The Anatomy of the Gnathosoma of Pergamasus vargasi n. sp. (Acarina-Mesostigmata-Gamasides)

Abstract

In the present paper, which is one of a series of studies on the gnathosomai structures of the mesostigmatid acarina, the feding apparatus of the gamasid mite, Pergamasus vargasi is described and figured. About thirty specimens of this mite were collected by H. Rolund in March and July of 1948 from the nests of Microtus sp. in Venango and Warren Counties, Pennsylvania. The specimens were not immersed in a fixilig solution so satisfactory sections of the mites were not possible. The present study is made from whole mounts and from dissections of the gnathosoma. The methods used are the same as described in a recent paper on Megisthanus floridanus (Gorirossi and Wharton, 1953) . B6rner published in 1903 Die Mundbildung bei den Milben. In this magnificent study he attempted to homologize the mouth parts of the Arachnoidea with those of the Acarina. He chose what he considered to be a primitive type, Pergamasus crassipes, to illustrate the similarity between the two groups. The details of this classical piece of work need not be of concern here. The main point of interest for the moment is in the terminology he used for the various gnathosomal parts. B6rner's figure 4 of P. crassipes (fig. L) is included in the present paper in order to compare the gnathosomal structures of P. crassipes with those of P. vargasi. Acknowledgement.-The author wishes to express her thanks to Dr. G. W. Wharton of the University bf Maryland for his helpful advice and criticism. Gnathosoma.-The gnathosomas of the male and female of P. vargasi. are in general essentially similar and yet in some details strikingly different. In the male the hypostomal region is more clearly differentiated from the protosternal region; the hypostomal processes of the male are more pronounced than thosie of the female; and the teeth on the hypopharyngeal processes are more extensive in the male than are those of the female. The chelicerae are the structures which offer the most outstanding differences between the sexes. The gnathosomal ring of both sexes is circular in outline and heavily