Phreatoviesca spinosa Czaja & Gladstone, 2021

Czaja 1, Alexander, Gladstone 2, Nicholas S., Becerra-Lopez 1, Jorge Luis, Estrada-Rodriguez 1, Jose Luis, SaenzMata 1, Jorge & Hernandez-Teran 3, Fernando, 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, pp. 129-141 : 129

Phreatoviesca spinosa Czaja & Gladstone sp. nov.

Figs 2-13 , 14-17 , 18-24

Type locality.

Mexico, Coahuila state, Viesca , spring “Túnel 7" (25°20'38"N, 102°54'19"W, 1102 m a.s.l.) (Fig. 1 ).

Types.

Holotype (Figs 2 , 3 ), UJMC 500, from type locality, leg. A. Czaja, 15/v/2019. Paratypes, UJMC 501-511, from same lot, >100 dry shells.

Etymology.

Name is derived from the Latin word Phreatoviesca spinosa = having spines.

Referred material.

Coahuila. Viesca , Spring “Túnel 7", UJMC 500-511, A. Czaja, J. L. Estrada-Rodríguez 10/vi/2015 and 15/v/2019.

Diagnosis.

Like for the genus.

Description.

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 3 , 6 ), suture deep; teleoconch sculptured with irregular, strong marked growth lines and with ribs (Figs 4 , 5 ), spiny shells with whorls with a peripheral slightly pronounced carinae, ribs at the carina are modified into regularly spaced shovel-shaped spines (Figs 14 , 24 ), transition protoconch/teleoconch distinct, marked by a change in surface texture from pitted to axial growth lines, whorls rapidly increasing in diameter, first two whorls smooth, without carina or spines, the last three whorls with increasing number spines (up to 40 on the body whorl, but usually less than 30), spiral lines beginning at the end of protoconch, a few specimens with smooth whorls without any sculpture but with thickened axial growth lines, some (smooth) specimens with a varix just behind the aperture (Fig. 13 ), body whorl large, apertures large, ovate to subrounded, often trumpet-like (Fig. 9 ). Protoconch with coarsely honeycomb-like pits, the basal and outer lip rounded and thin, some smooth specimens with trumpet-like peristome, umbiculus deep or, in corkscrew-like specimens, almost without umbiculus; Opercula not preserved. Shell measurements (mean ± standard deviation in parentheses; n = 17): SH 2.08 (0.31) mm, SW 1.24 (0.17) mm, AH 0.79 (0.09) mm, AW 0.61 (0.08) mm, WN 4.93 (0.44) whorls; HBW 1.23 (0.21) mm. Paratypes from the type locality.

Measurements of holotype.

WN 5¼ whorls; SH 2.26 mm; SW 1.41 mm; AH 0.86 mm; AW 0.67 mm, HBW 1.46 mm.

Habitat.

The new species was found exclusively in one spring near Viesca , Coahuila. The original habitat was probably the outlet of a cave, were the species likely inhabited interstitial waters.

Distribution.

A microendemic species, only in spring “Túnel 7", near the town of Viesca .

Remarks.

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 Phreatoviesca gen. nov. et. sp. nov. from shells of all other described stygobiotic gastropods in North America. We considered these shell features as derived characters (apomorphy) of a new clade, most likely within the family Cochliopidae . The SEM imagines of the two different morphotypes (smooth and spinous) from Viesca show that both have identical coarsely honeycomb-like pitted protoconchs (Figs 18 , 19 ) and also the details of the shell wall microstructure with fine growth lines are similar (Figs 22 , 23 ). Therefore, we consider these two morphotypes as belonging to the same species. There is no significant difference in shells measurements between smooth and spiny morphotypes and therefore sexual dimorphism is unlikely. Moreover, most of the shells have strong spines and only less than 5% of the morphotypes collected are smooth. Two morphotypes (one smooth and other with lamelliform costae) not associated with sexual dimorphism, were reported also from shells of the subterranean genus Paludiscala Taylor, 1966, described from the neighboring Cuatro Ciénegas Basin (Hershler, 1985). Interestingly, our material is conchologically similar to members of the stygobiotic and stygophilic genus Pyrgophorus Ancey, 1888 in Mexico, which show similar shovel-shaped spines ( Grego et al. 2019). This resemblance is surely an evolutionary convergence and result from living in subterranean habitats.

Figures

Figure 1. Map of the study area with localization of the sampling site near the town of Viesca, Coahuila, Mexico.

Figures 2 - 13. Shells of Phreatoviesca spinosa gen. nov. et sp. nov. 2, 3 holotype, specimen from both sides, UJMC 500 4, 5 paratype 1, specimen from both sides, UJMC 501 6 paratype 2, specimen with a ' corkscrew' - like morphology, UJMC 502 7, 8 paratype 3, specimen from both sides, UJMC 503 9 paratype 4, specimen with smooth whorls and a trumpet-like aperture, UJMC 504 10, 11 paratype 5, specimen with smooth whorls, UJMC 505. Opercula 12, 13 paratype 5, specimen with smooth whorls, UJMC 505. Scale bar: 1 mm.

Figures 14 - 17. SEM images of Phreatoviesca spinosa gen. nov. et sp. nov. 14 specimen with strong spines, UJMC 506 15 specimen with ribs, UJMC 507 16 specimen with smooth whorls, UJMC 508 17 specimen with smooth whorls, UJMC 509. Scale bar: 1 mm.

Figures 18 - 24. SEM images of Phreatoviesca spinosa gen. nov. et sp. nov. 18 shell apex with protoconch, UJMC 508 19 paratype 3, shell apex with protoconch, UJMC 503 20 shell apex with protoconch, UJMC 510 21 paratype 1, apex with protoconch, UJMC 501 22 smooth specimen with body whorl shows irregular, strong marked growth lines, UJMC 508 23 paratype 1, body whorl shows irregular, strong marked growth lines, UJMC 501 24 paratype 2, body whorl shows regularly spaced shovel-shaped spines, UJMC 502.