Phthiracarus clavatus, 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: 338-339

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Phthiracarus clavatus

sp. nov.

Phthiracarus clavatus  sp. nov.

(Fig. 7A-C; Pl. 3c, f)

Adult (Pl. 3c): Large and strongly sclerotized. The aspis (Fig. 7C) ranges in length from 279 - 324 µm with a greatest width of 192 - 208 µm. All the dorsal setae are long and conspicuous. Setae (it) and (la) are more or less equal in length and both pairs of setae reach the level of the rostrals. The latter extend to the anterior margin of the aspis. In the paratype setae (la) are only half the length of setae (it). The sensillus (Fig. 7B; PI. 3f) is 30 - 40 µm long, broadly clavate and distinctly serrated in the distal half. The notogaster (Fig. 7A) ranges in length from 619 - 659 µm with a greatest depth of 421 - 458 µm. All the setae are long (more than the distance c1 - d1) and procurved. Setae c1_3 form a row just behind the posterior margin of the collar. Vestigial f1 is located a short distance posterior to seta h1. The fissures ip and ips are absent. On each anal plate there are five long setae; an1-2 and ad3 being more or less equal in length and somewhat shorter than ad1-2. The chelicerae are approximately 182 µm in length. The principal Segment carries about 20 sharply pointed spines on the paraxial surface and about 18 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). On tarsus I the distal seta coupled with solenidion omega2 is rather short. Seta d on femur I is long, straight and only weakly serrated.

Types: Holotype, BMNH reg. no. 1976.2.18.1, from mull soil, Meathop Wood, Westmorland, 19.iii.63 (P. N. Lawrence). Paratype, 1976.2.18.2, from Phragmites  litter, Woodbastwick Marshes, Norfolk, 10.vii.74 (S. J. Moore).

Distribution: P. clavatus  was also recorded from The Woburn Estate, Bedfordshire, 10.iv.72 (B. W. Parry) and from Rosthwaite, Cumberland, 18.V.59 (P. N. Lawrence). This species was not abundant in any of the samples examined.

Remarks: P. clavatus  appears to be similar to P. borealis ( Traegaerdh)  recorded in rotting birch leaves, Sarek, Swedish Lapland. Three 'cotypes' of borealis  (cleared but undissected) were ex- amined and found to be generally larger (notogastral length 659 - 842 µm) and more heavily sclerotized than clavatus  . Moreover, in P. borealis  the notogastral setae are erect while in P. clavatus  they are procurved. The general form of the sensillus is similar in both species.

P. clavatus  also resembles P. setosellum bryobium  described by Jacot (1930) from upland swamp moss, East Village, Monroe, Connecticut, USA. However, in comparison with clavatus  , the 'cotype' of setosellum bryobium is much smaller (notogastral length about 252 µm). The notogastral setae appear to be of the same general form in both species. The sensillus, which appears to be lobular in Jacot's figure, is missing in the 'cotype'.