Cervidellus serratus (Thorne, 1925) Thorne, 1937

(Fig. 2B)

Dimensions of 50 females: L = 0.38 mm (0.30-0.46); a = 15 (14-19); b = 3.2 (2.9-3.8); c = 12.5 (11-14); V = 65 (60 -67).

This species is very common and widespread on Spitzbergen. Body stout, tapering only slightly anteriorly, the diameter at the base of the oesophagus

1 Syn. S.incisa apud Loof, 1964.

being about twice the width of the lip region. Cuticle with coarse transverse striae about 2 \i apart in mid-body; anteriorly they become more spaced, being 2.5 -3.0 \i apart behind the lip region. Lateral field with two wings (three longitudinal grooves), about one-sixth of body diameter. Labial probolae acute, sclerotized, the axils bearing forward pointing acute processes. Prelabial probolae bifurcate over nearly half their length. Mouth cavity cephaloboid, details of rhabdions invisible as in the other cephaloboid species. Isthmus of oesophagus offset from corpus chiefly by alteration in the tissues. Terminal bulb well developed, with valves. Deirids not seen. The nerve ring surrounds the posterior end of the corpus. The excretory pore lies at level of anterior end of isthmus. Hemizonid immediately behind excretory pore, one to two annules long. Intestine with wide lumen. Vulva lips strongly protruding. Gonad cephaloboid, with spermatheca at the anterior flexure; the postvulvar part may show a double flexure or not. Dimensions of two intra-uterine eggs: 54-56 x 20 - 23 (x. In most specimens the posterior rudimentary gonad is relatively large as described by Thorne (1925); however, generally it is small, till one-half of body width, in specimens in which the anterior gonad is little developed. This condition is found generally in young slender females. In most older and fatter specimens the posterior gonad measures 1.3-1.8 body diameters. Rectum about as long as anal body diameter. Tail 1.8- 2.3 anal body widths long, regularly conoid with acute, in some specimens slightly offset, terminus.

Found in samples 17, 18, 20, 21, 23, 25, 26, 27, 30, 40, 42, 43, 44, 49, 53, 54, 55, 56, 60, 61, 62, 64, 65, 66 and 70.