Research Article |
Corresponding author: Gabriel Fernando Cardoza-Martínez ( gfcm2115@gmail.com ) Academic editor: Oana Teodora Moldovan
© 2019 Alexander Czaja, Gabriel Fernando Cardoza-Martínez, Iris Gabriela Meza‑Sánchez, José Luis Estrada-Rodríguez, Jorge Saenz‑Mata, Jorge Luis Becerra-López, Ulises Romero-Méndez, Josué Raymundo Estrada‑Arellano, Miguel Ángel Garza-Martínez, José Antonio Dávila Paulín.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Czaja A, Cardoza-Martínez GF, Meza-Sánchez IG, Estrada-Rodríguez JL, Saenz-Mata J, Becerra-López JL, Romero-Méndez U, Estrada-Arellano JR, Garza-Martínez MA, Paulín JAD (2019) New genus, two new species and new records of subterranean freshwater snails (Caenogastropoda; Cochliopidae and Lithoglyphidae) from Coahuila and Durango, Northern Mexico. Subterranean Biology 29: 89-102. https://doi.org/10.3897/subtbiol.29.34123
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This paper describes a new genus, two new species and new records of subterranean gastropods from the Sabinas and Álamos River, Coahuila, and the Nazas River, Durango, in northern Mexico. Phreatomascogos gregoi gen. n. et sp. n. from Don Martín Basin, Coahuila, is described based on shells and opercula that show some morphological similarities with shells of Phreatodrobia Hershler & Longley, 1986 (Lithoglyphidae), which is a subterranean genus from neighboring area in Texas, United States. Conchologically, the new genus can be distinguished from Phreatodrobia and all other subterranean genera by a unique combination of characteristic shell morphology and opercula apomorphies. Balconorbis sabinasense sp. n. (Cochliopidae) is the second species of this genus, which was previously known only from caves and associated subterranean habitats in Texas. The new record of Coahuilix parrasense, Czaja, Estrada-Rodríguez, Romero-Méndez, Ávila-Rodríguez, Meza-Sánchez & Covich, 2017 (Cochliopidae) from Durango and Coahuila is the first record of extant member of this genus out of its hitherto known habitat in the Cuatro Ciénegas basin, Coahuila. These records are remarkable because C. parrasense had been described recently as a fossil species. Shell morphologies of the new subterranean snails could be interpreted as possible evolutional adaptations to different hydrodynamic and other specific conditions in their habitat.
Gastropods, phreatic, North America, systematics, interstitial habitat, shell adaptations
Compared to worldwide biodiversity hotspots as the Balkans (Sket, 2012), the North American subterranean snail fauna is not very rich in known species, including only 39 species of 17 genera (Hershler and Longley 1990;
The aim of the present study is to describe the new subterranean snails from Coahuila and Durango, compare similarities and differences to their known relatives from Cuatro Ciénegas and Texas and to briefly discuss their shell adaptations. Like many of the worldwide subterranean snails, also the present new Balconorbis species was described based exclusively on shell morphology, in the case of Phreatomascogos gen. n., on shell and operculum morphology. Therefore, especially the family assignation of the new genus is tentative until living specimens will be obtained for anatomical and molecular studies. The present investigations form part of a broader study of fossil and extant land and freshwater molluscs from North Mexico, which began in 2013 and includes research on systematics, ecology and evolution (
The studied subterranean snails were collected during July and November 2018 in nine sites along the Sabinas/Álamos River, Don Martín Basin, Coahuila and in one site on the Nazas River, northeastern Durango, Mexico (Fig.
Sampling localities with geographical coordinates, altitudes and occurrences of Phreatomascogos gregoi gen. n. et sp. n., Balconorbis sabinasense sp. n. and Coahuilix parrasense Czaja, Estrada-Rodríguez, Romero-Méndez, Ávila-Rodríguez, Meza-Sánchez & Covich, 2017 in the study area.
