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SYSTEMATIC BIOLOGY					KINGDOM ANIMALIA
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PHYLUM GASTROTRICHA

INTRODUCTION TO THE GASTROTRICHA

Gastrotricha (gas-tro-TRIK-a) is made of two Greek roots that mean hairy stomach [stomach -gastros (γαστρός); and hair -tricha (τρίχα)]. The reference is to the long hair-like spines that terminate scales on the trunk of the animal.

The gastrotrichs are small creeping animals that occur in marine and freshwater sediments and substrates. Typically, the cuticle is developed into a covering of scales and spines (Figures A-C). Many have distinctive tails, either long or bifrucate (Figure D), and move over the substrate smoothly by ciliated epithelium. They resemble rotifers or large ciliates with which they often occur.

A. A light micrograph of Chaetonotus, a common spiny gastrotrich.

B. An SEM micrograph of Chaetonotus that allows the visualization of the spines.

C. The scaly nature of the cuticle can be seen in this taxon with short spines.

D. A photomicrograph that illustrates the typical bifurcate tail of gastrotrichs.

Images taken from:
A-D: http://www.gastrotricha.unimore.it/picturegallery.htm

SYNOPTIC DESCRIPTION OF THE GASTROTRICHA

The following information came from Margulis and Schwartz (1998), Buchsbaum (1938), Barnes (1980), Barnes (1984), Brusca and Brusca (2003), Hickman (1973), Storer and Usinger (1965), and Tudge (2000).

I. SYNONYMS: gastrotrichs.

II. NUMBER: >450 species known.

III. PHYLUM CHARACTERISTICS:

A. Structure

Symmetry: Bilateral

Body Cavity: Problematic, probably acoleomic. Organ systems in parenchymatous mesoderm. Evertible proboscis in a cavity similar to a rhynchocoel, dorsal to the intestine.

Body Covering: Ciliated epithelium, particularly on ventral side. One flagellum (cilium) per epidermal cell as in Gnathostomulida. Surface covered with a cuticle that has characteristic scales or spines and adhesive tubes for temporary attachment.

Support: Hydrostatic skeleton.

Digestive System: Complete food tube with mouth (muscular pharynx) and anus.

Circulatory System: Blood vessel system in parenchymal mesoderm.

Locomotion: Ciliated epithelium and muscular contractions.

Excretory System: Protonephridial excretory canals.

Nervous System: Two anterior ganglia with 2 major lateral nerves. Anterior sense organs such as photoreceptors, bristles, and sensory pits.

Endocrine System: None.

B. Reproduction:

Reproductive System: Hermaphroditic, some parthenogenetic. Oviparous.

Development: Zygote develops by bilateral radial cleavage; no distinctive larval stage.

C. Ecology: Freshwater, marine, free living, usually benthic.

HIERARCHICAL CLASSIFICATION OF THE GASTROTRICHA

This taxonomy follows the system of Brusca and Brusca (2003) who have defined only a single class (Gastrotrichida) and two orders.

CLASS GASTROTRICHIDA (2 ORDERS)

Chaetonotus, Tetranchyroderma, Dactylopodula, Macrodasys, Platydasys, Pleurodasys, Turbanella, Urodasys, Neodasys, Aspidophorus, Dasydytes, Lepidodermella.

This page is maintained by Jack R. Holt. Last modified: 01/05/08.