taxonID	type	description	language	source
038487B5FFA7A37009C7E04DC1CDE849.taxon	type_taxon	Type species. Microphreatus saltillensis sp. nov., by original designation.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA7A37009C7E04DC1CDE849.taxon	diagnosis	Diagnosis. Shells very small, mostly less than 1 mm in diameter (width), with up to 2.5 tubular whorls and near-planispiral to low-trochoid in form, protoconch extends the length of a whorl (1.25 whorls), sculptured with wrinkled pits, teleoconch whorls with slightly zigzag-shaped spiral lines which cross thin, weakly, irregularly distributed collabral lines; both lines start following the transition to teleoconch, teleoconch with a few collabral ribs which varying from low riblets or varices (by M. saltillensis sp. nov.) to strong lamelliform costae (by M. coronae comb. nov.), aperture near-circular, inner lip often adnate to body whorl above, peristome flared (trumpet-like), umbilicus wide. Differential diagnosis. Shells with similar characteristics to our material were only observed in the subterranean genus Balconorbis Hershler & Longley 1986, which includes two subterranean species from United States and Mexico. Nevertheless, the both genera differ in shell morphology by a combination of morphological and structural shell wall characteristics with diagnostic importance. These differences are summarized in Table 1.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA7A37009C7E04DC1CDE849.taxon	discussion	Remarks. In addition to the different general shell shape, size and number of whorls (Figs. 4 A – H), it is mainly the protoconch and teleoconch microstructure that allows the shells of both genera to be distinguished from each other. The protoconch of shells of Microphreatus are wrinkled with deep pits and without spiral lines (Fig. 3 G, H), while in Balconorbis it is smooth to slightly pitted and the spiral lines reach almost to the apex. In addition, the strong spiral and the rounded axial lines on Balconorbis shells produce a characteristic cancellate pattern (Fig. 5 E, F). Such sculpture is not developed on teleoconch of shells of both Microphreatus species, where the collabral lines are hardly developed or, if at all, only very irregularly distributed on the teleoconch (Fig. 5 A, B, E, F). Both Microphreatus species have either well-developed costae (M. coronae, Fig. 4 C, D), or at least clearly visible low varices on the teleoconch (M. saltillensis sp. nov., Fig. 5 B, C, D). At these points the spiral lines appear interrupted and offset in their course (Figs. 3 E, F, 5 A – D). Such shell sculpture in form of costae or varices does not occur on the teleoconch of shells of both Balconorbis species. Other diagnostic difference between both genera includes the raised (or even free and uncoiled) apex by shells of Microphreatus (Fig. 4 A, C), meanwhile both Balconorbis species always have planispiral shells with a sunken apex (Fig. 4 E – G).	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA7A37009C7E04DC1CDE849.taxon	etymology	Etymology. The name is derived from Greek word micro (μικρός) = small, and phreato = groundwater environment where the snails live.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA7A37009C7E04DC1CDE849.taxon	distribution	Distribution. Disjunct, with one species living in Val Verde County, southern Texas, United States and other in Los Chorros, Coahuila, Mexico (see below).	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA4A37409C7E1D6C250E939.taxon	description	Figures 3 A – F	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA4A37409C7E1D6C250E939.taxon	materials_examined	Type locality. A groundwater fed spring (Manantial) inside the recreation park “ Los Chorros ”, Sierra de Zapalinamé, municipality of Arteaga, ca. 8 km southwest of the town of Arteaga, near the city of Saltillo, Coahuila, Mexico (25 ° 22 ′ 54.39 ′′ N, 100 ° 47 ′ 17.38 ′′ W, 1,914 m a. s. l) (Fig. 2 A). Type material. Holotype (Fig. 3 B – D), UJMC 628, from type locality, leg. Gabriel Fernando Cardoza-Martínez, 30 / xi / 2018. Paratypes, UJMC 629 - 633 b, from the same lot, 11 specimens. Material Examined. Holotype and Paratypes – Groundwater fed spring (Manantial) inside the recreation park “ Los Chorros ”, Sierra de Zapalinamé, collected by Gabriel Fernando Cardoza-Martínez, 15 July 2024, and site 2 (25 ° 22 ′ 50.01 ′′ N, 100 ° 47 ′ 19.10 ′′ W), a narrow trickle of 40 – 50 cm wide, are located approximately 150 meters downstream, collected by Ricardo Marco Ávila Hernández, 05 December 2024, both sites ca. 8 km southwest of the town of Arteaga, Coahuila, Mexico.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA4A37409C7E1D6C250E939.taxon	etymology	Etymology. The species is named for its occurrence near the city of Saltillo, Coahuila, Mexico.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA4A37409C7E1D6C250E939.taxon	diagnosis	Diagnosis. Shells very small, less than 0.8 mm in diameter (width), with up to 2.3 tubular whorls, near-planispiral to low-trochoid, protoconch extends the length of a whorl, sculptured with wrinkled pits, teleoconch whorls with slightly undulated spiral lines which cross thin, weakly, irregularly distributed collabral lines, both lines start following the transition to teleoconch, teleoconch with a few collabral ribs which varying from low riblets or varices, aperture near-circular, inner lip often adnate to body whorl, peristome flared, umbilicus wide.