Trhypochthonius japonicus, 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 : 16-18

Trhypochthonius japonicus n. forma occidentalis

( Figs 8 , 4e , 5e , 9b )

Differential diagnosis. Body length about 680–750 µm. Shape of notogastral setae as in nominate form; setae c 1 and c 2 (range 16-21 µm) distinctly shorter than c 3 and d 3 (52-70 µm), d 1 and smaller d 2 (18-26 µm), e 1 of medium length (41-54 µm); posterior notogastral setae longer, p 1 the longest (92-108 µm), spinose and acuminate; p 2 remarkably long (about 82 µm), acuminate and sparsely spinose; h 3 and p 3 smooth setiform (17- 38 µm), less than half the length of p 2. 12–14 pairs of genital setae, mostly 13.

General characters. Mean body length 717 µm, measured range 682–746 µm; mean length of notogaster 507 µm, mean width 417 µm (n=6).

Prodorsum. Sensillus about 85 µm long with slender head; rostral seta about 83 µm long, acuminate, with setulae (seta type 3: cf. Fig. 1a ); lamellar seta about 88 µ m long, bacilliform with setulae (type 4); interlamellar seta about 125 µm long, acuminate, with setulae (type 3).

Notogaster. Detailed length values of all setae in table 3; shapes of setae in Figs 4e and 9b . With distinct posterior boss.

Ventral region. As typical for the genus. The genital setation ( Fig. 5e ) is slightly variable within the range from 12–14 pairs, median number is 13, often asymmetrically expressed.

Material examined.

(1) Austria, Carinthia, Waidischbach near Ferlach; leg. G. Raspotnig, 22.2.200 7 and 24.9.2008; from litter and moss in a Pinus stand. Five specimens .

(2) Austria, Tyrol, Kranebitter Au near Innsbruck; leg. Heinrich Schatz, March 2000; moist litter in a deciduous forest. Four specimens .

(3) Germany, Bärenklau Forest northern Berlin; leg. G. Weigmann, 1991; from litter and moss in a Pinus stand. One specimen.

Remarks. The most obvious difference between the two forms of Trhypochthonius japonicus is in the number of genital setae: 6–10 (median 8) in the Japanese form, 12–14 (median 13) in the European form B (= forma occidentalis). The notogastral setation profile is very similar, but some setae appear a little stronger (cf. the form types indicated in table 3) in forma occidentalis from Austria, compared to those of the nominate form from Shigoku Island, Japan ( Aoki 1970). Except seta h 2 and p -setae, all notogastral setae are consistently longer in forma occidentalis, both absolutely and in relative proportions, yet the differences mostly are not significant (see table 4 in the statistical section below). Also there is a tendency for larger bodies in the European forma occidentalis, though we have few data (n=3 for the Japanese form, n=6 for the European form from Carinthia; the Innsbruck-population has the same range) and ranges overlap (tab. 3). Small differences occur also among populations of Trhypochthonius tectorum from different origins (see the statistical section below). With such limited sampling of the Palaearctic region, we do not overestimate the taxonomical relevance of the differences between the studied populations in Japan and Europe, so we propose only a regional form for the European populations. This proposal is supported by the fact that the profile of the oil gland secretion of the European population is identical to that of the Japanese T. japonicus as described by Sakata et al. (2003) (G. R., unpublished).

Trhypochthonius misumaiensis Fujikawa, 2000 has the same range of genital setation (11–12 pairs) and a similar notogastral setation as does T. japonicus forma occidentalis. Yet the body is smaller (629–643 µm length) and there are some notogastral setae with stronger setulation: c 3, f 2, h 2, p 2. Most notogastral setae are distinctly shorter, especially c 1, c 2, d 1, d 2, which are less than 15 µm. We regard T. misumaiensis to be a subspecies of T. silvestris (see above).

Distribution and ecology. The nominate form of Trhypochthonius japonicus has been found only in Japan (Shigoku Island); the European forma occidentalis has been found only in Austria and northern Germany. In Europe T. japonicus seems to prefer moderately dry to moist litter in forests. The European records in Carinthia and North Germany are syntopic with T. silvestris europaeus n. subsp.

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 8. Trhypochthonius japonicus forma occidentalis, dorsal view, legs omitted. 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.