Additional notes on Orthalicidae from the Chimantá massif, Venezuelan Guayana, with descriptions of new species of Plekocheilus Guilding, 1828 (Mollusca: Gastropoda)
Author
Breure, Abraham S. H.
Author
Schlögl, Jan
text
Zootaxa
2010
2416
51
60
journal article
10.5281/zenodo.293891
97ad8d73-38ac-49a8-80f6-24a598667875
1175-5326
293891
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.
TABLE 1.
Measurements of species described in this paper. Abbreviations: D, shell diameter; H, shell height; HA, height of aperture; LW, height of last whorl; W, number of whorls; WA, width of aperture.
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.
Holotype |
417 |
220 |
220 |
136 |
356 |
41 |
RMNH 114236 |
372 |
211 |
203 |
126 |
326 |
40 |
RMNH 114236 RMNH 114236 |
379 394 |
207 212 |
203 212 |
127 130 |
324 337 |
42 39 |
RMNH 114236 |
383 |
211 |
207 |
131 |
324 |
41 |
RMNH 114236 RMNH 114239 |
392 385 |
214 208 |
207 205 |
130 130 |
337 330 |
43 42 |
Discussion |
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.