DESCRIPTION OF THE PHYLUM GASTROTRICHA (METSCHNIKOFF 1865)
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GASTROTRICHA LINKS
| 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. |
| INTRODUCTION TO THE GASTROTRICHA The gastrotrichs are small creeping animals that live in marine and freshwater sediments and substrates. Typically, the cuticle (text with tooltip) Cuticle is an acellular covering that is secreted by the epithelium in animals. It also is the waxy material, made of cutin, on the outside of plants. is developed into a covering of scales and spines (Figures 1-3). Many have distinctive tails, either long or bifrucate (Figure 4), and move over the substrate smoothly by ciliated epithelium (text with tooltip) Epithelium is a tissue that covers (or lines) a structure. Ciliated epithelium is made of epithelial cells that may have one or more flagella (=cilia) inserted into it. It is the chief means of locomotion for many invertebrates. . They resemble rotifers or large ciliates with which they often occur. They feed with an evertible proboscis (text with tooltip) A proboscis is a tube or tubular process that occurs on the head or the anterior of the gut. that retracts into a cavity similar to a rhynchocoel (text with tooltip) A rhynchocoel is a fluid-filled body cavity (coelom? pseudocoelom?) into which the nemertene evertible proboscis retracts. , dorsal to the intestine. Valentine (2004) considers the gastrotrichs to be the sister group to the rotifers+acanthocephala. Giribet et al. (2007) place them together with the flatworms, rotifers, and gnathustomulids in a group called Platyzoa. Unlike the Trochozoa, the Platyzoa is weakly supported as a clade and it has no obvious morphological apomorphy (Dunn et al. 2008; Edgecombe et al. (2011). We have followed Edgecombe et al. (2011) and placed the Gastrotricha as a sister to Platyhelminthes + Gnathifera (see Figure 5). |
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| FIGURE 1. A light micrograph of Chaetonotus, a common spiny gastrotrich. Image from http://www.gastrotricha.unimore.it/picturegallery.htm | FIGURE 2. An SEM micrograph of Chaetonotus that allows the visualization of the spines. Image from http://www.gastrotricha.unimore.it/picturegallery.htm | FIGURE 3. The scaly nature of the cuticle can be seen in this taxon with short spines. Image from http://www.gastrotricha.unimore.it/picturegallery.htm | FIGURE 4. A photomicrograph that illustrates the typical bifurcate tail of gastrotrichs. Image from http://www.gastrotricha.unimore.it/picturegallery.htm |
 | FIGURE 5. A figure showing the sister relationship between the Gastrotricha and the Platyhelminthes + Gnathifera clade within the Platyzoa (Pl). P = Protostomata |
| LITERATURE CITED Barnes, R. D. 1980. Invertebrate Zoology. Saunders College/Holt, Rinehart and Wilson, Philadelphia. Barnes. R. S. K. 1984a. Kingdom Animalia. IN: R. S. K. Barnes, ed. A Synoptic Classification of Living Organisms. Sinauer Associates, Inc., Sunderland, MA. pp. 129-257. Brusca, R. C. and G. J. Brusca. 2003. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass. Buchsbaum, R. 1938. Animals Without Backbones, An Introduction to the Invertebrates. The University of Chicago Press. Chicago. Dunn, C. W., A. Hejnol, D. Q. Matus, K. Pang, W. E. Browne, S. A. Smith, E. Seaver, G. W. Rouse, M. Obst, G. D. Edgecombe, M. V. Sørensen, S. H. D. Haddock, A. Schmidt-Rhaesa, A. Okusu, R. M. Kristensen, W. C. Wheeler, M. Q. Martindale, and G. Giribet. 2008. Broad phylogenomic sampling improves resolution of the animal tree of life. Nature. 452: 745-749. Edgecombe, G. D., G. Giribet, C. W. Dunn, A. Hejnol,R. M. Kristensen, R. C. Neves, G. W. Rouse, K. Worsaae, and M. V. Sorensen. 2011. Higher-level metazoan relationships: recent progress and remaining questions. Organisms Diversity and Evolution. DOI 10.1007/s13127-011-0044-4. Giribet, G., C. W. Dunn, G. D. Edgecombe, and G. W. Rouse. 2007. A modern look at the Animal Tree of Life. Zootaxa. 1668: 61-79. Hickman, C. P. 1973. Biology of the Invertebrates. The C. V. Mosby Company. Saint Louis. Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York. Meglitsch, P. A. and F. R. Schramm. 1991. Invertebrate Zoology. Oxford University Press, New York, Oxford. Metschnikoff (Ме́чников), E. 1865. Über einege wennig bekannte niedere Thierformen. Zeitschrift für Wissenschaftliche Zoologie. 15: 450-463. Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford. Ruppert, E. E. and R. D. Barnes. 1994. Invertebrate Zoology. 6th edition. Saunders. Ft Worth, TX. Ruppert, E. E., R. S. Fox, and R. D. Barnes. 2004. Invertebrate Zoology: A Functional Evolutionary Approach. Seventh Edition. Thomson, Brooks/Cole. New York. pp. 1-963. Storer, T. I. and R. L. Usinger. 1965. General Zoology. 4th Edition. McGraw-Hill Book Company. New York. Tudge, C. 2000. The Variety of Life, A Survey and a Celebration of all the Creatures That Have Ever Lived. Oxford University Press. New York. |
| By Jack R. Holt and Carlos A. Iudica. Last revised: 04/10/2013 |
