Trhypochthonius silvestris Jacot, 1937

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 : 9-11

Redescription of Trhypochthonius silvestris Jacot, 1937

( Figs. 6 , 4c , 5c )

Trhypochthonius silvestris Jacot, 1937: 353 .

Trhypochthonius silvestris Jacot, 1937 : Seniczak & Norton (1994: adult p. 42).

Diagnosis. Body length about 520–585 µm. Only some notogastral setae distally broadened with spinose setulae (c 2, c 3, e 2, f 2, h 1); setae c 1, d 1 and d 2 thin and very short with few small setulae, (about 10-12 µm); e 1 similar in shape but about 20 µm long; p 1 the longest (about 85 µm), pointed, with setulae; p 2 comparatively long (about 75 µm) pointed; h 3 and p 3 smooth, pointed and short. 9-11 pairs of genital setae (rarely 8). Notogaster with posterior boss.

General characters. Mean body length 554 µm, measured range 524–584 µm; mean length of notogaster 404 µm, mean width 337 µm (n=5; cf. tab. 2).

Prodorsum. Rostral seta about 70 µm long, acuminate, with setulae (seta type 3: cf. Fig. 1a ); lamellar seta about 65 µm, blunt (seta type 4); interlamellar similar, about 100 µm long.

Notogaster. Detailed length values of all setae in table 2; shapes of setae in Fig. 4c . With distinct boss.

Ventral region. As typical for the genus. The genital setation ( Fig. 5c ) is slightly variable within the range of 9-11 pairs, predominant number is 10 (one specimen at one side 8).

Material examined. We studied some specimens donated by Dr. Roy Norton from his collection, which allowed us to compare the American species with European relatives: USA, North Carolina, Durham Co.; Duke Forest. Leg. L. J. Metz 4.5.197 9, from litter of Pinus taeda .

Remarks. The species is smaller than T. tectorum and T. americanus . The lateral notogastral setae (c 3 – f 2) are absolutely and proportionally smaller and less broadened than those of T. tectorum and T. americanus . The best diagnostic characters are the small to very small dorsocentral setae (c 1, d 1, d 2, e 1) in combination with the comparatively long posterior setae (p 2, p 1, h 2). Seniczak & Norton (1994) described the juvenile instars in comparison with those of T. americanus .

Fujikawa (2000) described Trhypochthonius misumaiensis from the Japanese Isle of Hokkaido (near Sapporo) which may be a synonym of T. silvestris , considering the genital setae number (11–12 pairs) and the similar notogastral setation. Differences are the significantly larger body (629-643 µm length) and some larger notogastral setae, e.g. c 3, e 1 and f 2. We do not know the variability of setal lengths (Fujikawa measured only two specimens) nor do we have data on the opisthonotal gland secretion or on the molecular-genetic characters. Therefore, we regard the species provisionally as a subspecies of T. silvestris , as discussed below.

Distribution and ecology. Typical form known only from North America, inhabiting litter of Pinus, Juniperus and also of deciduous trees ( Seniczak & Norton 1994).

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 6. Trhypochthonius silvestris, dorsal view, legs omitted. Scale bar 100 µm.