Metabelba pulverosa Strenzke, 1953

van der Hammen, L. & Strenzke, K., 1953, A Partial Revision of the Genus Metabelba Grandjean (Oribatei, Acarina), Zoologische Mededelingen 32, pp. 141-154 : 148-152

Metabelba pulverosa Strenzke nov. spec. (figs. 5, 6)

Length of the idiosoma 425-495 µ; length of the propodosoma 190 µ, of the hysterosoma 305 µ; breadth of the hysterosoma 305 µ. Colour glossy brown. Generally the specimens are strongly covered with cerotegument. Often the adults bear the larval and nymphal skins. Rostral hairs, lamellar hairs, interlamellar hairs, and exobothridial hairs slightly coarse; the remaining hairs and the sensillus are smooth.

Propodosoma between the f irst and the second legs with a strong anterior apophysis that is directed to the front, and that is distally truncate or sometimes slightly excavated; the surface of the apophysis is granulate (a.a. in figs. 5, 6a). Anterior parastigmatic apophysis (a.p.a.) slender and conical, directed sideways and upward. A similar, but shorter apophysis in front of acetabulura III (posterior parastigmatic apophysis, a.p.p.) and in front of acetabulum IV (discidium, dis).

Posterior border of the propodosoma without protuberances. In front of the bothridium, at each side, at first a round, light spot, then an area of smaller irregular spots. A similar, unpaired group occurs just between the bothridia. Medially and anally of the bothridia at each side a single light spot, posteriorly of which the chitin is slightly thickened, without, however, forming a protuberance as in related species. The disposition of the propodosomatal hairs is shown in figs. 5a, 6a. The sensillus (length about 120 µ) is flagelliform; it is directed obliquely backward. The interlamellar hairs (length about 80 µ) are also directed obliquely backward; they stand close to the bothridia. Bothridium cup-shaped. Exobothridial hairs close to the antiaxial side of the bothridia; they are strongly curved, and are directed frontward and upward.

Notogastral hairs in two rows, each of 8 curved hairs, which are inserted rather close to each other. The two anterior pairs (c1 and c2) are directed to the front, the remaining hairs 'backward (figs. 5a, 6a). Three pairs of hairs occur at the posterior border of the notogaster (ps1, ps2, ps3 in figs. 5b, 6 a). The hairs of the two longitudinal rows possess wing-like expansions that begin just above the base; these are especially striking in the hairs c1 and c2 (fig. 6b). In baisam these features become less distinct. Length of the hairs c1 and c2 80 µ; the remaining notogastral hairs are about 60 µ long. The disposition of the fissures on the notogaster is shown in fig. 6a. There are no Spinae adnatae.

Genital and anal plates separated by a large interval. The chaetotaxy of the ventral surface is shown in fig. 5b.

The shape and the chaetotaxy of the legs is shown in figs. 6c, d. The number of hairs is as follows:

On femur I dorsally a strong, serrate hair that is curved to the front close above the base. On leg IV similar hairs on trochanter, femur, and genu. The remaining hairs of the legs partly with similar expansions as the notogastral hairs. Solenidion of tibia IV free, and strongly curved in the middle. The length (in µ) of the joints of the legs is. as follows:

Holotype: from the soil of a forest meadow at the Keller See , Holstein, 18.V.1940 (sample 239, cf. Strenzke, 1952, p. 48), as slide in Strenzke's collection. Paratypes from the same sample , in alcohol, in the collection of the Rijksmuseum van Natuurlijke Historie, Leiden, and in Strenzke's collection.

It is difficult to establish the synonymy of the species because of the absence of reliable figures. An essential part of the records of M. pulverulenta from Central Europe may refer to M. pulverosa . According to the description and figure reproduced by Oudemans (1937, p. 2595, fig. 1117) it is, anyhow, impossible to identify Koch's species with certainty, because at present it is evident that the genus Metabelba consists of a rather large number of species that are difficult to distinguish. As Koch's species is characterized by the absence of an anterior apophysis between I and II, and by the occurrence of laterally inserted notogastral hairs that surpass the border of the notogaster ("Hinterleib ... mit einer Reihe kurzer, gekrümmter, spitzer Borsten über den Seiten und über dem Hinterrande"), the identity of pulverulenta and pulverosa is not probable. As far as concerns the possibility of Koch's species being a Porobelba , cf. Grandjean (1936, p. 67), van der Hammen (1952, p. 41), Strenzke (1952, p. 101).

It is difficult to identify Kulczynski's Oribata pulverulentus (1902, p. 35). Habitus and measurements (legs!), as well as the absence of protuberances on the propodosoma, point to the identity with pulverosa . There are, however, important differences in the chaetotaxy of the legs, in the number of hairs (according to Kulczynski there is only one hair on trochanter IV), as well as in their shape (Kulczynski does not figure strongly serrate dorsal hairs on the proximal joints) (cf. Kulczynski, 1902, pl. 4 figs. 60, 61).

Turk's Porobelba pulverulenta (Turk and Turk, 1952) appears to be a species of Metabelba ; the slide is, however, too damaged to be identified with certainty; possibly it concerns a species not dealt with in the present revision 1).

It is impossible to draw conclusions concerning the geographical distribution of M. pulverosa . For a certainty the species is up till now only known from Germany (Holstein, Pomerania, Westphalia). Probably Willmann's records (1931, p. 120) also refer to the species. In northern Germany M. pulverosa prefers localities with a strongly developed litter layer; the species is not rare in forest meadows, alder marshes, coniferous and deciduous woods, but it also occurs under Ericaceae in moorlands; it avoids, however, bogs (Sphagneta) (cf. Strenzke, 1952, p. 102 sub pulverulenta ).

It is a striking fact that M. papillipes , evidently not rare in the Netherlands, was not yet discovered in Germany, whilst on the other hand M. pulverosa was not yet found in the Netherlands.

1) The diagnosis of the specimen is as follows. Length 625 µ; colour light brown; the cerotegument is thin and slightly granulate. Notogastral hairs coarse and rather short; apart from one or two anterior pairs they are strongly curved. The measurements of the legs correspond exactly with those of the montana specimen studied by us. Possibly Turk's specimen is indeed identical with montana ; the light colour and the different cerotegument may be due to the fact that at the date of its capture it had just become adult.