Phthiracarus juvenalis, 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 : 342-343

Phthiracarus juvenalis sp. nov.

(Fig. 10A-C; Pl. 4b, d)

Adult (Pl. 4b): Medium-sized and weakly sclerotized. The aspis (Fig. 10C) ranges in length from 258 -279 µm with a greatest width of 213 -223 µm. All the dorsal setae are moderately long and fine. Setae (il) are about 1-5 times the length of setae (la) and equal to the distance il-ro. The latter do not reach the anterior margin of the aspis. The sensillus (Fig. 10B; PL 4d) is rather long (80 µm), narrow and pointed distally. The tracheoles are short and finger-like. The notogaster (Fig. 10A) ranges in length from 558 - 588 µm with a greatest depth of 365 - 406 µm. All the setae are short (less than the distance c1 - d1), fine and directed posteriorly. Setae c1 and c3, are inserted close to the posterior margin of the collar and seta c2 submarginally. Vestigial f1 is located a short distance posterior to seta h1. The fissures ip and ips are absent. On each analplate there are two setae in the anal series and one in the adanal series; all are moderately long and more or less equal in length. The chelicerae are approximately 152 µm long. The principal segment carries about 19 sharply pointed spines on the paraxial surface and about 15 conical spines antiaxially. The leg chaetotaxy is of the 'complete type' with the setal formulae: I (1-4-2-5-16-1); II (1-3-2-3-12-1); III (2-2-1-2-10-1) and IV (2-1-1-2-10-1).

Types: Holotype, BMNH reg. no. 1976.2.18.6, and one paratype, 1976.2.18.7, from leaf litter, Higher Kiln Quarry, Buckfastleigh, Devon, 25.iv.64 (C. Moreby).

Distribution: Common in mor forest soils. P. juvenalis was recorded under both the hard- wood and coniferous tree species at each of the study areas(see p. 324)being particularly abundant in beech and oak F where it accounted for 5-15% of the euptyctimoid population. Other material was examined from Woodwalton Fen, Huntingdonshire, 20.V.65 (P. N. Lawrence) and from Castor Hanglands, Northamptonshire, 21.vi.63 (P. N. Lawrence).

Remarks: Of the species examined with a 'complete chaetotaxy', P. juvenalis is the only one to possess a rather long sensillus and backwardly directed notogastral setae.

P. ligneus , recorded by Willmann (1932) in humus, moist Juncus and moss on the Dummersdorf bank, River Trave, West Germany, shows an overall similarity to P. juvenalis . The syntype series (five specimens mounted in Canada Balsam) has been examined, and in comparison to P. juvenalis the specimens found to be much smaller (notogastral length 375 - 420 µm) while the notogastral setae and the sensilli are distinctly longer than in P. juvenalis .

P. juvenalis also resembles two recently described species, P. clemens Aoki 1963 from Tokyo and P. crispus Hammer 1972 from Tahiti. However, in comparison with P. juvenalis , topotypes of P. clemens were found to be larger (notogastral length about 700 µm) while the holotype of P. crispus was much smaller (notogastral length about 430 µm). Moreover, in contrast to P. juvenalis , the notogastral setae of both species are procurved.