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 dwarf crocodiles Osteolaemus tetraspis Cope and one slender-snouted crocodile Crocodylus cataphractus Cuvier were dissected for pentastomids. Of the three species recovered, one, found in both hosts, accounted for 66% of the specimens (N = 236) and most of these (N = 150) came from a single host. On the basis of these specimens a new genus, Agema, is described. The type-series consisted of nine adult males and five adult females, together with a complete sequence of instars beginning with the 'double-hooked' infective nymph which gains entry to crocodiles when these consume infected fish intermediate hosts. The evidence suggests that three instars separate the adult female from this infective instar, whereas only two are required in the case of males. Adult males 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 with increasing age. The terminal part of the abdomen of females is abruptly tapered to a bluntly rounded point. Adult hook morphology is identical in both sexes; hooks are smooth with a gently curved barb and they become progressively more chitinised with each ecdysis. The buccal cadre is bridged anteriorly by chitin which appears to be crescentic when viewed from the ventral aspect and another crescent is present towards the pharynx - such a structure most closely resembles that of certain members of the genus Sebekia. The closest counterpart of the Agema 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 which is typical of all members of the family Sebekidae. However, all but one of the succeeding instars have smooth hooks and, uniquely, instar 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 extension in the form of a delicate cowl into which hooks can probably retract. In adult males and pre-adult females (instar IV) and adult females (instar V), this is absent. Small differences in hook size between the anterior and posterior hooks, mostly accounted for by the blade, and apparent in all instars except instar I, are most pronounced in the final instar of both sexes. Smooth, gently curved