All members of the genus Arrhopalites have only one ocellus on each side of the head. Arrhopalites pygmaeus is a common species. Almost all the records are from caves. The empodium of the foot has a long filament that reaches slightly beyond the tip of the claw (Figs. 1, 2). The fourth antennal segment (ant4) is divided into five clearly defined subsegments (Fig. 3). Both the inner and outer edges of the mucro are serrated (Fig. 4) and the female sub-anal appendage is simple (i.e. not expanded at the tip; Fig. 5). In Arrhopalites pygmaeus, the first subsegment of ant4 is about the same length as ant3 (Fig. 3). In Arrhopalites terricolus (for which there is one doubtful Irish record), the first subsegment of ant4 is much shorter than ant3. However, I am not convinced that Arrhopalites terricolus (if it is a good species) could be clearly recognised in UK/Eire material as the length of the first subsegment of ant4 is quite variable in the specimens of Arrhopalites pygmaeus that I have examined.
Fig. 1 (above): Foot of the first leg of Arrhopalites pygmaeus collected from a cave in Eryr, Brecon, Wales in March 1970 (collector unknown).
Fig. 2 (above): Foot of the third leg of the same specimen of Arrhopalites pygmaeus shown in Fig. 1.
Fig. 3 (above): Antenna of Arrhopalites pygmaeus collected from Arne Big Wood, Dorset in November 1963 by Peter Lawrence. The fourth antennal segment (ant4) is clearly divided into five subsegments (1 to 5).
Fig. 4 (above): Distal furca of the same specimen of Arrhopalites pygmaeus shown in Fig. 1. Both the inner and outer edges of the mucro are serrated.
Fig. 5 (above): Female sub-anal appendages (SAA) of the same specimen of Arrhopalites pygmaeus shown in Fig. 1. They are not expanded at the tip.
