Mexicenotica xochii, Grego, Jozef, Angyal, Dorottya & Beltran, Luis Arturo Lievano, 2019

Grego, Jozef, Angyal, Dorottya & Beltran, Luis Arturo Lievano, 2019, First record of subterranean freshwater gastropods (Mollusca, Gastropoda, Cochliopidae) from the cenotes of Yucatan state, Subterranean Biology 29, pp. 79-88 : 81-82

Mexicenotica xochii sp. n. Figures 3-10

Diagnosis.

The shell shape of the new species closely resembles subterranean species belonging to family Pomatiopsidae from Laos ( Tricula valenasi Grego, 2018 and Tricula spelea Grego, 2018), and the fine fragile faintly corrugated aperture margin is reminiscent of some cave dwelling specimens of pomatiopsid Spiripockia punctata ( Simone 2012) from Brazil. However, the geographical distance and absence of pomatiopsid species hitherto known from the Yucatán region rather suggest the resemblance in the shell shape of a cochliopid species. From the geographically close Cochliopidae species, the closest resemblance in the shell shape is found in the Mesoamerican genus Aroapyrgus H.B. Baker, 1931 ( Aroapyrgus pasionensis (Goodrich & Van der Schalie, 1937) from Alta Verapaz, Guatemala), but the new species differs by its more elongated conical shape, with a less prominent body whorl and a proportionally smaller aperture. Furthermore, the aperture of M. xochii sp. n. is expanded and finely marginated by a tiny, corrugated structure, while A. pasionensis has a rather smooth peristome.

Type locality.

Mexico, Yucatán state, Cenotillo Municipality, Cenote Xoch, at 46m deep by SCUBA dive, inside cave sediments, 20,997565°N; 87,936659°W.

Type material.

Holotype, Type locality: leg. Angyal and Liévano, 5 Jan. 2017. (HNHM 104156). Paratypes, same data (coll. Grego 1 specimen); type locality, leg. Angyal and Liévano.

Measurements.

Holotype: H 1.84 mm; W 1.05 mm; WB 0.85 mm; AH 0.74, AW 0.56 (holotype). Figs 3-6. Paratype: H 1.82 mm; W 1.08 mm; WB 0.87 mm; AH 0.74, AW 0.56 (holotype). Figs 7-10.

Etymology.

Derived from the type locality in Cenote Xoch, Cenotillo municipality, Yucatán state, Mexico.

Description.

The snow-white elongate-conical shell with five rounded slightly convex whorls with a weak suture and a blunt apex. The surface smooth and shiny with very faint, almost invisible, transverse growth lines. Aperture elongate oval, ear-shaped, adapically, separated from the body whorl by a weak furrow. The peristome margin expanded, and its reflexed outline bordered by a slightly corrugated, thin and fragile collar. The columellar lip very slightly wavy in its lateral plane, the outer lip straight. Umbilicus closed and obscured.

Habitat.

The cenote Xoch is a deep vertical cavern (Fig. 2.) with abundant sediments of plant debris found up to its depth at more than 70m. The cave system has one shallower and a deeper horizontal cave passage at 21m and more than 50m, respectively. The water temperature is 25°C. The organic material deposited in the cenote has two main resources: the epigean decaying dead plants and the belt of indigenous live green algae alongside the cavern walls from the water surface down to 11m depth. The sample with empty shells was taken during dive into 53m depth and at 400m horizontal cave passage. It was taken from a thick organic sediment deposited at 46 m depth. Inside the same sample, specimens of minute bivalvians of cf. Pisidium sp. and a few specimens of ostracods were also found. During the research dive, individuals of stygobiont crustaceans, such as Antromysis cenotensis Creaser, 1936, Creaseriella anops (Creaser, 1936), and Typhlatya sp. were also collected at the free water column of the cavern. Trichoptera and Plecoptera larvae, as well as ostracods and water mites were collected in the green algae layer from the cave walls.

Distribution.

Only known from the type locality. Within the type locality the new species was found together with the Pyrgophorus thompsoni sp. n., and cf. Pisidium sp.

Remarks.

Due to absence of molecular and anatomical data, the proposed positioning of the new genus in the family Cochliopidae is only provisional, based on the closest resemblance to the geographically closest relatives, but the overall shell shape with flaring margin shows some resemblance also to the Southeast Asian and Brazilian members of the family Pomatiopsidae , which have no close geographical analogue in the region. The new species rather represent by its shape an evolutionary resemblance of a cochliopid species induced by the similar environment to that of the Pomatiopsidae .