Idiopyrgus adamanteus, Salvador & Silva & Bichuette, 2022

Salvador, Rodrigo B., Silva, Fernanda S. & Bichuette, Maria E., 2022, Phylogenetic position of the relict South American genus Idiopyrgus Pilsbry, 1911 (Gastropoda, Truncatelloidea), with the description of two new cave species, Zoosystematics and Evolution 98 (2), pp. 365-375 : 365

Idiopyrgus adamanteus sp. nov.

Fig. 2A-H

Type material.

MZSP 158237 (holotype), LES 0027974 (14 paratypes, from type locality), LES 0027975 (3 paratypes, from type locality).

Type locality.

Brazil, Bahia state, Central municipality, Toca Bonita cave.

Distribution.

Known from four caves in Central municipality.

Etymology.

From Latin, meaning 'of diamond’; an allusion to the region in Bahia known as Chapada Diamantina, where all the caves in the species’ known distribution are located.

Diagnosis.

Elongated shell spire; narrow body whorl; more circular aperture when compared to congeners.

Description.

Shell small, truncatelloid, of translucent beige to whitish color. Protoconch bulbous and translucent, of fragile appearance (it is broken off in many specimens). Spire narrow. Shell smooth except for fine growth lines; growth lines can be more marked in some specimens, forming a light axial ribbing pattern (Fig. 2E, G ). Suture deep; subsutural cord observed in one specimen (Fig. 2E ). Whorl profile markedly convex, rounded. Whorls initially increasing regularly in size with growth, but final whorls are typically similar in size (Fig. 2A, D-G ). Aperture small in proportion to body whorl; oval to circular, with a more acuminate end towards the upper lip insertion. Peristome complete; reflexed but not thickened. Shell rimate. Operculum translucent, of same color as the shell. Soft body white.

Measurements.

holotype: 6½ whorls, H = 5.3 mm, D = 2.3 mm; mean (n = 7), 6½ whorls (min 6, max 7), H = 5.6 ± 0.39 mm, D = 2.5 ± 0.12 mm.

Genetic data.

GenBank reg. nrs: COI, ON323464; 16S, ON359913; ITS2+28S, ON324828.

Remarks.

Idiopyrgus adamanteus sp. nov. is most similar in shell shape to I. souleyetianus and I. brasiliensis , but it can be diagnosed from them by the fewer number of whorls and the much narrower body whorl, as well as a more circular aperture (Fig. 1 ). It can be distinguished from I. rudolphi by the deeper suture, more convex whorl profile and more circular aperture. It differs from the remaining congeners by its narrower shell, more elongated spire and smaller aperture (in proportion to body whorl).

Idiopyrgus adamanteus sp. nov. displays a fair amount of morphological variation in the shell, even in specimens from the same cave (Fig. 2A-D, F-H ), like what is observed in many other freshwater truncatelloids. The shell and the spire of some specimens can be shorter (Fig. 2C ) or taller and more elongated (Fig. 2D ), the body whorl can be slighter wider (Fig. 2C, H ), the shell sculpture can be more prominent (Fig. 2E, G ), and a subsutural cord can be present (Fig. 2E ).

Given its occurrence in four distinct caves of Central region (Bahia state), Idiopyrgus adamanteus sp. nov. is considered a troglophilic species rather than a strict troglobitic one. The region of Central is characterized by a dry vegetation type (Caatinga) and the caves represent good shelters for these animals, given their high-humidity microhabitats. Few collections were conducted outside the caves and, as such, this species occurrence outside subterranean habitats was not tested. Nevertheless, the lack of body pigmentation and the translucent shell of some specimens (Fig. 2A-H ) are possible troglomorphisms, i.e., morphological traits typically observed in cave-dwelling gastropods ( Christiansen 2012; Trontelj et al. 2012; Salvador et al. 2022).

The caves of Central municipality and their surroundings are impacted by deforestation caused by subsistence agriculture, mining activities, and wind energy installations in the karst landscapes (Bichuette, pers. obs.).

Figures

Figure 1. Shells of Idiopyrgus spp. A, B. I. souleyetianus Pilsbry, 1911, holotype ANSP 100534; C, D. I. pilsbryi Baker, 1914, lectotype ANSP 130700; E. I. walkeri Pilsbry, 1924, reproduced from Pilsbry (1924: p. 6, fig. 9); F, G. I. rudolphi (Hass, 1938), holotype SMF 24365; H. I. brasiliensis (Rey, 1959), reproduced from Rey (1959: p. 145, fig. 2). Scale bars: 1 mm.

Figure 2. Shells of the two new species of Idiopyrgus. A-H. Idiopyrgus adamanteus sp. nov.; A, B. Holotype MZSP 158237; C. Paratype LES 0027975; D. Paratype LES 0027975; E. LES 0027975 (from Gruta da Machadinha); F. LES 0027978 (from Toca de Candeias); G. LES 0027977 (from Toca de Candeias); H. LES 0027978 (from Toca de Candeias); I-K. Idiopyrgus minor sp. nov.; I, J. Holotype MZSP 158238; K. Paratype LES 0027980 (from Gruna do Engrunado). Scale bars: 1 mm