Trhypochthonius silvestris europaeus, Weigmann & Raspotnig, 2009

Weigmann, Gerd & Raspotnig, Günther, 2009, Comparative morphological and biometrical studies on Trhypochthonius species of the tectorum species group (Acari: Oribatida: Trhypochthoniidae), Zootaxa 2269 (1), pp. 1-31 : 12-15

Description of Trhypochthonius silvestris europaeus n. subsp.

( Figs 7 , 4d , 5d , 9c–e )

This European taxon is closely related to the American Trhypochthonius silvestris , which is substantiated by the statistical analysis below. The main differences are as follows.

Differential diagnosis. Body length about 540–620 µm. Most notogastral setae distally broadened with spinose setulae (all c- and d- setae, e 2, f 2, h 1, h 2); setae c 1, c 3, d 1 and e 1 distinctly larger than in T. silvestris , p 1 and h 2 smaller. 6–8 pairs of genital setae (mostly 8).

General characters. Mean body length 597 µm, measured range 558–620 µm (a specimen from Sweden with 540 µm length); mean length of notogaster 414 µm, mean width 347 µm (n=12; cf. tab. 2).

Prodorsum. Rostral seta about 70 µm long, acuminate, with setulae (seta type 3: cf. Fig. 1a ); lamellar seta about 75 µm distally broadened; interlamellar seta about 95 µm, bacilliform with setulae (type 4).

Notogaster. Detailed length values of all setae in table 2; shapes of setae in Fig. 4d and 9c,d . With distinct posterior boss ( Fig. 7 , 9d ).

Ventral region. As typical for the genus. The genital setation ( Fig. 5d ) varies from 6–8 pairs, predominant number is 7 (one specimen unilaterally with 8).

Material examined.

(1) Austria, Carinthia, Waidischbach near Ferlach, leg. G. Raspotnig , 22.2.200 7 and 24.8.2008; from litter and moss in a Pinus stand. Twelve specimens. The holotype (Inv.No 07/37865) and two paratypes are deposited in the Senckenberg Museum für Naturkunde, Görlitz , Germany.

(2) Germany, Bärenklau Forest , northern Berlin. Leg. G. Weigmann, 1991; from litter and moss in a Pinus stand. Four specimens .

(3) South Sweden, Öland. Leg. Franz Horak, 20.7.198 7. Two specimens.

Remarks. Considering morphological characters, this taxon is most closely related to typical American populations of T. silvestris . Nevertheless, there are some significant differences in morphometric data, as analysed in the statistical section below. The occurrence of populations in three European countries gives reason for proposing a new European subspecies having a distribution disjunct from the nominate Nearctic subspecies, T. silvestris silvestris .

Balogh (1972: pl. 8, Fig 13 ) figured a specimen of “ Trhypochthonius tectorum ” which is obviously misidentified: The short seta c 2, the very short setae c 1, d 1 and d 2, the moderately long lateral setae (c 3 to f 2) and the dorsal seta h 1 fit best to the description of T. silvestris europaeus n. subsp. This setation differs distinctly from the other two European species T. tectorum and T. japonicus forma occidentalis (described in the next section). In Gilyarov & Krivolutsky (1975: Fig.140) and in Balogh & Mahunka (1983: Fig. 118E) the figures of “ Trhypochthonius tectorum ” are redrawn from Balogh (1972), and therefore also probably represent T. silvestris europaeus n. subsp.

Fujikawa (1995) described Trhypochthonius septentrionalis from the North Japanese Isle of Hokkaido and this may be a senior synonym of T. silvestris europaeus n. subsp. because of the 7 pairs of genital setae, the very similar notogastral setation, and the similar body size (586–636 µm length). We do not know details and variability of the setal lengths (Fujikawa gave no specific measures) nor do we have data on the opisthonotal gland secretion or the molecular-genetic characters. Therefore, we regard the species provisionally as a distinct Japanese subspecies of T. silvestris , as discussed below.

Distribution and ecology. Trhypochthonius silvestris europaeus n. subsp. was found in Austria, Germany and Sweden from moderately dry moss and litter in forests. The European records in Carinthia and North Germany are syntopic with T. japonicus forma occidentalis.

Figures

FIGURE 1. a—Shape types of notogastral setae in the Trhypochthonius tectorum species-group; b—Length measures of notogaster (L NG) and of prodorsum (L PD) on a shrunken specimen; c—the same on a swollen specimen.

FIGURE 4. Profiles of all notogastral setae. a—Trhypochthonius tectorum; b—T. americanus; c—T. silvestris; d—T. silvestris europaeus subsp. nov.; e—T. japonicus forma occidentalis.

FIGURE 5. Genital plates. a—Trhypochthonius tectorum; b—T. americanus; c—T. silvestris; d—T. silvestris europaeus subsp. nov.; e—T. japonicus forma occidentalis. Scale bar 100 µm.

FIGURE 7. Trhypochthonius silvestris, europaeus subsp. nov. a—Sensillus; b—dorsal view, legs omitted; c—Ventral view; d—lateral view. Scale bar 100 µm.

FIGURE 9. SEM pictures. a—Trhypochthonius tectorum, dorsal view; b—Trhypochthonius japonicus forma occidentalis, dorsal view.—T. silvestris europaeus subsp. nov. c – Opisthonotal gland opening and seta f2 in dorsolateral view; d—Dorsal view; e—ventral view with anogenital region.

FIGURE 13. Ranges of length-values of notogaster setae (a, c) and individual length-values plotted against notogaster lengths (b, d) of Trhypochthonius species. a, b—c1 setae; c, d—c2 setae. Abbreviations of species at plots: see fig. 12.