Vitropyrgus 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

Genus Vitropyrgus Perez & Guerrero, 2023 gen. nov.

Figs 5 , 6

Type species.

Vitropyrgus lillianae gen. et sp. nov.

Diagnosis.

Minute shell with spiral and collabral sculpture on teleoconch that extends to sutures. Embryonic whorl distinctively sculptured with wrinkles giving a malleated appearance. Aperture ovate to round, with slightly reflected lip near umbilicus. Umbilicus open. Animal eyeless and unpigmented. Penis attached behind right eye position, simple in glandular structure. The single known species of Vitropyrgus is a quarter of the size of related epigean taxa and is adapted to a subterranean environment (e.g., lacking pigmentation, eyes, and ctenidia). Simple penial morphology lacking the papillae or apocrine glands that define other members of Cochliopidae . Finally, the shell has a distinctive clear and glassy appearance, lacking the tan color of Tryonia or Stygopyrgus Hershler & Longley, 1986 or the usual translucency of Phreatodrobia .

Taxonomic remarks.

The most recent review of Cochliopidae ( Hershler and Thompson 1992) divided the family into three subfamilies, Cochliopinae Tryon, 1966, Littoridininae Thiele, 1928, and Semisalsinae Giusti & Pezzoli, 1980 largely distinguished by glandular features of the male reproductive anatomy, including “Tribe” Heleobia Thompson, 1968 ( Hershler and Thompson 1992; Liu et al. 2001) diagnosed by apocrine penial glands. Cochliopinae (e.g. Cochliopina W. Stimpson, 1865) is diagnosed by a simple, non-glandular penis with a long filament distinct from the wrinkled or folded base and Littoridininae (including Stygopyrgus , Pyrgophorus , Mexipyrgus , and Tryonia ) is characterized by a long sperm duct and often with numerous glandular papillae. A subsequent molecular phylogenetic analysis broadly supported these groupings ( Liu et al. 2001).

We do not attempt to place this genus among the subfamilies of Cochliopidae . The COI phylogeny has limited resolution at this level, we have limited sampling in LSU for placement among subfamilies. The COI tree places Vitropyrgus close (with no support) to a clade that included Heleobia ( Semisalsinae ) and Onobops ( Littoridinae ). Members of Semisalsinae are diagnosed by penial papillae or apocrine glands ( Liu et al. 2001), which Vitropyrgus lacks. Onobops is one of several cochliopid genera that have a simple penis with no papillae or apocrine glands, resembling Vitropyrgus . Onobops are epigean, brackish water species from North America. The subfamily placement of this genus is best defined as uncertain along with many other genera in Cochliopidae .

Vitropyrgus is proposed as a new genus with the following rationale. First, it was found by COI and LSU phylogenies sister to epigean taxa. In the COI phylogeny, Vitropyrgus is most closely related to members of the Heleobia and Onobops . Divergence in COI between Vitropyrgus and other members of that clade averaged 16.0% with a range from 15.5-16.6. Intergeneric comparisons in our dataset averaged 16.54% with a range from 5.19-25.37. This places the level of divergence between Vitropyrgus and its closest known relatives within the range of intergeneric divergence and just under the average for the Texas genera. In other groups of subterranean hydrobioids the range of 14.5-16.7% has been used to justify genus level distinction ( Delicado et al. 2019; Delicado and Gürlek 2021).

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.