Scanning Electron Microscopical Observations of Pellioditis pellio (Nematoda: Secernentia)

Abstract

Scanning electron microscopical (SEM) observations were made on the surface topography of the lips, papillae, amphids, excretory pore, vulva, anus, caudal alae, cuticular bosses, and annular rings of larvae and adults of Pellioditis pellio. Cobb formula measurements and morphological characteristics agreed with those described previously for this species. SEM reveals for the first time: (1) fleshy appearance of the vulva; (2) spherical excretory pore; (3) crescent-shaped vent; and (4) biradial arrangement of oral papillae, lateral alae, and transverse bosses on the cuticle. Similarities to Caenorhabditis elegans are noted, suggesting that P. pellio may be a useful model for comparative neuroanatomical studies. According to Andrassy (1983), the correct name for Rhabditis pellio is Pellioditis pellio (Schneider, 1866). Morphology, based on light microscopy, and life history of P. pellio were described (Goodchild & Irwin, 1971; Hertwig, 1920; Smyth, 1976; Thorne, 1961), and some studies of reproduction and chemoattraction were conducted (Somers et al., 1977a,b). We report here for the first time surface anatomical features, both of larvae and adults of P. pellio, based on scanning electron microscopical observations. MATERIALS AND METHODS A lumbricid oligochaete, Apporectodea caliginosa (Savigny, 1827), recovered from soil in Long Beach, Los Angeles County, California, U.S.A., was cut into three pieces. Segments 20-40 were severed further into 2-3 mm pieces, which then were placed on 1% nutrient agar (Difco Laboratories, Detroit, Michigan, U.S.A.) in a 100 x 15-mm plastic Petri dish. The anterior and posterior pieces were fixed in 70% ethanol for taxonomic identification. After two days, living rhabditiform larvae appeared on the agar and were transferred to clean dishes. In 2-3 days posttransfer, numerous male and female adults, larvae, and eggs appeared on the surface of the agar. Thereafter, worms were subpassaged twice weekly by transfer into new dishes. Flavobacteria associated with the transferred worms provided nutrients. Goodchild & Irwin (1971) reported that Pellioditis pellio is dioecious, and that Rhabditis anomala and R. maupasi are thelyotokous and parthenogenetic, respectively. To determine the reproductive pattern of our isolate, 10 adult 1 We thank Professor George Poinar, Division of Entomology and Parasitology, University of California, Berkeley, California, for confirming the identification of Pellioditis pellio, and Professor E. G. Easton, Annelida Section of the British Museum for the identification of the annelid Apporectodea caliginosa. TRANS. AM. MICROSC. Soc., 109(1): 85-90. 1990. ? Copyright, 1990, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.162 on Thu, 11 Aug 2016 05:57:47 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC.