Thoracophoracarus silvarum, Gerecke, 2009

Gerecke, Reinhard, 2009, Revisional studies on Thoracophoracarus K. Viets, 1914 (Arachnida, Acari, Hydrachnidia, Arrenuridae), Zoosystema 31 (1), pp. 127-145 : 141

Thoracophoracarus (s.s.) silvarum n. sp. ( Fig. 9 )

TYPE MATERIAL. — Holotype: Madagascar, MD 027, Ionilahy (Fianarantsoa), small stream crossing the railroad E from the village, 200 m, 15.VIII.2001, 19.9°C, 0.083 mS/cm, ♂ ( MNHN Ac1122).

Paratypes: Same site as holotype, 1 ♂ slide-mounted ( MNHN Ac1127). — MD 029, Ionilahy (Fianarantsoa), riv. Avatamboka c. 1 km NW from the village, 210 m, 15.VIII.2001, 21.2°C, 0.077 mS/cm, 1 ♂ in liquid ( MNHN Ac1123). — MD 035, Ranomena (Fianarantsoa), stream NW from the 1.07 km-railway-tunnel (right affluent of MD 034), 19.VIII.2001, 14.8°C, 0.029 mS/cm, 1 ♂ in liquid (coll. Gerecke, Tübingen). — MD 038, Andrambovato (Fianarantsoa), stream 3 km E from the village upstream from the cascade, 900 m, 20.VIII.2001, 1 ♂ in liquid (coll. Gerecke, Tübingen).

ETYMOLOGY. — From the Latin silva, meaning forest.This species appears restricted to a belt of primary and secondary rain-forest on the eastern coast of Madagascar.

DESCRIPTION

Male ( Fig. 9 , female unknown): gnathosomal bay broadly U-shaped. Acetabular fields wider than long, with straight anterior and posterior margins, laterally rounded, bearing about 60 acetabula each. P-2 with 5 or 6 mediodistal setae, P-4 L/H 1.5, maximum H distally. Male gonopore flanked by a pair of flat, rounded extensions (in some specimens a little more prominent than given in Figure 8A ). Measurements: idiosoma L/W 600-700/470-560, W Cx-4-tips 590-580); acetabular field L/W 76- 80/280-320; palp (L/H): P-1 30/28, P-2 92/69, P-3 60/60, P-4 92/62, P-5 50/16. Legs (L/H): IV-L-4 135/42, IV-L-5 135/38. Swimming setae numbers (anterior/posterior): IV-L-4 4/5, IV-L-5 0/5.

REMARKS

In comparison with the other species of the group, T.silvarum n. sp. is characteristic in the combination of a U-shaped gnathosomal bay, the acetabular fields distinctly wider than long and with less than 100 + 100 acetabula, the narrow step-like extensions in the male genital area, P-2 with more than 4 mediodistal setae, P-4 with maximum H near distal margin, and slender P-5.

At the type locality, a female was found that agrees with the males of T. silvarum n. sp. in important details (anterior idiosoma shape, acetabula number, palp shape and setation), but differs in the presence of a well-developed dorsal furrow (measurements of this specimen:idiosoma L/W 760/640, W Cx-4-tips 620, gonopore L/W 115/120, genital field W 410, acetabular field W125. Palp measurements (L/H): P-1 33/35, P-2 93/75, P-3 60/63, P-4 102/67, P-5 52/20). Current investigations on the stream- and spring-dwelling Arrenurus -species will possibly help to identify the corresponding male – for the time being, we cannot exclude conspecifity with T. silvarum n. sp. (that would definitively destroy the concept of a monophyletic genus Thoracophoracarus ).

Figures

FIG. 9. — Thoracophoracarus silvarum n. sp., holotype ♂ (MNHN Ac1122): A, ventral idiosoma; B, palp. Scale bars: 100 μm.

FIG. 8. — Thoracophoracarus cooki n. sp., paratype ♂ (coll. Gerecke, Tübingen), SEM photographs: A, ventral view; B, lateral view; C, dorsal view; D, excretory pore and gonopore; E, excretory pore (detail of D). Scale bars: 100 μm.