Locality | P. gregoi | C. sabinasense | C. parrasense | Coordinates | |
1. Sabinas River, Ejido Nacimiento de los Mascogos II | X | 101°42'46''W, 28°00'25''N | |||
2. Sabinas River, Ejido Santa María | X | X | 101°25'16''W, 27°58'37''N | ||
3. Sabinas River, Ejido Sauceda del Naranjo | X | 101°22'04''W, 27°57'24''N | |||
4. Sabinas River, Ejido San Juan de Sabinas | 101°17'54''W, 27°55'06''N | ||||
5. Álamos River, Ejido Paso del Coyote | X | X | 101°15'19''W, 27°56'45''N | ||
6. Sabinas River, Las Adjuntas (Rancho San Carlos) | X | X | 101°11'41''W, 27°53'33''N | ||
7. Sabinas River, Sabinas (Agua Prieta) | X | X | 101°06'06''W, 27°49'38''N | ||
8. Sabinas River, Las Cazuelas | 101°03'14''W, 24°47'42''N | ||||
9. Sabinas River, La Vega | X | X | 100°57'10''W, 27°41'35''N | ||
10. Nazas River, Los Cuates (Durango) | X | 103°42'13"W, 25°27'56"N |
We used following shell morphometric dataset (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
The studied material is deposited at the Malacological Collection of the Faculty of Biological Science of the Juarez State University of Durango and at the National Collection of Molluscs, National Autonomous University of Mexico (CNMO).
Abbreviations used: WN, total number of whorls; SH, shell height; SW, shell width; AH, aperture height; AW, aperture width; HBW, height of body whorl; UJMC = University Juárez Malacological Collection.
Phreatomascogos gregoi sp. n. by present designation.
Shell small, valvatiform to low trochoid; transparent to whitish; teleoconch with one or two prominent, sometimes almost winged keels; umbilicus almost completely covered (bordered) by a basal keel-like structure; operculum near circular, paucispiral, strongly campanulate.
The characteristic combination of mentioned three shell features (bordered umbilicus, prominent keels and strong campanulate operculum) separate the new genus clearly from shells of all other subterranean genera. Similar in size and general form are only shells of some members of Phreatodrobia Hershler and Longley from Texas, a genus which includes exclusively subterranean species. Nevertheless, none species of this genus possess keeled shells with a bordered umbilicus, smooth protoconch and such trochoid elevated opercula. The monotypic, recently erected (based on shell morphology) genus Novalis Quiñonero-Salgado & Rolán, 2017 (Hydrobiidae) from Spain resembles in some details the material from Coahuila (
The genus name derives from the word phreatos (referring to the subterranean habitat) and from Mascogos, an afrodescendant ethnic group of Coahuila which escaped the threat of slavery in the United States and lives since 1852 in the Sabinas/Álamos River area.
MEXICO, Coahuila state, Don Martín Basin, Álamos River, Ejido Paso del Coyote (101°15'19"W, 27°56'45"N, 369 m a.s.l.) (Fig.
Holotype (Figs
Shells and opercula of Phreatomascogos gregoi gen. n. et sp. n. 2, 3 holotype, UJMC 400 4, 5 paratype 1, UJMC 401 6, 7 paratype 2, UJMC 401a, shell apex with protoconch 8 umbilicus almost completely covered by a basal keel, UJMC 401b 9 paratype 3, UJMC 401d, conical specimen 10, 11 opercula 11 operculum showing the strongly campanulate shape. Scale bars: 0.5 mm (2–5, 9–11); 0.3 mm (8).
Named after Dr. Jozef Grego, a well renowned Slovakian malacologist and specialist of subterranean snails.
COAHUILA. Don Martín Basin, Sabinas/Álamos River, UJMC 402, Ejido Nacimiento de los Mascogos II, Y. A. Sanchez-Montañez, 03/vii/2018. UJMC 403, Ejido Santa María, Y. A. Sanchez-Montañez, 03/vii/2018. UJMC 404, Ejido Sauceda del Naranjo, Y. A. Sanchez-Montañez, 08/vii/2018. UJMC 405, Las Adjuntas (Rancho San Carlos), Y. A. Sanchez-Montañez, 08/vii/2018. UJMC 406, Sabinas (Agua Prieta), Y. A. Sanchez-Montañez, 08/vii/2018. UJMC 407, La Vega, Y. A. Sanchez-Montañez, 08/vii/2018.
The colorless, translucent to whitish shells are very small, valvatiform to low trochoid, umbilicate, with 3¾ or fewer rounded whorls; aperture near-circular, adnate to the bodywhorl; operculum paucispiral, strongly campanulate; teleoconch with bodywhorl which frequently has one or two, in some specimens winged, keels; umbilicus almost completely covered by a basal keel-like structure.
