Phthiracarus membranifer, Parry, B. W., 1979

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 : 344-346

Phthiracarus membranifer sp. nov.

(Fig. 11A-C)

Adult: Small and weakly sclerotized. The aspis (Fig. 11C) ranges in length from 213 - 324 µm with a greatest width of 157 - 243 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 latter do not reach the anterior limit of the aspis. The sensillus (Fig. 11B) is 70 µm long, narrow, membranous marginally and reminiscent of that of P. juvenalis . The tracheoles are short and finger-like. The notogaster (Fig. 11A) ranges in length from 314 - 517 µm with a greatest depth of 223 - 324 µm. All the setae are relatively long (equal to the distance c1 - d1), fine and almost erect. Setae c1 and c3 are situated on the posterior margin of the collar and just anterior to seta c2. Vestigial f1 is located a short distance posterior to seta h1. The fissures ip and ips are absent. On each anal plate there are only three setae; an1-2 being much longer than adj,. The chelicerae are 116- 167 µm long. The principal segment carries 9-23 sharply pointed spines on the paraxial surface and 8-20 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 (2-1-0-2-9-1). On tarsus I seta u is short, thick and resembles a eupathidium. In one paratype the 'complete chaetotaxy' condition of tarsi I to IV (16, 12, 10 and 10) is associated with a 'reduced chaetotaxy' condition on femur I (3) and genu IV (0).

Types: Holotype, BMNH reg. no. 1976.2.18.14, and two paratypes, 1976.2.18.15-16, from Sitka spruce F, Tintern Forest, Monmouthshire, 4.vi.73 (B. W. Parry).

Distribution: P. membranifer was also recorded from Higher Kiln Quarry, Devon, 25.iv.64 (C. Moreby) and from Torboll, Sutherland, 29.vi.76 (P. D. Hillyard). This species was not abundant in any of the samples examined.

Remarks: The smallest of the British species examined, P. membranifer is somewhat unusual in bearing vestigial f1 posterior to the seta h1 (a feature generally associated with the larger 'complete chaetotaxy' species).