KINGDOM ANIMALIA
| SYSTEMATIC BIOLOGY |
KINGDOM ANIMALIA |
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| HOME | SYLLABUS | WEEKLY ASSIGNMENTS | J. SYSTEMATIC BIOLOGY | TAXA OF LIFE | |
| PHYLUM TARDIGRADA | |||||
INTRODUCTION TO THE TARDIGRADA
Tardigrada (tar-di-GRA-da) is formed from two Latin roots that mean "slow step" (slow - tardus; and step -gradus). The reference is to the very slow and deliberate movements of the eight stubby legs.
The tardigrades have a pudgy body with 4 pairs of slow-moving legs. Their behavior and appearance have earned them the common name water bear. Nielsen (2001), Brusca and Brusca (2003), Tudge (2000) and others place them squarely in the clade called the panarthropods. All agree that the tardigrades are the sister group to the arthropod clade. The onychophorans are a sister group to that complex.
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A. Hypisibius, preserved and stained. |
B. Scale-like segmented covering of a water bear. Also, note the claws at the ends of the stubby legs. |
C. An illustration of a water bear from the dorsal side and head toward the top. |
| Images taken from: A: This was taken from the Systematics Biodiversity collection. B: http://www.museums.org.za/bio/tardigrades/ C. http://biodidac.bio.uottawa.ca/ |
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SYNOPTIC DESCRIPTION OF THE PHYLUM TARDIGRADA
| 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). |
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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. Main body cavity pseudocoelomic Body Covering: Covered by mucopolysaccharide and protein cuticle. Support: Hydrostatic skeleton. Digestive System: Mouth terminal or subterminal. Feeding by a pair of buccal stylets and pharyngial pump. 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 and hind gut may function as Malpighian tubules. Nervous System: Bilobed brain connected by peribuccal cords to a double ventral nerve cord with ganglia in each leg segment. Simple eyes may be present. Endocrine System: None. B. Reproduction: Reproductive System: Dioecious. Females much more common. Males unknown in some species. Internal or external fertilization. Oviparous. Development: Cleavage is holoblastic 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. |
HIERARCHICAL CLASSIFICATION OF THE TARDIGRADA
| Ruppert and Barnes (1991) separate the phylum into two (or three) classes. However, most taxonomic systems recognize those groups only at the ordinal level. Thus, I use the system of Renaud-Morrant (1971, cited in Meglitsch and Schram 1991) that has a single class (that I call Targradida) and three orders. |
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CLASS TARDIGRADIDA (3 ORDERS)
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This page is maintained by Jack R. Holt. Last modified: 03/14/08.
