Deuteraphorura inermis (known as Onychiurus fimetarius or Onychiurus cebennarius in earlier literature) is a common and widespread species However, it appears to be absent from northern Scotland. Deuteraphorura inermis does not possess anal spines or a furca. The post-antennal organ (PAO) is elongate and contains about 12 to 15 complex vesicles (Fig. 1). The first thoracic segment (th1) has 1+1 dorsal pseudocelli (PSO) (Fig. 2). The tibiotarsus of the leg bears only nine distal setae. There is no inner tooth on the claw, and males possess a field of only slightly thickened ventral setae on the third abdominal segment (abd3). The largest specimen I have seen was 2.4 mm in length. The typical PSO formula is 32/133/33354 but their number and arrangement on the body is extremely difficult to determine, especially in permanent slide mounts. In the specimens I have examined, there have been numerous examples of asymmetry and it is clear that the PSO formula (sensu Gisin) needs to be treated with extreme care if it is to be used as a method of separating species. Several of the records are from caves.
Fig. 1 (above): Post-antennal organ (PAO) of Deuteraphorura inermis collected from Kingswood Copper Mine, Devon in April 1969 by W.G. Maxwell. The PAO is of the typical 'Onychiurus' type with complex vesicles.
Fig. 2 (above): Dorsal side of the first thoracic segment (th1) of Deuteraphorura inermis collected from Binfield Park, Berkshire in January 1951 by E. Britton. There is one pseudocellus (*) on either side of the midline.
Fig. 3 (above): Foot of the third leg of the same specimen of Deuteraphorura inermis shown in Fig. 2. The distal part of the tibiotarsus bears nine setae.
Fig. 4 (above): Foot of the third leg of Deuteraphorura inermis collected from Kingswood Copper Mine, Devon in April 1969 by W.G. Maxwell. The empodium (emp) is almost the same length as the claw.
