Phthiracarus laevigatus (C. L. Koch)

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 : 343-344

Phthiracarus laevigatus (C. L. Koch)

(Fig. 10D-F; Pl. 4e)

Hoplophora laevigata Koch , 1841: Fasc. 38 t.16; 1842: 116.

Phthiracarus laevigatus : Jacot, 1936: 167; van der Hammen, 1963: 704 (neotype designated).

Adult: Large and strongly sclerotized. The aspis (Fig. 10F) ranges in length from 406 - 456 µm with a greatest width of 355 - 400 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 sensillus (Fig. 10E) is about 50 µm long, narrow and finely serrated. The notogaster (Fig. 10D) ranges in length from 812- 1065 µm with a greatest depth of 521 -771 µm, and in lateral view is seen to be sharply angled at the level of seta c1 (Pl. 4e). The latter is inserted relatively far back. All the setae are short (less than the distance c1 - d1), fine and procurved. Vestigial f1 is located midway between setae h1 and ps1. The fissures ip and ips are present. On each anal plate there are only three setae, an1_2 being much longer than ad3. The leg chaetotaxy is of the 'complete type' with the setal formulae: 1(1-4-2-5-16-1); 11(1-3-2-3-12-1); 111(2-2-1-2-10-1) and IV(2-l-l-2-10-l).

Distribution: Three specimens only have been recorded in the British Isles from beech litter, Old Winchester Hill, Hampshire, 1971 (D. R. Kirne).

Remarks: P. laevigatus is quite distinetive, being easily recognized by the marked angle of the notogaster at the level of seta a. The leg chaetotaxy is similar to that noted for the other 'com- plete chaetotaxy' species; on tarsus I the solenidion omega2 is coupled with a small distal seta, a feature not mentioned by van der Hammen in his redescription. The British material has been compared with the neotype from Regensburg - no morphological differences could be detected. P. brevisetae Jacot, described from decaying grass, Monroe, Connecticut, USA, appears to be close to P. laevigatus . The holotype (slide no. 2534h) has been examined and found to be badly damaged. Jacot's description (Jacot, 1930), however, agrees well with van der Hammen's (1963) and with the British material, but the attitude of the notogastral setae appears to differ slightly. In P. laevigatus the notogastral setae are procurved while in P. brevisetae they are directed posteriorly.