LIP REGION STRUCTURE IN ACROBELINAE (NEMATODA, CEPHALOBIDAE)

Head structures are described and compared from scanning electron micrographs for 14 spp. [Acrobeles sp., A. capensis, A. singulus, A. chelatus, A. complexus, Stegelleta sp. 1, Stegelleta sp. 2, Zeldia tridentata, Chiloplacus trifurcata, Nothacrobeles lepidus, Pseudacrobeles sp., Acrobeloides sp. 1, Acrobeloides sp. 2 and Acrobeloides sp. 3]. The lip region in Acrobelinae is conical, sometimes significantly elongate quite apart from the impression of elongation conferred by the development of lip appendages, labial and cephalic probolae, characteristic of the subfamily. The level of insertion of the labial probolae on the oral cone structure is close to the top of the cephalic probolae. Although cephalic probolae are flap like, the major part of each probola is directly attached to the oral cone, usually through a radial ridge connecting it to tangential ridges joining the bases of the labial probolae. The disposition of lip region sensilla suggests that the 3 labial probolae and the 6 or 3, cephalic probolae are each outgrowths of the lip sectors. Where appendages are 3 in number, each is formed by fusion from 2 adjacent sectors. In some genera/species the lips are represented by distal lobes, not modified to cephalic probolae.