Vitropyrgus lillianae Perez & Guerrero, 2023

Perez, Kathryn E., Guerrero, Yamileth, Castaneda, Roel, Diaz, Peter H., Gibson, Randy, Schwartz, Benjamin & Hutchins, Benjamin T., 2023, Two new phreatic snails (Mollusca, Caenogastropoda, Cochliopidae) from the Edwards and Edwards-Trinity aquifers, Texas, Subterranean Biology 47, pp. 1-27 : 1

Vitropyrgus lillianae Perez & Guerrero, 2023 sp. nov.

Figs 5 , 6

Stygopyrgus bartonensis , Hutchins 2018, suppl. material 1: table S1.

Stygopyrgus bartonensis , Hutchins et al. 2021, suppl. material 1: table S2.

Type locality.

USA, Texas. Comal County, New Braunfels, Comal Spring Upwelling #7, (29.7135, -98.1370).

Material examined.

All sites are in Texas, USA. Holotype - Comal County, Landa Park , New Braunfels , Comal Spring Upwelling #7, (29.7135, -98.1370), drift net, collected by Randy Gibson, 2 May 2019 (ANSP 494654). Paratypes - Comal County, Landa Park, New Braunfels, Comal Spring Upwelling #7, (29.7135, -98.1370), drift net, collected by Randy Gibson, 1-5 June 2018 (ANSP 494656) .

Additional material examined.

- Kerr County, Fessenden Spring , near Heart of the Hills Fisheries Science Center (30.1670, -99.3427), drift net, collected by K. E Perez, D. Deshommes, N. Loveland, 4-6 November 2020 (ABC 005622) .

Diagnosis.

Minute shell with glassy appearance, with distinctive spiral and collabral sculpture on teleoconch that extends to sutures. Vitropyrgus lillianae differs from similar species in the region by shell shape, sculpture, or shell color. Stygopyrgus bartonensis has a taller, more columnar, and less heavily sculptured shell. The shell of S. bartonensis also has a pale brown tint in fresh shells that is not present in V. lillianae . The animals most easily confused with V. lillianae are very juvenile individuals of Pyrgophorus spinosus (Call & Pilsbry, 1886). While their sculpture can appear quite similar, juvenile P. spinosus are much larger, have a white base color and the aperture forms an oval, completely appressed to the body whorl. Pyrgulopsis spinosus shells have a more steeply tapering spire than V. lillianae . Dissection and comparison of penial anatomy will readily distinguish V. lillianae due to its simple structure with no papillae or apocrine glands.

Description.

Shell very small, clear, glassy, heavily sculptured, ovate-conic with rounded whorl outlines (Fig. 5A-D ). Average shell measurements for adults (n = 20): shell height = 0.737 mm (SD = 0.25), shell width = 0.470 mm (SD = 0.17), aperture height = 0.333 mm (SD = 0.11), aperture width = 0.268 mm (SD = 0.09), number of whorls = 4.5 (SD = 0.20).

First whorl of protoconch slightly elevated, separated from subsequent whorls (Fig. 5E, F ). Protoconch surface heavily sculptured by wrinkles that form irregularly shaped shallow depressions or pits. Teleoconch sculpture includes finely spaced collabral ribs dissected by spiral lines (Fig. 5F, G ). Ribs slightly more elevated, spaced 20-23 µm apart. Aperture ovate, slightly pulled away from body whorl, only lightly touching body whorl at parietal corner. Lip reflected on basal and umbilical portions in larger individuals. Outer lip straight, simple, slightly tilted forward (prosocline). Umbilicus open. Operculum clear, extremely thin, pliable, fragile (Fig. 5H ). Shape elongate ellipsoidal, nucleus submarginal, spiral weakly convex. Growth lines not distinct or frilled.

Unpigmented body visible through shell. Snout nontapered, about as long as wide, with strong distal lobation. Foot short, anterior portion rounded, anterior edge indented, without lateral wings. Cephalic tentacles tapered, rounded, unpigmented, with no visible cilia, about 5 times as long as wide. Mantle tissue unpigmented. No visible eyes and no visible pigment at base of eyestalks. No ctenidium observed, osphradium rounded.

Intestine uncoiled, mostly filled with rounded fecal pellets, rectum exiting in pallial cavity, near mantle edge on right side of head. Esophagus entering stomach below, smaller posterior chamber with large digestive gland aperture and larger anterior chamber. Stomach speckled with dark flecks of pigment. Caecum not observed.

Penis large relative to body size tapering, attached well behind right eye, with an expanded, muscular base, narrow body segment, tapering to a distal tip (Figs 5I, J ). Penis base with moderate folding along inner curvature. Distal portion tapered, inner and outer curves with aglandular curving lobes nearly opposite each other, giving a blunt, asymmetrical “arrowhead” shape to distal portion of penis. Neither apocrine glands or papillae present on examined individuals. Cilia not observed on distal penis.

Central radular tooth with indented dorsal edge (Fig. 6A ); lateral cusps 4 on each side; central cusp ~1/3 longer than adjacent cusps, pointed but tapering at the end and at the base, wider in the middle, singular basal cusps pointed, with small buttress, paddle shaped, not needle-like, basal process triangular in shape; deep basal socket. Lateral tooth rectangular, narrowing slightly upon reaching the outer wing; outer wing tapering; central cusp longer than lateral cusps, 5-6 cusps outer and 5 cusps inner direction, decreasing in size distally. Inner marginal teeth with broad outer wing with basal notch, 17-19 cusps, mostly similar in length except two outermost cusps shorter, triangular, wide at base. Outer marginal teeth broad and curved at end, with 14-16 cusps. Cusps along inner edge longer; tooth face tapering to outer wing which then broadens again at base (Fig. 6B, C ).

