Paul B. Dye

Publication Date


Document Type


First Advisor

Engstrom, Norman A.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Tardigrada; Invertebrates--Classification


Consideration of the phylogenetic position of the Tardigrada based on scanning and transmission electron microscopy of certain morphological features of a species of Hypsibius. The morphology of a species of Hypsibius (Tardigrada, Order Eutardigrada, Family Macrobiotidae) is described on the basis of electron microscopy. The body cuticle is two layered; the structure of the cuticle lining the pharynx is simpler than that of the body cuticle, as is the structure of the sclerous claws, macroplacoids, and stylets. The epidermis is truly cellular and lacks microvilli. The musculature is organized into individual strands composed of single cells or small groups of cells, and the points of muscle attachment at the body wall have a much simpler structure than those of arthropods. The body wall, muscles, and internal organs are unlined by peritoneum, suggesting that the spacious body cavity may be a pseudocoelom. The bulbous sucking pharynx is composed of apical myoepithelial cells. Posterior to this pharynx, the structure of the gut wall varies, but its cells are always highly vacuolated. The structure of two special types of glands, the buccal glands and the claw glands, is described, the most distinguishing feature of both being the large amount of rough endoplasmic reticulum they contain. Comparisons of four morphological characteristics: the nature of the body cavity, the composition of the cuticle, the fine structure of muscle attachment points, and the condition of the muscular pharynx, show that tardigrades are quite distinct from arthropods, and instead resemble pseudocoelomates in many ways.


Includes bibliographical references.


vi, 38 pages




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