OBSERVATIONS ON THE CUTICLE ULTRASTRUCTURE IN THE HOPLOLAIMINAE (NEMATA, HOPLOLAIMIDAE)

The fine structure of the cuticle of Aorolaimus macbethi, Aphasmatylen chus straturatus, A. variabilis, Helicotylenchus dihystera, H. multici nctus, Hoplolaimus pararobustus, H. seinhorsti and Pararotylenchus hop peri is described. Six layers are identified in Aphasmaylenchus, Helic otylenchus and Pararotylenchus species vs seven in Hoplolaimus and Aor olaimus species. The ultrastructure of the five outer layers of the cu ticle is identical in all species and consists of an external cortex, an internal cortex, a granular or fibrillar layer with electron dense ovoid structures, a striated layer and an electron dense fibrillar lay er; the basal zone of the cuticle consists of a thin electron-lucent l ayer in Helicotylenchus and Pararotylenchus species and a thick electr on-lucent layer representing half of the total thickness of the cuticl e in Aphasmatylenchus species; in Hoplolaimus and Aorolaimus species, two layers are present: a thin electron-dense layer consisting of dens ely packed osmophilic corpuscules and a thick electron-lucent layer. I ntracuticular canals previously described in other genera in the subfa mily occur in all species studied and may be considered constant in Ho plolaiminae; observations on lateral fields in cross section reveal a variability of their shape and of the deepness of incisures. Three maj or groups in the subfamily may be distinguished based on ultrastructur e and relative thickness of the layers of the cuticle: i) Hoplolaimus, Scutellonema and Aorolaimus, ii) Pararotylenchus and Helicoylenchus, iii) Aphasmatylenchus and Rotylenchus. Cuticle ultrastructure in Hoplo laiminae appears totally different from that observed in other taxonom ic groups of the order Tylenchida.