A DESCRIPTION OF AGEMA, A NEW MONOTYPIC PENTASTOMID GENUS FROM THE LUNGS OF THE AFRICAN DWARF AND SLENDER-SNOUTED CROCODILES

The lungs of wild-caught and market-derived crocodiles, including 15 d warf crocodiles Osteolaemus tetraspis Cope and one slender-snouted cro codile Crocodylus cataphractus Cuvier were dissected for pentastomids. Of the three species recovered, one, found in both hosts, accounted f or 66% of the specimens (N = 236) and most of these (N = 150) came fro m a single host. On the basis of these specimens a new genus, Agema, i s described. The type-series consisted of nine adult males and five ad ult females, together with a complete sequence of instars beginning wi th the 'double-hooked' infective nymph which gains entry to crocodiles when these consume infected fish intermediate hosts. The evidence sug gests that three instars separate the adult female from this infective instar, whereas only two are required in the case of males. Adult mal es are claviform and females are banana-shaped; in both sexes the tiny trapezoid head is strongly united with the abdomen. Males possess 52- 58 abdominal annuli, females 58-63, and this number does not change wi th increasing age. The terminal part of the abdomen of females is abru ptly tapered to a bluntly rounded point. Adult hook morphology is iden tical in both sexes; hooks are smooth with a gently curved barb and th ey become progressively more chitinised with each ecdysis. The buccal cadre is bridged anteriorly by chitin which appears to be crescentic w hen viewed from the ventral aspect and another crescent is present tow ards the pharynx - such a structure most closely resembles that of cer tain members of the genus Sebekia. The closest counterpart of the Agem a male copulatory spicule is also found within this genus, but the two genera have very different hook morphologies. Infective Agema nymphs (= instar I) have large, strongly recurved hooks overlain by a spike w hich is typical of all members of the family Sebekidae. However, all b ut one of the succeeding instars have smooth hooks and, uniquely, inst ar III has a patch of minute spines at the base of the hook blade. The fulcrum of both instars II and III is provided with an anterior exten sion in the form of a delicate cowl into which hooks can probably retr act. In adult males and pre-adult females (instar IV) and adult female s (instar V), this is absent. Small differences in hook size between t he anterior and posterior hooks, mostly accounted for by the blade, an d apparent in all instars except instar I, are most pronounced in the final instar of both sexes. Smooth, gently curved hooks, and a singula r permutation of characteristics (notably mouth morphology, body shape and the form of the copulatory spicule), which are important in the g eneric diagnosis of three other genera within the family Sebekiidae (A lofia, Sebekia and Selfia), define this new genus.