Tryonia seemani Frauenfeld 1863
Creators: name: Hershler, Robert
name: Liu, Hsiu-Ping
name: Landye, Jerry
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Hydrobiidae
Tryonia
Tryonia seemani

description: Tryonia seemani (Frauenfeld, 1863)
(Figs 5 O –P, 12C–E, H–I, M– O)
Hydrobia seemani Frauenfeld, 1863: 1025. Frauenfeld, 1865: 525, plate 8.
Types. Syntypes (5 dry shells), BMNH 20001099.
Type locality. N. W. Mexico, Durango.
Referred material. DURANGO. USNM 874125, unnamed spring on west side of Nombre de Dios, 23º51'1.2" N, 104º14'54" W, leg. J.J.L. et al., 7/v/1991. USNM 854937, ibid., leg. R.H. and J.J.L., 11/xii/1998. USNM 873242, unnamed spring in Amado Nervo, southwest of Villa Union, 23º50'34.2" N, 104º11'18" W, leg. J.J.L. et al., 2/xi/1971. USNM 874123, ibid., leg. J.J.L. et al., 7/v/1991. USNM 854936, ibid., leg. R.H. and J.J.L., 11/xii/ 1998.
Diagnosis. Shell medium-sized, conic or turriform, weakly sculptured; penis having two distal and sometimes one basal papillae on the inner edge.
Description (of referred material). Shell (Fig. 12 C–E) up to 4.3 mm tall, large females having 5.25–7.25 whorls, spire height 130–200% width of shell, male shells smaller than those of females. Teleoconch whorls medium to highly convex, evenly rounded with impressed sutures. Sculpture of strong growth lines, weak spiral threads rarely present. Aperture pyriform, parietal lip complete in larger shells, usually adnate, rarely slightly disjunct, umbilicus narrow or absent. Outer lip slightly orthocline or prosocline. Periostracum olive or tan.
Shell measurements (mean in parentheses): height 3.01–4.26 mm (3.52), width 1.27–1.59 mm (1.40), body whorl height 1.55–1.89 mm (1.69), body whorl width 1.24–1.52 mm (1.35), aperture height 0.85–1.03 mm (0.94), aperture width 0.72–0.93 mm (0.81), total number of whorls 6.00– 7.25 mm (6.44) (USNM 874123, n = 12).
Inner and outer sides of operculum smooth (Fig. 12 H–I). Radula (Fig. 12 M-O): dorsal edge of central radular teeth concave, basal tongue rounded, median cusps elongate, distally pointed, parallel-sided proximally, lateral cusps five–eight, basal cusps one–two (innermost larger) (Fig. 12 N). Lateral teeth having four–seven cusps on inner and five–eight cusps on outer side, length of outer wing 145–185% width of cutting edge, central cusp pointed (Fig. 12 O). Inner marginal teeth with 26–37 cusps, outer marginal teeth with 24–34 cusps. Radula data are from USNM 874123, USNM 874125.
Animal lightly pigmented. Penis (Fig. 5 O –P) having two (39 of 47 specimens from two samples) or three (5 of 47) distal papillae and sometimes a basal papilla (19 of 47) on inner edge; one specimen differed in having a single distal papilla. Distal bulb of penis expanded laterally on inner side; stylet small. Penial duct nearly straight. Penial data are from USNM 874123, USNM 874125.
Distribution and habitat. Distributed in the upper Río Mezquital drainage (Fig. 1, localities 16–18). The springs at Nombre de Dios are at the western edge of the village on the south side of Highway 45. The first collections (in 1971) of T. seemani from this area were from a spring (adjacent to the highway) that flowed south into a canal. Snails were also found in a nearby cienega (Fig. 6 Q) which discharged toward the Río Durango. When visited again in 1991 the spring adjacent to the highway was dry and the cienega had been developed for a school. However, T. seemani was found abundantly (on vegetation and detritus) in small spring runs (19°C) within the cienega. Tryonia seemani has also been collected from springs to the east of Nombre de Dios that are locally referred to as Ojitos de Amado Nervo. The first collections at this site (1971) were made at a highly degraded spring (23°C) by the highway (Fig. 6 R) where snails were found at the bases of Chara mats. By 1998 this spring had dried, but T. seemani was abundant (on aquatic vegetation and soft substrates) in other spring vents and brooks (22°C) about 50 m to the north. The only specimens that had been previously referred to this species (aside from the syntypes) were collected near the end of the 19th century from the spring that served as the domestic water source for Durango City (USNM 251826; Morrison 1945). This site was almost certainly the Ojo de Agua del Obispo (in El Parque Guadiana) (Fig. 1, locality 16) based on historical accounts (e.g., Cigarroa 1990). One of us (J.J.L.) recently (2011) visited this spring, which has been impounded and otherwise extensively modified, and did not find T. seemani, which has likely been extirpated from the site.
Remarks. The type locality of T. seemani has not been further restricted subsequent to its original description (Hershler et al. 2002a); thus it is not known if Frauenfeld was referring to Durango City or, more generally, Durango State (Thompson 2008). Hershler et al. (2002a) transferred Hydrobia seemani to Tryonia based on the glandular penial papillae and short (female) sperm tube that was observed in resuscitated specimens (USNM 251826) whose shells closely conformed to the syntypes of this species. We have further studied these specimens and determined that they also have the diagnostic male reproductive anatomy of Tryonia. Hershler et al.’s (2002a, fig. 2) illustration of the penis of these snails is incorrect as the basal papilla is actually positioned on the inner (not outer) edge.
The Amado Nervo and Nombre de Dios snails are assigned to T. seemani based on the close similarity between their shells and the high spired, convex whorled syntypes of this species (Hershler et al. 2002a, fig. 1B). These two populations, which are separated by about 6.0 km, were delineated as a poorly supported (46% posterior probability) clade in the Bayesian analysis (Fig. 2). They differ in shell size (3.52 vs. 2.39 mm shell height, t-test, t = 8.118, df = 18.0, P <0.01, n = 8 for Nombre de Dios sample) and number of shell whorls relative to shell height (1.84 vs. 2.34, t-test, t = -9.275, df = 11.0, P <0.01) (Fig. 12 D–F), and are further differentiated in that specimens from Nombre de Dios consistently have a basal penial papilla (all 17 specimens) while those from Adamo Nervo rarely do (2 of 30 specimens). However, our COI data suggests limited (0.8%) genetic divergence between these populations, thus we treat them as conspecific.
description: Published as part of Hershler, Robert, Liu, Hsiu-Ping & Landye, Jerry, 2011, New species and records of springsnails (Caenogastropoda: Cochliopidae: Tryonia) from the Chihuahuan Desert (Mexico and United States), an imperiled biodiversity hotspot, pp. 1-32 in Zootaxa 3001 on pages 27-29, DOI: 10.5281/zenodo.278442