Shell small, valvatiform, varying in shape from (mostly) flat-trochoid to (rarely) low conical, height 0.65–0.99 mm (1 trochoid shell of 1.42 mm considerably higher, Fig.
(mean ± standard deviation in parentheses; n = 16): SH 0.84 (0.09) mm, SW 1.36 (0.08) mm, AH 0.57 (0.07) mm, AW 0.55 (0.06) mm, WN 3.05 (0.19) whorls; HBW 0.72 (0.10) mm. Paratypes from the type locality.
SH 0.86 mm; SW 1.38 mm; AH 0.52 mm; AW 0.56 mm, WN 3.00 whorls; HBW 0.73 mm.
Stygobiotic. Shells of Phreatomascogos gregoi n. sp. were collected on the shore of the river in sandy and clayed sediments with many gravels on the bottom. We suppose, the new species likely inhabits the interstitial waters within the water saturated underground gravel layer of the hyporheic zone (see below). Although the habitat of Phreatomascogos lays within one of the eight federal protected zones APRN (=Mexican Protected Natural Resource Areas), their habitat may be threatened (especially the sites Ejido Sauceda del Naranjo and Ejido San Juan de Sabinas) by local coal mining and agriculture.
Phreatomascogos gregoi sp. n. lives likely sympatrically with B. sabinasensis sp. n. (see below) in same subterranean, interstitial habitat. The species appears to be endemic to the Sabinas/Álamos River, Don Martín Basin, between the upper basin and Venustiano Carranza dam.
The typical strong keels, the almost completely covered umbilicus structure and the strongly campanulate operculum are the most evident characteristics which differentiated the shell morphology of Phreatomascogos gregoi sp. n. from the shells of all other described subterranean gastropods. A North American subterranean species conchologically most closely related to our material is Phreatodrobia nugax Hershler & Longley, 1986 from South-Central Texas. This species shows similarities in size and general shell shape and in some details of the operculum structure (low conical shape). Nevertheless, they clearly differ by lack of the three mentioned shell features of Phreatomascogos gregoi sp. n. We considered especially the extreme campanulate operculum and the covered umbilicus of Phreatomascogos gregoi sp. n. as important apomorphic features that justify the erection of a new genus most likely within the Lithoglyphinae family. The mentioned conchological similarities between both Phreatomascogos from Coahuila and Phreatodrobia from Texas is the main reason of assigning the new genus to the family Lithoglyphinae (and not to the Cochliopidae). However, the resemblance in the shell shape could be also result of an evolutional convergence. There should be also considered the below mentioned biogeographic considerations which indicate a phyletic affinity of both genera gathering within the same family. The Edwards-Trinity-Aquifer region, that hosts all eight Phreatodrobia species, is a transboundary aquifer Zone which shares the water resources of the states of Texas and Coahuila. The Sabinas River karst region, where Phreatomascogos gregoi sp. n. occurs, belong to this zone and is hydrogeologically the southwestern extension of this huge aquifer (
Balconorbis uvaldensis Hershler & Longley, 1986
MEXICO, Coahuila state, Don Martín Basin, Sabinas River, Las Adjuntas (Rancho San Carlos): 101°11'41"W, 27°53'33"N, 354 m a.s.l. (Fig.
Holotype (Figs
Shells of Balconorbis sabinasense sp. n. and Coahuilix parrasense Czaja, Estrada-Rodríguez, Romero-Méndez, Ávila-Rodríguez, Meza-Sánchez & Covich, 2017. 12–14 B. sabinasense n. sp., holotype, UJMC 410. 15–18 Paratype 1, UJMC 411. 19–21 C. parrasense, UJMC 418, from Nazas River, Durango. 22, 23 C. parrasense, fossil specimen from Parras de la Fuente, Coahuila, holotype, UJMC-320, from
Derived from the name of Sabinas River, Coahuila, where the type locality is situated.
COAHUILA. Don Martín Basin, Sabinas River, UJMC 412, Ejido Santa María, Y. A. Sanchez-Montañez, 03/vii/2018. UJMC 413, Ejido Paso del Coyote, Cecilio Arreola Chapa, 30/xi/2018. UJMC 414, Sabinas (Agua Prieta), Y. A. Sanchez-Montañez, 08/vii/2018. UJMC 415, La Vega, Y. A. Sanchez-Montañez, 08/vii/2018.
Shell minute, less than 2 mm in diameter (width), planispiral, apertural plane not or only slightly inclined, with 3¾ or less whorls, bodywhorl keeled, with spiral lines and axial growth lines, protoconch smooth.
