The morphology of the palp in two families of ticks (Acarida: Ixodina). A contribution to the study of the Anactinotrichida 1)

The mite order Anactinotrichida consists of three distinctly related suborders, viz., Holothyrina, Ixodina, and Gamasina2). Recently, in a morphological study of a species of Holothyrus (Van der Hammen, 1961), I published a short list of ordinal characters, in which I mentioned that the tarsus of the palp is relatively small. At first sight this character does not hold good for the tick family Argasidae, where the terminal palpal segment is of normal length. It must be noted, however, that the palp of the ticks consists of four segments only (one of these being apparently a fusion of two), so that they are generally referred to by the numbers 1 to 4. In the course of a morphological investigation of the Ixodina according to the method used for my Holothyrus paper, I studied the palp of two species of ticks, viz., Ornithodoros (Ornithodoros) savignyi (Audouin) and Hyalomma dromedarii C. L. Koch, respectively belonging to the Argasidae and to the Ixodidae (the two main tick families) 3). The present paper contains the result of this comparative study; the two palps are described and figured, and an attempt is made to draw preliminary conclusions on the homology of the segments. Complete data on the material are given with each species. DESCRIPTION OF THE PALP OF A SPECIES OF THE FAMILY ARGASIDAE (fig. 1) Ornithodoros (Ornithodoros) savignyi is dealt with here as an example of the Argasidae. The material investigated for this study consists of numerous specimens from a sheep resting place, Mansuriya, Imbaba, Giza Fig. 1. Ornithodoros (Ornithodoros) savignyi (Audouin), right palp of the female. A,