Observations On the Cuticle Ultrastructure in the Hoplolaiminae (Nemata: Hoplolaimidae)

Abstract

The fine structure of the cuticle of Aorolaimus macbethi, Aphasmatylenchus straturatus, A. variabilis, Helicotylenchus dihystera, H. multicinctus, Hoplolaimus pararobustus, H. seinhorsti and Pararotylenchus hopperi is described. Six layers are identified in Aphasmatylenchus, Helicotylenchus and Pararotylenchus species vs seven in Hoplolaimus and Aorolaimus species. The ultrastructure of the five outer layers of the cuticle 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 layer; the basal zone of the cuticle consists of a thin electron-lucent layer in Helicotylenchus and Pararotylenchus species and a thick electron-lucent layer representing half of the total thickness of the cuticle in Aphasmatylenchus species; in Hoplolaimus and Aorolaimus species, two layers are present: a thin electron-dense layer consisting of densely packed osmophilic corpuscules and a thick electron-lucent layer. Intracuticular canals previously described in other genera in the subfamily occur in all species studied and may be considered constant in Hoplolaiminae; observations on lateral fields in cross section reveal a variability of their shape and of the deepness of incisures. Three major groups in the subfamily may be distinguished based on ultrastructure and relative thickness of the layers of the cuticle: i) Hoplolaimus, Scutellonema and Aorolaimus, ii) Pararotylenchus and Helicotylenchus, iii) Aphasmatylenchus and Rotylenchus. Cuticle ultrastructure in Hoplolaiminae appears totally different from that observed in other taxonomic groups of the order Tylenchida.