According to
Shell minute, planispiral, width 1.51–1.81 mm, height 0.42–0.61 mm, with 3¼–3¾ whorls; protoconch smooth to slightly pitted (Fig.
(mean ± standard deviation in parentheses; n = 11): SH 0.53 (0.07) mm, SW 1.68 (0.10) mm, AH 0.59 (0.05) mm, AW 0.49 (0.08) mm, WN 3.5 (0.19), aperture plane inclination relative to shell axis = 22°–31°. Paratypes from the type locality.
SH 0.55 mm, SW 1.58 mm, AH 0.59 mm, AW 0.58 mm, HBW 0.50 mm, WN 3½, aperture plane inclination relative to shell axis = 25°.
Similar to Phreatomascogos gregoi sp. n.
Distribution. Known from the type locality and various sites among the Sabinas River between the localities Ejido Santa María and La Vega. Within the type locality and most other sites the new species occurs sympatrically to Phreatomascogos gregoi sp. n.
Almost all the members of Cochliopidae family with planispiral shells are subterranean forms. Freshwater gastropods with similar shell characteristics can be found only in the genus Balconorbis which is monotypic with B. uvaldensis in the Edwards (Balcones Fault Zone) Aquifer in Uvalde County, Texas, United State. Our new species resembles B. uvaldensis but differs from this by having larger shells, smooth protoconch, one more whorl and a bodywhorl with one or two more or less strong keels and by much closer, compressed set of the whorls resulting in weaker suture and larger columellar peristome. The later feature is unique in the genus Balconorbis and could indicate the possible position of the new species in a new geographically isolated genus. These conchological differences confirm that the new species is morphologically diagnosable and distinct to shells of the snails from Texas. It is the first record of the genus Balconorbis in Mexico.
COAHUILA, Don Martín Basin, Sabinas River, Las Adjuntas (Rancho San Carlos), UJMC 416, 417: 101°11'41"W, 27°53'33"N, 354 m a.s.l., 2 shells. DURANGO, Leon Guzmán District, Nazas River, 1 km E of the Bridge Los Cuates, UJMC 418, 103°42'13"W, 25°27'56"N, 1.158 m a.s.l., 1 shell (Figs
See
Shell 1 from Coahuila (UJMC 416): SH 0.39 mm, SW 1.44 mm, AH 0.52 mm, AW 0.36 mm, aperture plane inclination relative to shell axis = 58°. Shell 2 from Coahuila (UJMC 417): SH 0.41 mm, SW 1.43 mm, AH 0.46 mm, AW 0.38 mm, aperture plane inclination relative to shell axis = 63°. Shell from Durango (UJMC 418): SH 0.31 mm, SW 1.21 mm, AH 0.45 mm, AW 0.32 mm, aperture plane inclination relative to shell axis = 64°.
The three empty shells from Coahuila and Durango resembles in all details the shells of C. parrasense, a sub-fossil species described recently from a dried-up stream (arroyo) near the town Molino, Parras de la Fuente, Coahuila by
Because of convergences, the description of hydrobioid snails based only on shell characters can be misleading (see discussion in
These conditions of subterranean (interstitial) habitat might also explains the special morphologic adaptations of the shell. According to the hydrodynamic model of
Also, the singular covered umbilicus and the general variable form from near planispiral to trochoid of Phreatomascogos gregoi sp. n. shells might be explained by the same hydrodynamic model of
The above described new genus and species of subterranean snails from Coahuila and the recently reported findings from Yucatán (
This investigation is part of the mega-project “Ecological restoration on the riparian vegetation of the Natural Resources Protection Area, Upper Basin of the National Irrigation District 004 Don Martín”, funded by the Global Environment Facility (GEF) and implemented by the United Nations Development Program (UNDP) and the National Commission of Natural Protected Areas (CONANP). We thank Ing. Gabriela Orozco and M.S. Juan-Fernando de la Rosa (C.I.D.T. PEÑOLES, Torreón) for the scanning electron micrographs. Many people assisted with fieldwork, we thank especially Biol. Cecilio Arreola Chapa and Cand. Biol. Yabid Alexander Sanchez-Montañez for sampling and other fieldwork. We are grateful to Cand. Biol. Richard Dale Bledsoe (UJED, Gómez Palacio, Durango) for his help with English proof.