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA4A37409C7E1D6C250E939.taxon	description	Description. Shell minute, ranging from 0.68 mm to 0.79 mm in diameter and 0.31 mm to 0.41 mm in height, white, near planispiral or (mostly) depressed-trochoid in form (Fig. 3 D), deeply impressed sutures, the spire is mostly raised up, protoconch of 1.25 whorls, sculptured with wrinkled pits (Fig. 3 G, H); diameter of protoconch about 280 μm, diameter of nucleus about 90 μm (holotype), the body whorl prominent, teleoconch whorls with slightly zigzag-shaped spiral lines which cross thin, and irregularly distributed collabral lines (Fig. 5 A, B), both lines start following the distinct transition to teleoconch (Fig. 3 H), distance between the spiral lines in average 15 μm, lamelliform costae (like by M. coronae comb. nov.) absent, but always with about 13 – 20 faintly visible collabral riblets or varices (Figs. 3 E, F, 4 A, B, 5 C); aperture near-circular and prosocline, inner lip adnate to body whorl above, peristome slightly flared to trumpet-like, umbilicus deep and wide (Figs. 3 C, E, 4 B, D). Shell measurements (mean ± standard deviation in parentheses; n = 13): SH 0.36 (0.03) mm, SW 0.73 (0.03) mm, AH 0.30 (0.02) mm, AW 0.29 (0.03) mm, WN 2.3 (0.00), paratypes from the type locality. Measurements of Holotype. SH 0.37 mm, SW 0.74 mm, AH 0.32 mm, AW 0.31 mm, WN 2.3. Habitat. Like in many other sites with subterranean gastropods, no living individuals from the site Los Chorros could be obtained. However, the collected snails apparently died recently because the shells do not reveal any signs of external weathering. They were washed out from their subterranean habitat and deposited directly at the water outlet. The new species lives in subterranean habitat (stygobitic). The water chemistry values at site 1 were as follows: temperature = 19.8 ° C, pH = 7.00, conductivity = 1228 μS / cm, dissolved oxygen = 7.1 mg / L.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA4A37409C7E1D6C250E939.taxon	distribution	Distribution. Known from the type locality and one site in the immediate vicinity within the recreation park Los Chorros. The new species lives in subterranean habitat and appears to be endemic to the spring. Conservation assessment. The NatureServe rank calculated for Microphreatus saltillensis sp. nov. is Critically Imperiled (N 1).	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFA4A37409C7E1D6C250E939.taxon	discussion	Remarks. The new species can be distinguished from species of related subterranean genera like Balconorbis, Coahuilix or Phreatodrobia only using SEM images, as the fine shell wall and protoconch structures are not observable in light microscopic images (Fig. 3 B – D). Microphreatus saltillensis sp. nov. is distinguished from M. coronae by considerably smaller shells (SW 0.68 – 0.79 mm versus 1.04 – 1.17 mm), lack of lamelliform costae (Fig. 3 B, C), raised, but never uncoiled protoconch (Fig. 3 F – H) and significantly weaker spiral lines on the teleoconch (Fig. 4 A – D). The size of a snail is usually determined by the height of the shell, or, in the case of planispiral shells, by its width (diameter). Microphreatus saltillensis sp. nov., with a diameter of 0.73 mm (on average), is therefore probably the world’s smallest described freshwater snail, only slightly smaller than Hadziella forneri Quiñonero-Salgado, López-Soriano & Rolán, 2023 (Hydrobiidae) from Spain, which is 0.77 mm wide (Quiñonero-Salgado et al., 2023). Other sympatric snails from site 1 belong to the genera Physella, Ferrissia, Chorrobius, Pyrgulopsis, Gyraulus and Galba.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFAFA37B09C7E7FDC01DEDAC.taxon	description	Description. See Hershler & Longley, 1987, pp. 133 – 134 and Perez et al., 2025 pp. 140 – 141.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFAFA37B09C7E7FDC01DEDAC.taxon	distribution	Distribution. Endemic to springs of Val Verde County, Texas, United States.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
038487B5FFAFA37B09C7E7FDC01DEDAC.taxon	discussion	Remarks. Phreatodrobia coronae was originally assigned to Phreatodrobia due to the similar shell outline of some species of this subterranean genus (Hershler & Longley, 1987; p. 137). Recently, this species was transferred to the genus Balconorbis based on mitochondrial and nuclear data by Perez et al. (2025). However, according to the authors, the average divergence in COI between Balconorbis uvaldensis and P. coronae was 18.5 %, slightly above the divergence among genera in related subterranean groups (Perez et al., 2025, p. 140). Although Phreatodrobia coronae was reassigned to Balconorbis, the authors explicitly mention that this species does not fit “ perfectly ” in this genus and may need to be placed into a new genus. Our comparison shows that even according to morphological characteristics of the shell wall structure this species can be classified in neither the genus Balconorbis nor in Phreatodrobia and is consequently placed here in a new genus. The scanning electron microscope images of the proto- and teleoconch microsculpture of P. coronae shells from the original description by Hershler & Longley (1987, p. 135 – 136) shows similarities down to the smallest detail with shells of M. saltillensis sp. nov. described above (Figs. 3 G – I, 4 A – D, 5 A – D). These structural similarities indicate that both forms (coronae and saltillensis) belong to a same group or lineage, independent from Balconorbis and Phreatodrobia. We reassigned the material from Texas to Microphreatus as a second species of this genus.	en	Czaja, Alexander, Cardoza-Martínez, Gabriel Fernando, Becerra-López, Jorge Luis, Estrada-Rodríguez, José Luis, Alonzo-Rojo, Fernando, Ávila-Rodríguez, Verónica, Valenzuela-García, Ana Alejandra (2025): World’s smallest freshwater snail? A new genus and species of subterranean snail (Gastropoda, Cochliopidae) with extremely tiny shell from Los Chorros, Coahuila, northern Mexico. Zootaxa 5660 (3): 413-425, DOI: 10.11646/zootaxa.5660.3.7, URL: https://doi.org/10.11646/zootaxa.5660.3.7
