Porobelba weigmanni, Miko, L., 2008

Miko, L., 2008, Taxonomy of European Damaeidae (Acari: Oribatida) II. Porobelba weigmanni n. sp. (Oribatida, Damaeidae), from East Slovakia, with comments on other known species of the genus, Zootaxa 1844 : 56-59

Porobelba weigmanni n.sp.

Diagnosis: Porobelba with characteristic, hypertrophied, lyriform notogastral setae c1 inserted on tubercular papillae; other notogastral setae very thin, minute. Prodorsum with one pair of tubercles (Da) behind insertions of interlamellar setae. Spinae adnatae acute, thorn-like, oriented slightly laterad and ventrad.

Description of the adult (immatures unknown)

General characters: Body 390-405 µm long (two specimens measured); as in other species of the genus covered by very thick layer of mostly filamentous cerotegument. Body colour brown or yellowish brown, as usual in the genus. Adults bearing reticulate exuvial scalps on the notogaster.

Prodorsum: Broadly triangular, without propodolateral apophysis P (Fig. 1A, 3A). Rostrum broadly oval, with small naso-like protuberance. Bothridia quite distant from notogaster (as usual for Porobelba ), funnel-like. Sensillus (Fig. 3C) medium long, setiform, covered by cerotegument except at tip. Interlamellar seta (in) relatively short, about one third of sensillus length, also covered by cerotegument. Exobothridial seta (ex) shorter than in, curved, hardly visible under cerotegument. Rostral and lamellar setae of similar size, in normal positions. One pair of prodorsal tubercles (Da) present behind insertions of setae in. Parastigmatic apophyses well developed, thorn-like, oblique, Sa larger than Sp.

Notogaster. Oval, with quite gracile, thorn-like spinae adnatae, oriented laterad and ventrad. Notogastral setae heterogeneous and characteristic: first pair of setae (c1) hypertrophied, oriented anteriad and curved mediad, creating lyriform shape (Figs. 1A, 3A), covered by cerotegument, inserted on small but distinct papilliform tubercles; other notogastral setae much shorter, thin, filiform, with size decreasing posteriorly. Area porosa between setae h1 well developed but quite small, oval (Fig. 3B). Setae ps2 longer than other posterior notogastral setae.

Ventral characters: Characters of ventral side (Fig. 1B) obscured by thick layer of cerotegument. Discidium (dis) ceratiform, slightly curved posteriad. Epimeral setation 3-1-3-3; setae similar in size to other ventral setae, except lateral ones slightly longer. Standard set of 6 genital, 1 aggenital, 2 anal and 3 adanal setae present, as usual in Damaeidae . Anogenital region with apertures well separated; genital only slightly smaller than anal.

Gnathosoma (Characters were studied only on non-dissected individuals, and therefore cannot be described in full detail): Type and form of gnathosoma as usual for Damaeidae . Chelicerae (Fig. 2D) robust, well sclerotised, both digitus fixus and digitus mobilis with strong tubercular teeth. Palps with elongated tarsus. Setation of palp (tarsal solenidion not included) 0-2-1-3-8, four distal setae on tarsus eupathidial (Fig. 2E).

Legs: Monodactyl and moniliform as usual in Porobelba , as long as or shorter than body, covered by cerotegument (Fig. 2 A-C), making setation difficult to study. Setal formula of legs identical to that of P. spinosa (see Norton 1977), as follows (solenidia and famulus not included):

I: 1-7-4-4- 19

II: 1-6-4-4- 17

III: 2-4-3-3- 16 IV: 1-4-3-4-13.

Solenidia quite short, except [[phi]]1 long, setiform, tactile. Solenidion of tibia IV coupled with seta d. Famulus emergent, short, simple, setiform.

Material examined: 2 individuals collected in Pieniny National Park, North-East Slovakia, in moist litter of Tilio-Acerion forests on limestone screes; with Tilia, Fagus, Acer and Phyllitis, on north-west slope of Klastorna hora hill , 18.4.1987, sample Nr. LM-190-87 (1 individual, paratype) and 21.8.1988, sample Nr. LM-319-88 (1 individual, holotype) , L.Miko lgt. Material is preserved unmounted, in ethanol. The holotype has been deposited in Acarological Collections of Staatliches Museum für Naturkunde Görlitz (Germany); the paratype is in the private collection of the author.

Discussion. The new species is easily distinguishable from other known species of Porobelba by the presence of prodorsal tubercles Da and by the unusual heterogeneity of notogastral setae. The lyriform setae c1 contrast strongly with the remaining notogastral setae which are smooth, fine and much shorter. The common type-species of the genus, P. spinosa , has setae c1 that are also larger than others, but are straight and parallel, oriented anteriad (Fig. 4A); other notogastral setae are shorter, but are about half the length of c1. The sensillus of P. spinosa (Fig. 4A, C) is relatively longer, and the prodorsum lacks tubercles. The Iberian species P. grandjeanica differs clearly by lacking spinae adnatae; other characters are very similar to those of P. spinosa (Grandjean 1954; Subías 1977).

Porobelba weigmanni n. sp. has been found in quite specific habitat, rich in many other oribatid species, in a cenosis dominated by Chamobates borealis ( Traegardh , 1902), Ch. voigtsi (Oudemans , 1902) and Parachipteria punctata (Nicolet , 1855), and together with some rather rare species such as Hungarobelba visnyai (Balogh , 1938) or Notophthiracarus (Calyptophthiracarus) pavidus (Berlese , 1913). Despite quite intensive sampling in Pieniny National Park, only two individuals were found, both from an unusual microhabitat: organic soil within the crevices in limestone scree on slopes. It is speculative to judge from two collections, but given this apparent specificity, and the fact that the Pieniny area was not glaciated in the last ice age, the species may be relictual. Although P. spinosa , occurs in Pieniny as well, it prefers more open habitats (meadows or meadows with shrubs, Juniperus sp. growths or drier litter of Pinus sylvestris forests) and the two species were never found together in the same sample nor the same habitat.

Another species has been described from Austrian Carinthia by Mihelcic (1955) and placed into this genus: Porobelba robusta Mihelcic , 1955. The original description and illustrations suggest that the species lacks some generic characters of Porobelba , including the notogastral porose area. In addition, the author claimed similarity of this species to Kunstidamaeus diversipilis (Willmann , 1951) (sub Belba diversipilis ), which belongs to a group of genera that can be considered Damaeus sensu lato. Although the figures are of low quality, it seems that P. robusta does have some characters found in this group but not in Porobelba . Collectively, the larger size, the similarity in length and shape of sensillus and interlamellar seta, the presence of a blunt apophysis P on the prodorsum, the slightly outwards curved spinae adnatae and the strong, curved notogastral setae indicate that P. robusta probably belongs to Spatiodamaeus Bulanova-Zachvatkina , 1967. There is superficial similarity to described species, e. g. Spatiodamaeus boreus (Bulanova-Zachvatkina , 1957), but there is no information about important species-level characters, such as various prodorsal tubercles. Therefore, P. robusta is here excluded from Porobelba , and until Mihelcic 's original material or topotypes are studied, we consider it as species inquirenda.

The last known species of the genus, Porobelba parki Jacot , 1937, is apparently restricted to eastern North America. Since the original description is incomplete and does not use modern terminology, some comments on this little known species are given in the following section.