Description of two new species of the genus Chiloplacus Thorne, 1937 (Rhabditida: Cephalobidae) from Israel and Senegal

Chiloplacus, C. membranifer sp. n. and C. similis sp. n., are described from arid habitats in Israel and Senegal, respectively. Both new species share the unique character of an asymmetrical development of the lateral fi eld at the level of vagina and a left-ventrosublateral position of the vulval opening differentiating them from all other species of Chiloplacus. Females of the new species can be separated from each other by body length (560-654 vs 778-998 µm) and many other morphometric characters like body diameter (21.0-27.0 vs 25.5-37.0 µm), neck length (161-172 vs 205-257 µm), tail length (28.0-31.0 vs 41.5-49.0 µm), anal body diameter (13-16 vs 18-29 µm), lip region diameter (7.5-9.0 vs 10.0-12.0 µm), corpus length (105-124 vs 149-195 µm), corpus/isthmus ratio (3.5-5.2 vs 6.2- 10.6), bulb length (14-18 vs 21-28 µm) and diameter (12.0-14.0 vs 14.5-22.0 µm); position of nerve ring (97-103 vs 122-159 µm), excretory pore (103-107 vs 138-167 µm), deirid (115-121 vs 152-180 µm), and phasmid (11-16 vs 23- 32 µm); and length of vagina (10.5-14.5 vs 14.5-17.5 µm) and posterior uterine sac (56-69 vs 80-106 µm). They can furthermore be differentiated by the shape of labial probolae (longer and more slender, bifurcated at over one-half of their total length vs shorter and plumper, bifurcated at about one-third of their total length) and external morphology of cuticle (without continuous longitudinal striation vs with fi ne longitudinal striation).