Corresponding author: José Luis Estrada-Rodríguez (
Academic editor: Jozef Grego
This paper describes a new genus and species of subterranean gastropod from a karstic region near
Czaja A, Gladstone NS, Becerra-López JL, Estrada-Rodríguez JL, SáenzMata J, Hernández-Terán F (2021) A remarkable new genus and species of subterranean freshwater snail from a recently dried-up spring of Viesca, Coahuila, Northern Mexico. Subterranean Biology 39: 129–141.
Owing to sampling difficulty associated with subterranean habitats, it is not surprising that stygobiotic (i.e., freshwater subterranean-obligate) gastropods are among the most understudied freshwater groups in the world (
Although mollusk shells generally have a high fossilization potential, there are few records of gastropod fossils that have been determined to be stygobionts worldwide. This fossil scarcity is likely owing to the usually narrow geographic distributions of stygobiotic gastropods, along with their extremely small size that does not typically exceed two millimeters (
The aim of the present study is to describe a new subterranean genus and species from Coahuila, and to discuss unique aspects of the shell morphology compared to other stygobiotic gastropod species in North America. The new genus can be readily distinguished by three shell features: (i) prominent open coiling of the last whorl, (ii) shovel-shaped spine ornamentations on the teleoconch, and (iii) coarsely honeycomb-like pitted protoconch structure. Although the description of both genus and species based exclusively on shell morphology may appear erroneous, the shell features of the discovered specimens are so strikingly different from all known stygobiotic gastropods that we consider the erection justified. Nevertheless, in the absence of soft parts, the family designation is tentative until living specimens will be obtained for anatomical and molecular studies.
The studied shells were collected during July 2015 and November 2019 in two sites within the spring “Túnel 7” (Fig.
Map of the study area with localization of the sampling site near the town of
The collected material was screened through two sieves with a mesh size of 0.5 mm and 0.3 mm. For the morphological analysis, the shells were photographed and measured with a Zeiss AxioCamERc 5s camera attached to a Zeiss Stemi 2000-C microscope. Some specimens, particularly their protoconchs, were examined in the Laboratory of Biotechnology, Universidad Autónoma de Coahuila (
We obtained the following shell morphometrics for each specimen collected (excluding ratios): total number of whorls, shell height, shell width, aperture height, and aperture width. The mean, standard deviation and sample size are given in text (shell measurements). Shell whorls were counted according to the method of
Abbreviations used for shell morphometrics are as follows:
Shell small, conical in form, protoconch sculptured with coarsely honeycomb-like pits, teleoconch with curved ribs which are at the carina modified into regularly spaced shovel-shaped spines (Figs
The characteristic combination of three aforementioned shell features (open coiling of the last whorl, shovel-shaped spines, and protoconch with coarsely honeycomb-like pits) separate the new genus clearly from shells of all other subterranean (and epigean) genera. Some members of
The name is derived from Greek
Mexico, Coahuila state,
Holotype (Figs
Name is derived from the Latin word
Coahuila.
Like for the genus.
Shell small, conical, white or colorless, sometime with rests of light brown periostracum, yielding diversity in shell form, with 4–5½ rounded whorls (usually 5), whorls increasing in radius, the first three whorls never uncoiled, subsequent whorls open coiled, body whorl always uncoiled, some specimens show a ‘corkscrew’-like morphology (Figs
Shells of
The new species was found exclusively in one spring near
A microendemic species, only in spring “Túnel 7”, near the town of
The open coiled last whorl, shovel-shaped spines and a protoconch with coarsely honeycomb-like pits are the most evident characteristics which differentiated the shells of
The general turriform shell shape of
Regarding the open-coiling shell morphology, it seems as though
The prominent spine ornamentations of
An openly coiled shell is a rather atypical character among gastropods, but occurs in both marine and continental (freshwater and terrestrial) groups across many independent lineages since the earlier Paleozoic (
Several of these hypotheses were discussed in detail by
Clearly the wide range of potential mechanisms that may drive open coiling makes narrowing down on any one a difficult task, and all of these hypotheses require much additional study (particularly
Although we cannot validate any hypothesis with certainty for
We thank M.C. Inty Omar Hernández de Lira, Universidad Autónoma de Coahuila (