Smitella thambetosa, n. gen. and n. sp., a remarkable "helmeted" flea from New Guinea (Siphonaptera, Pygiopsyllidae) with notes on convergent evolution.

Abstract

Smitella thambetosa n. gen. and n. sp., the only known pygiopsyllid flea with a true “helmet” or a vertical head comb, is described and figured. However, the comb in the helmet is composed of highly modified bristles and cannot be considered homologous with that of other helmet-fleas (Stephanocircidae and Macropsyllidae) despite similarities in appearance. Other remarkable parallelisms in the development of the pygiopsyllid helmet include separation from the rest of the head; presence of a large canal and many submarginal canaliculi, bordered by narrow sclerotized lines; displacement of the preantennal sensory placoids, etc. Examples are cited and illustrated of other modifications of the head of pygiopsyllid and other fleas, such as development of rows or masses of spiniform bristles, vertical combs and flattening of the frontal margin, all of which seem adaptive and aid the flea in remaining secure among the hairs of its host. The presence of structures of this type is apparently correlated with possession of unusually broad forecoxae. “False combs” of fleas are discussed, and it is shown that they only occur on those parts of the body which do not bear the usual ctenidium of true spines in the respective related taxa. It is pointed out that peramelid fleas characteristically have pronotal spines which are highly acuminate, i.e. stiletto-shaped.