Ultrastructural variation of cuticular layers in Cephalobinae (Nemata : Rhabditida)

The ultrastructure of the body wall cuticle in Acrobeles complexus, Cervide llus alutus, and Zeldia punctata was studied as a step toward understanding biological diversity within Cephalobinae, and to discover new characters f or phylogeny-based classification of the suborder. In each species the cuti cle consists of cortical, median, and basal layers. The cortical layer incl udes an external trilaminate and internal granular zone; the basal layer is striated. In Z. punctata the median layer is electron-lucent, vacuolar, an d penetrates the cortical layer; it also includes periodically dense column s that apparently correspond to punctuations visible with light microscopy. In contrast, the median layer of the body wail cuticle in A. complexus and C. alutus is bisected by a zone that undulates parallel to the nematode su rface and with periodicity corresponding to annuli. Phylogenetic analysis, using derived cuticle patterns of Cephalobinae, requires an understanding o f ecological pressures that could result in convergent evolution of cuticle characters.