Onychiurus ambulans is a common and widespread species found in soil, leaf litter and caves. The largest specimen I have seen was 2.9 mm in length. The furca is absent and there are two anal spines (Fig. 1) with occasional mutations (Fig. 2). The post-antennal organ has from 11 to 13 complex vesicles. The empodium of the foot is long and filamentous and is about the same length as the claw (Fig. 3). The first thoracic segment has 1+1 dorsal pseudocelli (PSO) (Fig. 4). The typical PSO formula is 32/133/33353. Males (Fig. 5) are easy to identify as they have characteristic groups of specialised setae on the ventral side of abdominal segments 2 and 3 (Fig. 6).
     I have examined more than 200 specimens of Onychiurus ambulans in the NHML collection, including two donated by Sir John Lubbock in the 19th century (collected from Uppsala, Sweden). There is some disagreement concerning what we should call this species (in some publications it is called Onychiurus circulans). For the present I have decided to follow the decision of Pomorski (1998) and call it Onychiurus ambulans. Onychiurus laminatipes Bagnall 1937 is a junior synonym of Onychiurus ambulans.
    Specimens of Onychiurus 'rectospinatus' and Onychiurus 'subambulans' collected by Bagnall do not correspond to modern descriptions of these species and they should not be included as definite members of the UK and Eire checklist.

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Fig. 2 (above): Abnormal anal spines (*)of Onychiurus ambulans collected from Bolton in May 1979 by Brian Pitkin. In addition to the normal spines (1, 2), there are two small additional spines (*) adjacent to spine 1.

Fig. 1 (above): Anal spines (*) of Onychiurus ambulans collected from Bolton in May 1979 by Brian Pitkin.

Fig. 3 (above): Foot of third leg of Onychiurus ambulans collected from Bolton in May 1979 by Brian Pitkin.

Fig. 4 (above): Dorsal side of first thoracic segment (th1) of Onychiurus ambulans collected from Bolton in May 1979 by Brian Pitkin.

Fig. 5 (above): Male genital plate of Onychiurus ambulans collected from Bolton in May 1979 by Brian Pitkin.

Fig. 6 (above): Ventral side of second (abd2) and third (abd3) abdominal segments of a male specimen of Onychiurus ambulans collected from Bolton in May 1979 by Brian Pitkin. There are two enlarged setae (S) on abd2 and a setal 'bundle' (sb) of short, stiff setae  on abd3.