natural, history

Issued IS. December 1958.26. MALLOPHAGA (INSECTA). PART IIA NEW SPECIES O~ IBIDOECUS CUM MINGS, 1916BYB. K. T ANDAN, M. Sc., Ph. D.DEPARTMENT OF ZOOLOGY, LUCKNOW UNIVERSITY, INDIAIbidoecus dianae sp. n.(Text-figs. 1-6)Type host: Threskiornis molucca pygmaeus MayrA critical examination of the characters shows that this species is intermediatebetween I. clausus (Giebel) from Threskiornis melanocephala (Latham) and a newspecies from Pseudibis papillosa (Temminck). This latter species, the description ofwhich is now in the press, is referred to throughout this paper as lbidoecus newspecies.The characters to be taken into consideration in comparing males of relatedspecies are the genitalia and the sternal thickening on segment V]1. ]n the formercharacter dianae shows a greater degree of resemblance to clausus than to eitherthreskiornis or the new species, in the nature of the sternal thickening on segment VIIit resembles both clausus and threskiornis. This thickening in the species examinedfrom ibises belonging to the genus Threskiornis is in the form of a median platewhereas in the new species from Pseudibis papillosa (Temminck) it is in the form oflateral plates. The three mesosomal sclerites are basically identical in shape inclausus and dianae, differing only in their size and proportions; the parameres andthe median sclerite (fig. 2, m) also exhibit similar differences. ]n the mesosome, theventral-most sclerite in threskiornis and the penis in lhidoecus new species are markedlydifferent and these characters, along with differences in the abdominal chaetotaxy,the size of the parameres and the size and shape of the median sclerite. readily separatethese forms from the two former species. From clausus it can be distinguished bythe dorsal abdominal chaetotaxy and the genitalia, especially by the shape and proportionsof the mesosomal sclerites.The female, on the contrary, unequivocally resembles lbidoecus new species inpossessing a median, butterfly-shaped, post-vulval sclerite with oblique thickeningand another adjacent sclerite each side, and in the position and length of the tergocentralsetae on the terminal abdominal segments (lX-X]); these setae are not placed. on the tergal plates and normally extend beyond the posterior margin of the abdomen.In threskiornis and clausus the post-vulval sclerites are of altogether differentshapes; the tergocentral setae in threskiornis are not only placed on the tergites butfall considerably short of their posterior margin, while in clausus these setae are151