Monacha (Paratheba) claussi, Hausdorf, 2000

Hausdorf, Bernhard, 2000, genus Monacha in the Western Caucasus Gastropoda: Hygromiidae), Journal of Natural History 34, pp. 1575-1594 : 1576-1580

Monacha (Paratheba) claussi , sp. n.

(®gures 1, 10, 17)

Shell (®gure 1). Strongly depressed conical±globular; with 5ì±5× convex whorls; teleoconch with wrinkled growth-ridges and Ô distinct incised spiral striae; whitish; body whorl rounded; aperture almost circular; upper insertion of the peristome slightly descending; peristome sharp, hardly expanded, with a whitish internal rib; umbilicus moderately wide, hardly obscured by the reēcted columellar edge.

Measurements. Gorge between Monastyrka and Kepsh (n 5 30): D: 16.4± 20.9 mm, x Å 5 18.6 mm; H: 8.7±11.7 mm, x Å 5 10.4 mm; D/H: 1.60±1.96, x Å 5 1.79.

Genitalia (®gure 10). The penial papilla is very long. The long and slender basal section of the appendicula is delimited from the short, hardly expanded apical section by an indistinct narrowing. The two slightly rami®ed glandulae mucosae insert at the proximal end of a distinct muscular swelling of the vagina. The bursa of the bursa copulatrix is oval or Ô rounded triangular. In two specimens examined the right ommatophoral retractor crosses with the penis, in one it crosses only with the penial retractor. The measurements of some sections of the genitalia are compiled in table 1 and the variation of the proportions of some sections of the genitalia is compiled in table 2.

Remarks. M. claussi diOEers from all other Caucasian Monacha species in the large, strongly depressed shell with a comparatively wide umbilicus.

The shell of M. claussi resembles M. (Metatheba) subcarthusiana (Lindholm) which lives in less steep regions of the gorge between Monastyrka and Kepsh. However, the shell of M. claussi is larger, more depressed and has a slightly wider umbilicus than the shell of M. subcarthusiana .

M. (Paratheba) claussi and M. (Metatheba) subcarthusiana are the only Monacha species in which the right ommatophoral retractor crosses with the penis in some specimens. The course of the right ommatophora l retractor has changed often within the Stylommatophora . Nevertheless, there are only a few species which are polymorphic with regard to this character (e.g., Krynickillus urbanskii (Wiktor) , see Wiktor 1971). The crossing with the penis is the plesiomorphic character state. There are three possible interpretations of the ®nding that two Monacha species of diOEerent subgenera are polymorphic with regard to the course of the right ommatophoral retractor: (1) the ancestor of Monacha was polymorphic with regard to this character and the free course of the retractor became ®xed independently several times; (2) the crossing in some specimens of M. claussi and of M. subcarthusiana is an atavism; (3) M. claussi and M. subcarthusiana are the most basal Monacha species and the course of the retractor became ®xed only once in the ancestor of all other Monacha species. If (3) were true, Paratheba, of which no autapomorphies are known, would be paraphyletic and Metatheba , which is characterized by the loss of the appendicula, would be polyphyletic. Actually, it has been shown that the appendicula has been reduced several times convergently in Monacha (Hausdorf, in press).

Etymology. This species is named in honour of Prof. Dr Eberhard Clauss,

Quedlinburg, who discovered it and recognized it as an unknown species. Type locality. Russia: gorge between Monastyrka and Kepsh, EJ82 . Distribution and material (®gure 17). M. claussi is known only from the

Mzymta valley . Russia. Gorge between Monastyrka and Kepsh, EJ82 (det. anat.; holotype ZMH

2765, leg. E. Clauss 28 May 1984, measurements: D 5 19.1 mm, H5 10.4 mm; CLA;

ZMH 2766); Gora Aishkha, subalpine zone, FJ23 (det. anat.; ZMUM 19099).