Etymology.

We use the generic name " Vitropyrgus " reflecting the glassy appearance of the shell of this phreatic snail compared to related groups. The specific epithet " Vitropyrgus lillianae " is in honor of Dr. Lillian E. Perez, the first author’s mother. We propose the common name "glass cavesnail".

Ecology.

This new snail species is found among other phreatic snail fauna in Comal Springs including: Phreatodrobia nugax (Pilsbry & Ferriss, 1906), Phreatodrobia plana Hershler & Longley, 1986, Phreatodrobia spica K. E. Perez & Alvear, 2020, and Phreatodrobia rotunda Hershler & Longley, 1986. Other members of this unique subterranean fauna include the federally endangered amphipod Stygobromus pecki (Holsinger, 1967), the federally endangered dryopid beetle Stygoparnus comalensis Barr & Spangler, 1992, an undescribed stygobiontic salamander, and many other invertebrates ( Hutchins et al. 2021). Federally endangered epigean fauna at Comal Springs include the riffle beetle, Heterelmis comalensis Bosse, Tuff, & Brown, 1988, fountain darter, Etheostoma fonticola (Jordan & Gilbert, 1886), and Comal Springs salamander, Eurycea neotenes Bishop & Wright, 1937.

Habitat.

This species is known from two localities in the karstic Edwards and Edwards-Trinity Aquifers, separated by ~125 km. Comal Springs is the largest spring in Texas (mean annual discharge = 8.4 m3/s, ( USGS 2023)) and discharges water from the deep confined portion of the regional San Antonio segment of the Edwards Aquifer. The spring is a complex of openings discharging on and along a normal fault that divides the deep confined and recharge zones of the Edwards Aquifer, and the springs integrate a mix of species found in one or both aquifer zones.

Fessenden Spring on Johnson Creek is a smaller spring that is part of the large regional Edwards-Trinity Aquifer system. Fessenden Spring discharges from the base of the Edwards Limestone in the central Texas Hill Country and is one of many Edwards-Trinity springs that support baseflows in the headwater reaches of the Guadalupe River. Across much of the southeastern portion of this aquifer, springs discharge into streams and rivers in the contributing zone for the Edwards Aquifer. The Edwards-Trinity system is hydrologically connected to the Edwards Aquifer along the Balcones Fault zone through both groundwater and surface-water linkages. The Guadalupe River is the only river in the contributing zone to not consistently lose much or all its flow to the Edwards Aquifer as it crosses the aquifer recharge zone ( Ockerman and Slattery 2008; Wehmeyer et al. 2013). Instead, it consistently gains discharge via Comal Spring, Hueco Spring, and several other springs discharging from both the Edwards and Edwards-Trinity aquifers.

In the boundary zone between the two aquifer systems, movement of organisms across blurry hydrologic boundaries between the aquifers is possible. Additionally, there is increasing evidence that the hyporheic zone along river corridors can provide important habitat and connectivity for a variety of Texas groundwater taxa, including snails ( Hutchins et al. 2020; Sparks 2023). Because the Edwards Limestone is continuously exposed across the upper and middle Guadalupe River watershed between Fessenden and Comal Springs, it is likely that Vitropyrgus lillianae gen. et sp. nov. is more widespread than the localities reported here. More occurrences will likely be discovered once the species is characterized, and additional samples are collected across this watershed. However, given the prevalence of restricted range size in most (though not all) Texas groundwater snails ( Alvear et al. 2020a), it is unlikely that the range for Vitropyrgus lillianae gen. et sp. nov. will be expanded considerably. With only two populations currently known, the species is classified as critically imperiled (G1S1) using NatureServe methodology and considering distribution data only.

Taxonomic remarks.

The species superficially resembles Stygopyrgus bartonensis in overall shell form and sculpture and was initially identified as that species (e.g. Hutchins 2018, suppl. material 1: table S1, identification by R. Hershler, and Hutchins et al. 2021, suppl. material 1: table S2). Here we examine the relationship with both COI and LSU data of V. lillianae to several populations of S. bartonensis , including the type locality. In both analyses, while it is not certain which members of the Cochliopidae V. lillianae are closely related to, this species is not supported as closely related to S. bartonensis.

Figures

Figure 5. Shells and anatomical features of Vitropyrgus lillianae gen. et sp. nov. All localities in Texas A-C holotype, Comal Springs, Comal County, ANSP 494654 D shell frontal view of individual from Fessenden Springs, Kerr County, ABC 005622 E SEM of embryonic whorls to detail sculpture F SEM of rear shell and sculpture G SEM of teleoconch sculpture H SEM of operculum, outer view I penis, ventral view J penis, dorsal view. The yellow coloration in I and J is caused by immersion in Bouin's solution, the tissues are white, unpigmented in life.

Figure 6. SEM of Vitropyrgus lillianae gen. et sp. nov. radula A view of central radula teeth B radula ribbon showing details of inner and outer marginals C outer marginal teeth.