Texapyrgus diaboli ( Pilsbry & Ferris, 1906 ), 2025

Texapyrgus diaboli ( Pilsbry & Ferris, 1906) comb. nov.

Figs 4 D, E View Figure 4 , 5 C, G View Figure 5

Paludestrina diaboli Pilsbry & Ferris, 1906 View in CoL , pp. 170, fig. 36.

Texapyrgus longleyi Thompson & Hershler, 1991, pp. 680–682 View in CoL .

Tryonia diaboli, Diaz et al. 2020, pp. 18–24 View in CoL .

Types.

Lectotype ANSP 91726 About ANSP .

Type locality.

Spring on east side of Devil’s [sic] River in canyon just downflow from Slaughter bend (Indian Springs Canyon Springs), Amistad National Recreation Area, 32 km N of Del Rio, Val Verde County, TX, 29.6582, - 100.91765.

Additional material examined.

– All sites are in Texas, USA. Val Verde County • Finegan 105, Devils River (29.9048, - 101.0111), P. Diaz ( ABC -000882 ) GoogleMaps ; • Dolan Drift # 383 (29.8858, - 100.9933), 1 August 2016, P. Diaz ( USNM 1571310 About USNM ) GoogleMaps ; • San Felipe Creek . SW 3 - HZ 1, (29.36887, - 100.88388), 6 December 2020, B. Schwartz ( ABC -000879 ) GoogleMaps ; • Lake Amistad National Recreation Area, Slaughter Bend, small spring 25 m W of Indian Springs (29.66385, - 100.9275), 12 / 6 / 2020, K. E. Perez, C. Ortega, R. Chastain ( ABC -000878 ) GoogleMaps ; • Lake Amistad National Recreation Area: Indian Springs Canyon Springs (29.6582, - 100.91765), K. E. Perez, C. Ortega, R. Chastain (no specimens remaining) GoogleMaps ; • Snake Spring (29.896319, - 100.981214), B. Schwartz ( ABC -000883 ) GoogleMaps ; • Blue Hole, Finegan Springs, Devils River (29.8938, - 100.99456), B. Schwartz ( USNM 1571309 About USNM ) GoogleMaps ; • Indian Springs (29.66383, - 100.9275), 6 December 2020 GoogleMaps , Big Satan Canyon (29.66349, - 100.95492), 8 December 2020, B. Schwartz ( ABC -000876 ) GoogleMaps ; • Big Satan Canyon Spring (29.6635, - 100.95452), 8 December 2020, B. Schwartz ( ABC -000880 ) GoogleMaps ; • Boiling Trough Spring (29.6402, - 100.92647), J. Gordon, M. Turner, R. Hoffman ( ABC -000917 ) GoogleMaps .

Description.

Slender, elongate shell comprised of 4 ½ - 5 ½ convex whorls. Sutures deeply impressed. Average size of 1.6 mm in height, and 0.82 mm in diameter. Protoconch strongly wrinkled followed by variable teleoconch sculpture with some individuals smooth and others heavily striated. Aperture ovate, measuring an average of 0.50 mm in height, and 0.40 mm in width. Umbilicus small. Peristome thin, and slightly reflected in adults ( Thompson and Hershler 1991).

Taxonomic remarks.

Tryonia diaboli (originally Paludestrina diaboli ) was described from drift debris of the Devils River, “ about four miles from its mouth ”, and from “ the Rio San Felipe near Del Rio ”, now called San Felipe Springs. The habitat was unknown, as the types were dry, bleached shells deposited by flowing water. This region has a rich freshwater fauna of both surface and aquifer snails; however, it was uncertain from which habitat this species originated. Tryonia diaboli was described from shell anatomy, not internal morphology. The shell is described as small, 1.3 mm length, 0.62 mm diameter, very slender, and turrite (tower shaped), with 4.5 very convex whorls with deep sutures and a smooth surface ( Pilsbry and Ferriss 1906). The description and illustration ( Pilsbry and Ferriss 1906, pp. 170, fig. 36) depict a smooth shell. However, scanning electron microscope images of a lectotype (Fig. 4 D View Figure 4 , Academy of Natural Sciences of Philadelphia, ANSP 91726), which appears to be the shell illustrated in the original description, show a crosshatched pattern of longitudinal and spiral sculpture, similar to the sculpture of Texapyrgus longleyi .

Texapyrgus longleyi Thompson & Hershler, 1991 was collected from a spring on the Devils River just downstream from Slaughter Bend ( USNM 860551). The species was collected using a net over a spring opening. That habitat and the small size and unpigmented body indicated that the species is subterranean. The shell of Te. longleyi was 1.4–1.8 mm, thin and translucent with prominent spiral lines, crossed by strong longitudinal striae. The shell was described as having deep sutures, small umbilicus, aperture lip complete and touching body whorl at the top. The name includes the word “ pyrgus ” indicating the turrite or tower shape of the shell. The description of Te. longleyi is more extensive but closely resembles in many features the description and type of T. diaboli .

