Numerous species within the Protaphorura armata 'group' have been described. All have simple vesicles in the post-antennal organ (Fig. 1), a furca present as a tiny vestigial flap, two anal spines, and empodium of the foot long and filamentous about the same length as the claw. The 'typical' PSO formula of Protaphorura aurantiaca is 33/022/33343 but there is considerable variation (Figs. 2 to 5). Brian Pitkin suggested that the number of PSO on the third thoracic segment (th3) could be used for separating Protaphorura aurantiaca (th3 with 2+2 PSO; Fig. 2) and Protaphorura armata (th3 with 3+3 PSO). The red dots on the map show the localities of specimens with 2+2 pseudocelli (PSO) on the third thoracic segment (th3) that I have checked (many were labelled armata). The green dots are literature records for Protaphorura aurantiaca and its synonyms. As can be seen, there is considerable overlap with the distribution of armata (armata and aurantiaca are occasionally found together in the same sample) and the possibility cannot be excluded that they are varieties of the same species. Protaphorura aurantiaca is yellow in life (fades to white in alcohol!) whereas Protaphorura armata is normally white . Other characters (particularly presence or absence of seta s' on abd5, and the degree of convergence of lines drawn through the two pairs of setae anterior to the anal spines) are not reliable in the specimens I have examined. Occasionally, an asymmetrical arrangement of pseudocelli makes it difficult to assign a definitive species identification and it is probably safest to assign such specimens to the Protaphorura armata 'group'.
Fig. 1 (above): Post-antennal organ (PAO) of Protaphorura aurantiaca collected from Bolton in May 1978 by Brian Pitkin.
Fig. 2 (above): Dorsal right side of the third thoracic segment of Protaphorura aurantiaca collected from Harle Syke, Lancs. in March 1934 by H. Britten. There are only two pseudocelli on each side (R1, R2 visible on right side, only L1 visible on the left - L2 is present but is outside the field of view).
Fig. 3 (above): Rear margin of the dorsal side of the fifth abdominal segment (abd5) of Protaphorura aurantiaca collected from Bolton in June 1978 by Brian Pitkin. Note the asymmetrical number of pseudocelli (three on the left, four on the right).
Fig. 4 (above): Rear margin of the right side of the dorsal side of the head of Protaphorura aurantiaca collected from Inchiquin Loch, Clare, Ireland in July 1960 by Bill Hale. Note that there are five pseudocelli (PSO) present (according to the 'classic' description of Protaphorura aurantiaca, there should only be three PSO in this position
Fig. 5 (above): Dorsal side of the first thoracic segment (th1) of Protaphorura aurantiaca collected from Rivington, Bolton in October 1978 by Brian Pitkin. There is a single pseudocellus (PSO) present on the left side (white arrow; according to the 'classic' description of Protaphorura aurantiaca, there should be no PSO on th1).
