Phthiracarus anonymum Grandjean

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 : 336-338

Phthiracarus anonymum Grandjean

(Fig. 6; Pl. 3b, e)

Phthiracarus anonymum Grandjean 1933: 312 (ano-genital region); 1934: 51 (aspis & notogaster); 1950: 73 (setae f1, f2 and ps4); van der Hammen, 1965: 376 (leg chaetotaxy).

[ Phthiracarus anonymum : Felder & Suciu, 1957: 24. Misidentification.]

Adult (Pl. 3b): Small, weakly sclerotized and opalescent. The aspis (Fig. 6C) ranges in length from 208 - 248 µm with a greatest width of 162 - 172 µm. All the dorsal setae are fine and short. Setae (il) are about 1-5 times the length of setae (Ja) and extend two-thirds of the distance il-ro. The rostrals which are inserted relatively far apart are widely removed from the anterior margin. The sensillus (Fig. 6D) is short (20 µm), ovate and serrated. The notogaster (Fig. 6E) ranges in length from 406 - 466 µm with a greatest depth of 253 - 294 µm. All the setae are short (less than the distance c1 - d1), fine and erect. Setae c1 and c3 are inserted on the posterior margin of the collar and seta c2 submarginally. Vestigial f1 is located just dorsal to seta h1. The fissures ip and ips are absent. On each anal plate (PL 3e) there are five relatively short setae, of which, three, evidently ad3 and an1-2, are inserted on the paraxial margin, the longest in the row being am which is approximately twice as long as ad3. The chelicerae are approximately 137 µm in length. The principal segment carries about 12 sharply pointed spines on the paraxial surface and about 10 conical spines antiaxially. The leg chaetotaxy is of the 'reduced type' with the setal formulae: I (1-3-2-5-15-1); II (1-3-2-3-11-1); III (2-2-1-2-10-1) and IV (2-1-0-2-8-1). On tarsus I (Fig. 6A) true setae and eupathidia are difficult to distinguish since the former are more or less straight distally. The distal seta coupled with solenidion omega2 resembles that of P. affinis . Seta u on tarsi I and II is often short and thick and resembles a eupathidium. On tarsus IV (Fig. 6B) seta pv' is absent.

Distribution: P. anonymum , the only endophagous species identified in the present study, is apparently widely distributed in the F layer or mor forest soils. This species was common under both the hardwood and coniferous tree species at each of the study areas (see p. 324) being particularly abundant under oak where it constituted 5 - 10% of the euptyctimoid population.

Material was also examined from: Wytham Woods Estate, Berkshire, 28.x.70 (T. G. Wood); Burnham Beeches, Buckinghamshire, 1964 (G. O. Evans); Bramshill Forest, Hampshire, 6.xii.70 (B. W. Parry); Woodwalton Fen, Huntingdonshire, 20.iv.65 (P. N. Lawrence); Hollows Wood, Kent, 3.iv.60 (P. N. Lawrence); Grasmere, Westmorland, 3.xii.54 (M. Bacchus); Meathop Wood, Westmorland, 19.iii.63 (P. N. Lawrence); Shawley Woods, Worcestershire, 4.X.63 (F. Flowers); Springwell Forest, Co. Londonderry, 1973 (J. Longworth); Perigueux, Dordogne, France (topotypes).

Remarks: In comparison with the other British Phthiracarus species examined, P. anonymum is somewhat atypical: it alone is opalescent; bears f1 dorsal to h1; carries ad3, on the paraxial margin of the anal plate and lacks the anterior primiventral seta on tarsus IV. The British material has been compared with a number of topotypes - no morphological differences could be detected. P. anonymus amicus Jacot , described from deciduous leaf mould, Connecticut Hill, New York, USA, may well prove to be conspecific with P. anonymum . Jacot (1938) based his description on the position of seta d2 and the length of seta an1; d2 was located further towards d1 than was in fact shown in Grandjean's figure (Grandjean, 1934) while seta an1 appeared to be longer. Although Grandjean's figure does indeed differ in these two respects from Jacot's anonymus amicus , the topotypic material of anonymum which has been examined agrees well with Jacot's description. A 'cotype' of anonymus amicus (slide no. 32108h2, undissected and mounted in Canada Balsam) has been examined and appears to be close to anonymum although the seta an1 is difficult to discern. Moreover, Jacot's species (diagonal length of notogaster about 400 µm) falls within the size range given by Grandjean (notogastral length 330 - 420 µm).