Due to the obscurity of the original description, it appears likely that Thompson and Hershler were unaware of T. diaboli . They do not mention T. diaboli , also from the Devils River, in their description of Te. longleyi . The original description, and a mention in a list of the type specimens in the Academy of Natural Sciences of Philadelphia are the only mention of T. diaboli in the scientific literature for more than 100 years. To further support our supposition that Hershler was unaware of T. diaboli , in a review of all species of Tryonia of North America ( Hershler 2001), Hershler does not mention T. diaboli . The species was not mentioned again in the scientific literature until it was included in a list of North American freshwater snails ( Johnson et al. 2013) and was reported in both above and below ground habitats in the Devils River ( Diaz et al. 2020). Since the “ rediscovery ” of this species name, the generic assignment of T. diaboli has not been assessed. Due to the close geographical proximity of their collection localities and close similarities of shell features, we questioned whether T. diaboli and Te. longleyi are distinct species. We conducted DNA sequencing of individuals with both “ morphological forms ” i. e. smooth vs highly sculptured. In addition, new sequences were included in an alignment with Tryonia and species from across the Cochliopidae to test the hypothesis that T. diaboli is a member of Tryonia or, if not, to determine the best generic placement.

We found that snails closely resembling the type material and descriptions of T. diaboli from springs of the Devils River are not closely related to members of Tryonia (Figs 2 View Figure 2 , 3 View Figure 3 ), meriting reassignment to a different genus. Further we find that snails resembling the type material of T. diaboli and Te. longleyi from springs of the Devils River and San Felipe springs form a monophyletic group. The snails identified as each of these species, based on shell morphology, are not reciprocally monophyletic (Figs 2 View Figure 2 , 3 View Figure 3 ). There is some divergence (9.8 %) between the populations found in springs near the Devils River and those sampled from San Felipe Springs. This could be an artifact of sequencing a limited number of individuals and the geographical gap in samples between these populations. There are some morphological differences to support further distinguishing those populations. We have considered whether populations in the Devils River and San Felipe drainages should be considered as distinct species, and while the data do not preclude the possibility, we take the more conservative approach of preserving these populations as a single species, acknowledging that additional evidence may call for further revision in the future. The average intraspecific divergence in COI in this clade is 4.6 %, within the Devils River springs is 0.6 % and within the San Felipe Springs 1.0 %.

From these lines of evidence (monophyly in both nuclear and mitochondrial sequence data and similar morphologies), we conclude that T. diaboli and Te. longleyi are synonymous and cannot remain assigned to Tryonia . The original genus Paludestrina d’Orbigny, 1840 is unavailable ( ICZN 2008). That being the case, it would be most appropriate to refer to this species as Texapyrgus diaboli ( Pilsbry & Ferris, 1906) with Texapyrgus longleyi a junior synonym.

Ecology and habitat.

The springs along the Devils River where we collected Texapyrgus diaboli , are all from the karstic Edwards-Trinity Aquifer (Georgetown Limestone) and form most of the flow for the Devils River ( Toll et al. 2017; Texas Water Development Board 2018). The Devils River, a groundwater-dependent river, is fed by numerous springs and drains a large portion of the southwestern Edwards Plateau to the Rio Grande River. One population of Texapyrgus diaboli was found in San Felipe Springs, which are among the largest in Texas with an average discharge of 3473 L / s ( Hutchison 2021). The springs discharge from Cretaceous Salmon Peak Limestone ( Barnes et al. 1992). Texapyrgus diaboli was found in drift net and hyporheic samples with water chemistry values ranging from 15.06–23.28 ° C, pH 6.49–7.4, conductivity of 366.3–608.8 μS / cm, and dissolved oxygen of 4.33–8.47 mg / L.

The springs and hyporheic zone of the Devils River and San Felipe Springs watershed support high invertebrate diversity, especially stygobiotic taxa. The groundwater obligate taxa that have been documented at the Devils River Springs of Blue Hole and Finegan Springs are: Artesia subterranea Holsinger, 1980 , Bicornucandona fineganensis Külköylüoğlu, Gibson, Diaz & Colin, 2011 , Cirolanides texensis Benedict, 1896 , Hobbsinella edwardensis Camacho, Hutchins, Schwartz, Dorda, Casado & Rey, 2017 , Ingolfiella sp. , Lirceolus bisetus (Steeves, 1968) , Parabogidiella americana Holsinger, 1980 , Paraholsingerius smaragdinus (Holsinger, 1992) , Paramexiweckelia ruffoi Holsinger, 1996 , Phreatodrobia coronae Hershler, 1987 , Phreatodrobia spica Perez & Alvear, 2020 , Seborgia hershleri Holsinger, 1982 , Speocirolana hardeni Bowman, 1992 , Stygobromus hadenoecus (Holsinger, 1966) , Texanobathynella sp. , Texapyrgus longleyi Thompson & Hershler, 1991 , Microcerberidae sp. (probably Texicerberus schotteae Hutchins & Schwartz, 2021 , but unconfirmed), and Typhloelmis finegan Barr, 2015 . Other molluscs present included Physidae , Sphaeridae , Planorbidae , and Cochliopina riograndensis .

The groundwater obligate taxa that have been documented at San Felipe Springs are: Artesia subterranea Holsinger, 1980 , Balconorbis uvaldensis Hershler & Longley, 1986 , Cirolanides texensis Benedict, 1896 , Lirceolus sp. , Mexistenasellus coahuila Cole & Minckley, 1972 , Parabogidiella americana Holsinger, 1980 , Paramexiweckelia ruffoi Holsinger, 1996 , Phreatodrobia coronae Hershler, 1987 , Psychopomporus felipi Jean, Telles & Miller, 2012 , Seborgia hershleri Holsinger, 1982 , Speocirolana hardeni Bowman, 1992 , Stygobromus sp. , Tethysbaena texana (Maguire, 1965) , and Typhloelmis sanfelipe Barr, 2015 .