Streptartemon molaris, Simone, Luiz Ricardo L. & Casati, Rafael, 2013

Simone, Luiz Ricardo L. & Casati, Rafael, 2013, New land mollusk fauna from Serra da Capivara, Piauí, Brazil, with a new genus and five new species (Gastropoda: Orthalicoidea, Streptaxidae, Subulinidae), Zootaxa 3683 (2), pp. 145-158 : 154-156

Streptartemon molaris new species

( Figs. 43–48 )

Types. Holotype MZSP 112451 ( Figs. 42–45 ). Paratypes MZSP 111840, 1 shell (sta. P2), MZSP 111841, 4 shells (sta. P4), MZSP 111843, 1 shell (sta. P2) ( Figs. 46–47 ), MZSP 112366, 1 young shell ( Fig. 48 ), MZSP 112367, 2 shells, MZSP 112371, 1 shell, MZSP 112376, 1 shell, USNM, 1 shell; MNRJ, 1 shell. All from type locality.

Type locality. BRAZIL. Piauí; Serra da Capivara ; Coronel José Dias municipality, close to Sítio do Mocó town, Cave Toca de Cima dos Pilão, 8°51’47.10”S 42°33’26.96”W (R. Casati col, 2012).

Diagnosis. Shell with height ~67% of width. Growth axis deviation of ~30%. Peristome possessing large teeth, being parietalis tooth largest and L-shaped, basalis large and as large as spiralis, located ~1/8 whorl posterior to peristome.

Description. Shell of about 9 mm. Color pure white. Periostracum not preserved. Outline broadly discoid; height ~67% of width. Protoconch of 2 whorls, opaque, flattened, almost planispiral, suture shallow; smooth ( Fig. 43 ); occupying ~6% of shell superior area (of ~1.5 mm); border protoconch-teleoconch inconspicuous, orthocline. Spire dome-shaped, of ~4 rounded whorls, low; angle ~135° ( Figs. 44 , 46 ); suture shallow, but well-marked. Sculpture wanting, shining smooth, growth lines hardly visible. Uniform growth of whorls from apex to penultimate whorl; body whorl gradually deviating to right ~30° from remaining growth axis ( Figs. 44 , 46 ), occupying ~88% of shell height and ~19% of superior shell view ( Fig. 43 ). Penultimate whorl located double as close to suture as its middle portion (opposite to aperture) ( Figs. 44 , 46 ). Peristome deflected outwards, expanding ~20% width of preceding whorl; aperture prosocline, ~40° in relation to shell growth axis. Aperture semi-circular, occupying ~25% of shell width and ~40% of width ( Figs. 44–47 ). Peristome possessing 3 large, stubby teeth ( Figs. 45 , 47 ); parietalis tooth L-shaped (concavity right), located in middle of superior half of callus, occluding ~20% of aperture (in frontal view), anterior end as base of “L”, disposed parallel to aperture, with ~half of remaining tooth length disposed perpendicularly to aperture, and ~4 times longer than wide, edges thicker than base, length ~1/8 whorl; basalis tooth occluding ~10% of aperture, located in middle region of inferior portion of outer lip, disposed parallel to peristome as a rectangular thickness of it, with ~half peristome width, and duplicating peristome width; spiralis tooth similar-shaped to basalis tooth, but with ~double its width, located ~1/8 whorl posterior to adjacent peristome edge, disposed somewhat obliquely to peristome. Outer lip rounded and bluntly angled in periphery; inner lip highly concave, parietal region occupying ~4/5 of inner lip, weakly convex, inferior region (remaining 1/ 5) weakly concave. Callus thick, planar, simple, located at base of parietalis ( Figs. 45 , 47 ). Umbilicus opened, narrow, slightly occluded by inner lip ( Fig. 42 ). Young specimen ( Fig. 48 ) simply discoid, periphery wounded, aperture semilunar.

Measurements (width and height in mm). Holotype ( Figs. 42–45 ): 8.7 by 5.1; paratype MZSP 111843 ( Figs. 46–47 ): 7.6 by 5.0.

Distribution. Only known from type locality.

Habitat. Caatinga semi-dry environment; collected inside caves.

Material examined. Types. Non-type material from type locality MZSP: 112361, 1 shell, 112351, 1 shell, 112423, 2 shells, 112425, 1 shell.

Etymology. The specific epithet refers to Latin word molaris , grinder tooth, an allusion to the largely developed spiralis tooth at peristome.

Systematic remarks. The main character of the genus is the deviation of the growth axis in the last whorl towards right, causing a deformation from what is expected as a “normal” growth of whorls, only shown in the young specimens ( Fig. 48 ). The great development of the spiralis tooth in inner region of the parietal peristome is the main character distinguishing Streptartemon molaris from the other congener species ( Simone, 2006). The single known species that possess it is S. extraneus Haas, 1955 , from Pará, but the spiralis tooth is much larger in S. molaris , besides, the great development of the remaining peristome tooth and a smaller degree of shell deviation are additional distinctive characters. The rectangular basalis tooth is also rarely found in other congener species, it is found in S. abunaensis ( Baker, 1914) , from Mid-West Brazil, and S. cumingianus (Pfeiffer, 1849) , from Ceará to Pernambuco, from which S. molaris differs in lacking a palatal tooth, and in S. quixadensis ( Baker, 1914) , from which S. molaris differs by the more discoid shape and the wider aperture.

Figures

FIGURES 35 – 45. Type shells. Figs. 42 – 45, Anctus prolatus n. sp. holotype MZSP 112450 (L 25.2 mm); Fig. 35, frontal view; Fig. 36, same, right view; Fig. 37, same, dorsal view; Fig. 38, same, anterior view; Fig. 39, same, apical view; Fig. 40, paratype MZSP 111826 (L 24.1 mm), apertural view; Fig. 41, same, slightly left view; Figs. 42 – 45, Streptartemon molaris n. sp. shell of holotype MZSP 112451 (W 8.7 mm); Fig. 42, inferior view; Fig. 43, apical view; Fig. 44, apertural view; Fig. 45, same, detail of aperture.

FIGURES 46 – 54. Shells. Figs. 46 – 48: Streptartemon molaris n. sp.; Fig. 46, paratype MZSP 111843 (W 7.6 mm), apertural view; Fig. 47, same, detail of aperture in slightly inferior view; Fig. 48, paratype MZSP 112366, young specimen (W 6.1 mm), apertural view; Fig. 49, Lamellaxis cf. gracilis, MZSP 112406, apertural view (L 7.1 mm); Fig. 50, same species, MZSP 112354, apertural view (L 8.6 mm); Figs. 50 – 54, Beckianum beckianum; Fig. 51, MZSP 112411 (L 6.5 mm), apertural view; Fig. 52, same, right view; Fig. 53, same, dorsal view; Fig. 54, MZSP 111542 (L 4.8 mm), apertural view; Fig. 55, dorsal view.