SYNOPTIC DESCRIPTION OF THE PHYLUM TARDIGRADA (SPALLANZANI 1777)
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TARDIGRADA LINKS
| The following information came from Margulis and Schwartz (1998), Buchsbaum (1938), Barnes (1980), Barnes (1984), Brusca and Brusca (2003), Hickman (1973), Meglitsch and Schramm (1991), Ruppert and Barnes (1991), Storer and Usinger (1965), and Tudge (2000). |
I. SYNONYMS: tardigrades, water bears.
II. NUMBER: >400 species known.
III. PHYLUM CHARACTERISTICS:
- A. Structure
- Symmetry: Bilateral
- Body Cavity: True coelom enterocoelic; degenerates to small cavities around the gonads (text with tooltip) Gonads are sex glands in animals. Ovaries produce eggs and testis produce sperm. . Main body cavity pseudocoelomic
- Body Covering: Covered by mucopolysaccharide and protein 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. .
- Support: Hydrostatic skeleton.
- Digestive System: Mouth terminal or subterminal. Feeding by a pair of buccal stylets (text with tooltip) Buccal stylets are needle-like feeding structures in tardigrades. and pharyngial pump (text with tooltip) Pharyngial pump is a muscular pump connected to the buccal styles in tardigrades. It is used for sucking plant cell contents in feeding. . Food tube complete with fore and hind gut. Anus terminal.
- Circulatory System: Absent.
- Locomotion: Animals move by 4 pairs of stubby, unjointed legs that terminate in 2-11 claws.
- Excretory System: Pouches at the junction of the fore (text with tooltip) The foregut (also called the stomodaeum) is the anterior portion of the gut that is lined with ectoderm. and hind gut (text with tooltip) The hindgut is the posterior portion of the gut that is lined by ectoderm. may function as Malpighian tubules (text with tooltip) Malpighian tubules are excretory organs in arthropods. They are fine tubules attached at the hind gut and bathed in the haemolymph (blood) of the haemocoel from which they remove nitrogenous waste. .
- Nervous System: Bilobed brain connected by peribuccal cords to a double ventral nerve cord with ganglia in each leg segment. Simple eyes (text with tooltip) An ocellus (ocelli, pl.) is a simple eye or eyespot characteristic of many invertebrate groups. may be present.
- Endocrine System: None.
- B. Reproduction:
- Reproductive System: Dioecious (text with tooltip) Dioecious organisms have separate male and female individuals. . Females much more common. Males unknown in some species. Internal or external fertilization. Oviparous (text with tooltip) An oviparous (adj.) animal is one that releases eggs in its life cycle. They may be fertilized internally or externally. .
- Development: Cleavage is holoblastic (text with tooltip) Holoblastic (adj.) describes the type of cleavage in which the zygote divides by complete cytokinesis. but irregular. All cells of adult produced in the egg. Animal increases in size by water uptake (not mitosis) after hatching. No larval stages.
- C. Ecology: Inhabit water films in interstices of bottom sediments, soil, mosses, and lichens. One from hot springs in Japan. Feed on body fluids of an array of small animals, mosses and lichens.
| LITERATURE CITED Bertolani, R., R. Guidetti, I. Jonsson, T. Altiero, D. Boschini, and L. Rebecchi. 2004. Experiences with domancy in tardigrades. J. Limnol. 63(Suppl. 1): 16-25. Brusca, R. C. and G. J. Brusca. 2003. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass. Budd, G. E. 2001. Tardigrades as ‘Stem-Group Arthropods’: The evidence from the Cambrian fauna. Zool. Anz. 240: 265-279. Esser, R. P. 1990. Tardigrades attacking nematodes. Nematology Circular No. 177. Fla Dept. Agric. and Consumer Serv. pp. 4. Hickman, C. P. 1973. Biology of the Invertebrates. The C. V. Mosby Company. Saint Louis. Jönsson, K. I., E. Rabbow. R. O. Schill, M. Harms-Ringdahl, and P. Rettberg. 2008. Tardigrades survive exposure to space in low Earth orbit. Current Biology. 18(17): R729-R731. 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. Nicholas, W.L. 2001b. The pseudocoelomate Ecdysozoa. In: Anderson, D.T., ed. Invertebrate Zoology. Oxford University Press. Oxford, UK. pp. 98-119. Nelson, D. R. 2002. Current status of the Tardigrada: evolution and ecology. Integ. and Comp. Biol. 42: 652-659. Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford. Pechenik, J. A. 2005. Biology of the Invertebrates. McGraw-Hill. New York. Romano, F. A. 2003. On water bears. Florida Entomologist. 86(2): 134-137. Ruppert, E. E. and R. D. Barnes. 1994. Invertebrate Zoology. 6th edition. Saunders. Ft Worth, TX. Schill, R. O., G. H. B. Steinbruck, and H.-R. Kohler. 2004. Stress gene (hsp70) sequences and quantitative expression in Milnesium tardigradum (Tardigrada) during active and cryptobiotic stages. Journal of Experimental Biology. 207: 1607-1613. Telford, M. J. S. J. Bourlat, A. Economou, D. Papillion, and O. Rota-Stabelli. 2008. The evolution of Ecdysozoa. Phil. Trans. R. Soc. B. 363: 1529-1537. 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: 02/03/2013 |
