Plekocheilus (Eurytus) juliani Haas, 1955

Breure, Abraham S. H. & Schlögl, Jan, 2010, Additional notes on Orthalicidae from the Chimantá massif, Venezuelan Guayana, with descriptions of new species of Plekocheilus Guilding, 1828 (Mollusca: Gastropoda), Zootaxa 2416, pp. 51-60 : 58-59

Plekocheilus (Eurytus) juliani Haas, 1955

Plecocheilus (Eurytus) juliani Haas, 1955: 375 , fig. 78. Type locality: Venezuela, State of Bolivar, northwest part of Chimantá massif, summit of Apacará-tepui, ca. 2100 m; holotype FMNH 49737.

Material. Venezuela, Estado Bolívar, Chimantá massif, Churí-tepui, 2130 m, J. Schlögl leg., ii.2009, RMNH 114247/1; ibidem, above central valley, B. Smida leg., ii.2009, RMNH 114248/ 1 juv. fragment. Both locality 3 on Fig. 1 C.

Remarks. The only adult shell collected is characterized by dark chestnut-brown lightning zig-zag stripes on the last whorl, bordered by a yellowish ‘shadow’ and is thus somewhat different in colour pattern than the type material (refigured in Breure 2009). However, the sculpture corresponds quite well to that of the types and the material is tentatively referred to this species.

H D HA WA LW W Plekocheilus (P.) vlceki spec. nov.

Holotype 309 177 159 100 261 40 RMNH 114234 322 172 158 100 272 42 Plekocheilus (Eurytus) breweri spec.nov.

During the expedition in February 2009, broken shells were found in one of the caves; the shells were located ca. 2 m under the nest of a bird ( Fig. 5 E). Although we have been unable to make direct observations of birds related to the presence of the shells, three bird species were spotted in the direct vicinity that could be candidates for ownership of the nest: the rufous-collared sparrow ( Zonitrichia capensis ), the tepui swift ( Cypseloides phelpsi ) and the white-collared swift ( Streptoprocne zonaris ). These are all known to occur on the Chimantá massif ( Huber 1992). It is, however, unlikely that the nest belongs to Z. capensis , as it is known to nest on the ground. The other two species are reported to nest on cliffs or other vertical walls, often in dark places ( Hilty 2002). Since C. phelpsi nests in colonies and the nest observed was the only one in the cave, it probably belongs to S. zonaris (M. Foster, pers. comm.). Further observations should clarify the relation between snails and birds.

Although this area is still undersampled, there is some evidence that most species are highly restricted in range. In terms of the IUCN categories and criteria for red-listing threatened species ( IUCN 2001), Plekocheilus vlceki and P. breweri are likely to meet the distribution-based criteria for listing as Critically Endangered. The same category (or the category Endangered) may apply to other land snails of the upper and highlands of Venezuelan Guayana ( Breure 2009, Simone in press, Thompson 2008). Currently, the Chimantá massif is part of the Canaima National Park ( Huber 1995c, Huber & Foster 2003), and—also due to the relatively inaccessability of the area—threats may not appear immediate. However, as Nogué et al. (2009) have shown, the tepui habitats are severely threatened under likely scenarios of climatic change. It is not clear yet how this will affect these snail species.

Prior to the discovery of the two new taxa described herein, three species of Plekocheilus were known from the Chimantá massif: P. fulminans alticola Haas, 1955 , P. juliani Haas, 1955 and P. mundiperditi Haas, 1955 ( Breure, 2009) . All taxa have been reported from the north-western part of the massif and the adjacent Auyán and Aparamán-tepuis. It is remarkable that the south-eastern part of Chimantá is home to two different taxa, while the nearest distance between the two parts is only ca. 3 km ( Fig. 1 B). The occurrence of P. juliani needs further corroboration. The relationships between the nominate taxon P. fulminans (Nyst, 1845) (occurring in northern Venezuela) and the Guayanan subspecies need further clarification. A preliminary morphometric analysis casts some doubts on the subspecific status of the Guayanan taxon. However, the number of specimens available is too low to make a statistical analysis possible.

While mollusc collecting in this area was done until now as a side-line, the findings reported in this paper show that a focussed search may yield additional taxa and may improve our understanding of the ecology in this ecosystem. It is expected that further collecting on these and other tepuis may reveal additional new taxa and further enhance our knowledge of this fascinating habitat.

Figures

FIGURE 5. Habitat and localities of Plekocheilus species treated in this paper. A. Aerial view of Churí-tepui and surroundings from the North-east. B. Brocchinia with a flowering Utricularia humboldtii inside. C. Habitat of P. breweri spec. nov., showing Bonnetia trees. D. Snail inside Brocchinia hechtioides. E. Bird nest in Cave Juliani where empty shells of P. breweri were found on the ground below. F – G. Overview of Sima Nor-oeste, type locality of P. (P.) vlceki spec. nov.

FIGURE 1. A. Map of northern South America, showing Venezuelan Guayana (white rectangle) and Chimantá massif (white dot). B. Map of Chimantá massif, showing location of tepuis (modified after Huber 1995 a). C. Churí-tepui. The three locations studied are indicated by arrows.