Internal Anatomy of Meiopriapulus fijiensis (Priapulida)

Abstract

Scanning and transmission microscopical analyses of the major organ systems of Meiopriapulus fijiensis were performed. The most important findings included the presence of an epithelium-lined multichambered system surrounding a portion of the foregut, a complex foregut structure with an eight-ridged pattern extending into the polythyridium, and a gland located anteriorly in the midgut. The ultrastructural organization of the protonephridia and the ovaries is more similar to macrobenthic priapulids than to members of other meiobenthic taxa. The flagellated spermatozoa are of a primitive type, having a globular nucleus, a cap-shaped acrosome, and four mitochondria. This suggests external fertilization, which stands in contrast to internal fertilization known for Tubiluchus. Our knowledge of the ultrastructure of meiobenthic Priapulida is almost exclusively based on the analysis of Tubiluchus philippinensis van der Land, 1985 (see Alberti & Storch, 1983, 1986, 1988, 1989; Storch & Alberti, 1985a,b). Recently, some organ systems of the sedentary meiobenthic species Maccabeus tentaculatus Por, 1973 were analyzed by means of scanning and transmission electron microscopy (Wolter, 1987). Generally, there is a striking similarity between these two genera at the ultrastructural level. However, an analysis of the integument of Meiopriapulus fijiensis Morse, 1981, the only species of the third genus of meiobenthic Priapulida, revealed some basic differences in fine structure (Storch et al., 1989). The purpose of the present paper is to compare the ultrastructure of internal organs of Meiopriapulus fijiensis with corresponding organs of Tubiluchus and Maccabeus. Attention is focused only on features differing from the latter two. MATERIALS AND METHODS Living specimens of Meiopriapulus fijiensis were collected from the infralittoral zone at Korolevu Beach on Viti Levu, Fiji, and transported to Friday Harbor Laboratories, University of Washington, where they were maintained in seawater among sand grains in glass bowls at ambient room temperature. The authors gratefully acknowledge use of the priapulids collected in Fiji by Dr. G. Pauley and subsequently fixed for TEM by Mr. E. Meyh6fer (both of the University of Washington). We also acknowledge the technical assistance of Ms. R. Mummert (Heidelberg) and Mr. H. P. Dreyer (Kiel), and the field assistance of Ms. N. Helm (former Peace Corps volunteer, Western Samoa). This study was supported by a NATO Grant for Collaborative Research to V. Storch and R. P. Higgins, and a grant to R. P. Higgins (for field work in Fiji) from the Smithsonian Research Opportunities Fund. For M. P. Morse, this is Contribution No. 176, Marine Science Center, Northeastern University. TRANS. AM. MICROSC. Soc., 108(3): 245-261. 1989. ? Copyright, 1989, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.104 on Wed, 28 Dec 2016 18:06:34 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC.