Phthiracarus tardus Forsslund

Parry, B. W., 1979, A revision of the British species of the genus Phthiracarus Perty 1841 (Cryptostigmata: Euptyctima), Bull. British Mus. nat. Hist., Zool. ser. 35, pp. 323-363 : 350

Phthiracarus tardus Forsslund

(Figs 13D-F; 14; Pl. 5a, d)

Phthiracarus tardus Forsslund , 1956: 216.

Adult (Pl. 5a): Small and weakly sclerotized. The aspis (Fig. 13D) is about 223 µm in length with a greatest width of about 187 µm. All the dorsal setae are fine and short. Setae (il) are about 1-5 times the length of setae (la) and extend two-thirds of the distance il-ro. The rostrals which are inserted relatively far apart do not reach the anterior limit of the aspis. The sensillus (Fig. 13E; Pl. 5d) is 30 - 40 µm in length and broadly clavate. The notogaster (Fig. 13F) is about 497 µm in length with a greatest depth of about 314 µm. All the setae are relatively long (equal to the distance c1 - d1), fine and erect. Setae c1_3 form a row just behind the posterior margin of the collar. Vestigial f1 is located adjacent to seta h1 and towards the mid-dorsal line. The fissures ip and ips are absent. On each anal plate there are only three setae; an1-2 being much longer than ad3. The chelicerae are approximately 147 µm long. The principal segment carries about 16 sharply pointed spines on the paraxial surface and about 9 conical spines antiaxially. The leg chaetotaxy (Fig. 14) is of the 'reduced type' with the setal formulae: I (1-3-2-5-15-1): II (1-3-2-3-12-1); III (2-2-1-2-10-1) and IV (2-1-0-2-9-1). On tarsus I seta u' is short, thick and resembles a eupathidium. Seta ft" on tarsus II is hooked distally and this segment carries a subunguinial seta s.

Distribution: Only a small number of specimens have been recorded in the British Isles from mull soil, Meathop Wood, Westmorland, 19.iii.63 (P. N. Lawrence).

Remarks: P. tardus is somewhat unusual in bearing 12 setae on tarsus II and by having a hooked posterior fastigial seta on this segment (both features are generally associated with 'complete chaetotaxy' species).

A comparison of British and paratype material revealed no morphological differences.