Cryptopygus thermophilus (Fig. 1) is moderately common and appears to be confined to Ireland, Wales and southern England. It is greyish in colour, reaches a maximum length of 1.0 mm, and possesses an oval post-antennal organ with eight ocelli on each side of the head. The fifth (abd5) and sixth (abd6) abdominal segments are fused. The furca is longer than the head (Fig. 1) and the mucro has two teeth (Fig. 2). The dorsal side of abd5/6 has several long setae which bear a fringe of tiny 'hairs' about halfway along their length (Fig. 3). Potapov has christened these 'foil setae' (in relation to fencing swords).
Despite the sparse map, Peter Shaw's experience is that this species is common on bare 'brownfield' ex-industrial sites, with especially high densities on pulverised fuel ash sites in southern England. Another recent record is from bare ground near the M25 in Kent. The specific name 'thermophilus' means 'heat loving' - a name that seems to describe its ecology.