.; 100x
See also labeled photo.
Adineta
Fresh-water Rotifer, Adineta sp.
Squatinella
Fresh-water Rotifer, Squatinella sp.; collected Toleson, AZ
Monostyla
Fresh-water Rotifer, Monostyla sp.?; 100x
Euchlanis
Fresh-water Rotifer, Euchlanis sp.; 200x
Keratella
Fresh-water Rotifer, Keratella sp.; Phoenix, AZ
Brachionus
Fresh-water Rotifer, Brachionus sp.; Rio Salado, AZ; 200x
Synchaeta
Fresh-water Rotifer, Synchaeta sp.; Tolleson, AZ; 200x
Polyarthra
Fresh-water Rotifer, Polyarthra sp.; Rio Salado, AZ; 200x

Brachionus rotifer with egg next to it (bright field, 20x objective lens)
Brachionus rotifer feeding (bright field, 20x objective lens)

Acanthocephala — Spiny-headed Worms

Characteristics

  • Body cylindrical, usually with rings of small spines
  • Fluid-filled proboscis with hooks and spines
  • Lack gut; reduction of most organs
  • Pseudocoelom filled with large gonads
  • Intestinal parasites of vertebrates
  • Derived from within rotifer group
  • Formerly considered a separate phylum, but now is generally treated as a Class of rotifers

Acanthocephalan
Acanthocephalan, stained whole mount

NeoechinorhynchusAcanthocephalan
Spiny-headed worm, Neoechinorhynchus sp., preserved specimen

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
See also labeled photo.
Arrow Worm
Arrow worm, Sagitta sp., preserved specimen
Arrow Worm head
Sagitta sp., closeup of head; preserved specimen
This page last updated 20 December 2020 by Udo M. Savalli ()
Images and text © Udo M. Savalli. All rights reserved.