DEVELOPMENT, ULTRASTRUCTURE AND FUNCTION OF THE PHARYNX OF HALOBIOTUS-CRISPAE KRISTENSEN, 1982 (EUTARDIGRADA)

The ultrastructure of the adult pharynx of the eutardigrade Halobiotus crispae is described for the active, sexually mature summer form as w ell as for the winter form known as pseudosimplex 1. The total number of cells is 54: 27 muscle cells, 12 apical cells, nine nerve cells and six buccal tube cells. The development of the pharynx is described on the basis of five ontogenetic stages. Three of them are reconstructed three-dimensionally with the help of computer techniques. The number of cells composing the pharynx remains constant from an early embryolo gical stage and each cell can be traced and recognized in the adult ph arynx. The findings regarding the ultrastructure of the pharynx are co mpared to previous descriptions. A hypothesis regarding the coordinate d function of the organ and a preliminary attempt to define the plesio morphic condition of the tardigrade pharynx are presented. (C) 1997 Th e Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd .