Spinopyrgus luismaedai Czaja, Covich, Neubauer & Estrada-Rodríguez, 2022

Czaja, Alexander, Covich, Alan P., Neubauer, Thomas A., Estrada-Rodríguez, José Luis, Ávila-Rodríguez, Verónica & Mata, Jorge Sáenz, 2022, A new freshwater snail genus and species (Gastropoda: Caenogastropoda, Cochliopidae) with extremely spinous shells from sub-recent spring deposits in northeastern Mexico, Zootaxa 5169 (5), pp. 472-480 : 474-476

Spinopyrgus luismaedai Czaja, Covich, Neubauer & Estrada-Rodríguez n. gen. et n. sp.

( Figures 2A to 3P)

ZooBank registration number: urn:lsid:zoobank.org:act:385187F6-986B-4200-84D1-91147F22F4D1

Etymology. The new species is named in honor of Dr. Luis Maeda Villalobos, Torreón, Coahuila, who was the first collector of fossil snails at Viesca.

Holotype. Specimen UJMC-250 ( Fig. 2A, B ).

Type locality. Superficial sediments in the desiccated Juan Guerra spring, ca. 1 km south of Viesca, Coahuila, Mexico. Collected by Alexander Czaja and José Luis Estrada-Rodríguez, 2014 ( Figure 1 ).

Type material. Holotype ( Fig. 2A, B ), UJMC-250 from Juan Guerra spring, Viesca, 25° 19’ 17’’N, 102° 49’ 08’’W, paratypes ( Figs. 2C–F ), UJMC 251 , UJMC 252 , UJMC 252 a . Paratypes 1, 2 and 3 from the same lot as the holotype.

Type horizon. Holocene (sub-fossil).

Studied material. 154 specimens from the type locality ( UJMC 250-252 b, 254) , 45 specimens from El Molino spring ( UJMC 253-253 c) and 50 specimens from Hacienda de Hornos y Carranza spring ( UJMC 257-257 c) .

Occurrence. Endemic to Juan Guerra, Hacienda de Hornos y Carranza and El Molino springs near Viesca, Coahuila, Mexico.

Diagnosis. Shell medium-sized, usually light brown or (when blanched) white, narrow-conic, variably umbilicate to imperforate. Aperture round polygonal, inner lip adnate. Teleoconch whorls having one to three distinct keels sculptured with broad, strong, conical spines.

Description. Shell medium-sized, thickened, imperforate, and conical, up to 7.25 whorls, the holotype has 6.25 whorls, first two rounded. The apex is acute and inclined, protoconch consisting of about one whorl, smooth or slightly wrinkled, measuring 160–180 µm in diameter. A shoulder frequently develops on early teleoconch whorls. The slightly corrugate nucleus is narrow and immersed and has 40–50 μm in diameter. Protoconch-teleoconch boundary is clearly discernable, characterized by the onset of fine, axial growth lines, which are prosocline on first whorls and later become almost orthocline. Teleoconch whorls have fine or often more pronounced irregular axial ribs ( Fig. 2J , 3O ), as well as two to three spiral carinae. Because of the strong carinae the whorls appear more angular than rounded ( Fig. 2A–H , 3L ). Along the central carina, many axial ribs extend into strong spines on the periphery. The spines are regularly spaced and always in the middle part of the whorl. The last three or four whorls are geniculate, angled at location of carina. Body whorl large, almost always having a second carina with spines on the lower side, sometimes with a third carina ( Fig. 2E, F ). Whorls mostly with very pointed, shovel-shaped spines, with up to 30 spines on the body whorls, spines very pointed. The spines like all other shell ornamentations are part of the calcareous shell material. Suture slightly impressed. Many shells conserve still their thin light-brown periostracal layer ( Figs. 2C–J ). Aperture polygonal, mostly pentagonal in shape ( Figs. 2A, E, G ), slightly longer than wide. Parietal lip adnate, the basal and outer lip rounded and thin. Opercula were not preserved.

Shell measurements (mean ± standard deviation in parentheses; n = 20). SH 4.64 (0.46) mm, SW 2.19 (0.31) mm, WN 6.05 (0.49) whorls (shells from Juan Guerra spring).

Measurements of Holotype. SH 4.91 mm, SW 2.72 mm, AH 1.89 mm, AW 1.83 mm, AH/SH 0.39, WN 6.25 whorls.

Remarks. The prominent spine ornamentations of S. luismaedai with extremely long and almost “marinelike” spines are not seen in any other North American gastropod species. All spines are built completely of shell material and are not made of a combination of shell material and periostracal projections, like in some other spiny Pyrgophorus Ancey (Cochliopidae) or Potamopyrgus Stimpson (Tateidae) species. The variability of the shell ornamentations is remarkable especially regarding the number and form of the spines ( Fig. 2C–K ). Most of the shells are turriform with 5–7 elongated whorls ( Fig. 2A–H ), but there are also in all springs a sub-population with a more rounded general form and less than 5 whorls. This variability could be an indication of different ecophenotypes within the S. luismaedai populations.

Figures

FIGURE 1. Study area showing the locations of the Viesca springs. The scale bar refers to the map with the springs marked. The topography is illustrated using HillShade in ArcGIS.

FIGURE 2. Spinopyrgus luismaedai n. gen. et n. sp. (A–K). A–B. Holotype (UJMC-250) from Juan Guerra spring. C. Paratype 1 (UJMC-251) from Juan Guerra spring. D. Paratype 2 (UJMC-252) from Juan Guerra spring. E, F. Paratype 3 (UJMC-252a) from Juan Guerra spring, specimen with three keels. G. Specimen (UJMC-253) from El Molino spring. H. Specimen (UJMC- 254) from Juan Guerra spring. I. Specimen (UJMC-253) from El Molino spring, protoconch view. J. Paratype 3 (UJMC-251), details of the carina with spines. K. Specimen (UJMC-253b) from El Molino spring, details of the carina with shovel-shaped spines.

FIGURE 3. SEM images of Spinopyrgus luismaedai n. gen. et n. sp. (L–P). L. Specimen (UJMC-255) from El Molino spring with strong spines. M. Specimen (UJMC-255) apical view. N. Specimen (UJMC-256), protoconch. O. Specimen (UJMC-255), details of the strong axial elements of the body whorl. P. Specimen (UJMC-256) from Juan Guerra spring, protoconch. Q-T. Pyrgophorus parvulus (Guilding) from Río Sabinas, Coahuila, Mexico (from Czaja et al. 2022, Fig. 5A). Q, R. Specimen (UJMC 460a) from Río Sabinas from both sides. S. Same specimen with details of the spiral elements of the body whorl. T. Same specimen (UJMC 460a), protoconch.