Balearena gymnesica, Altaba, Cristian R., 2007

Altaba, Cristian R., 2007, A new genus and species of Enidae (Gastopoda: Pulmonata) from the Quaternary of the Balearic Islands (Western Mediterranean), Zootaxa 1595, pp. 43-52 : 45-46

Balearena gymnesica sp. nov.

( Figures 1–3 )

Type material: Holotype, MZB 2005-1022; paratypes (three complete, four incomplete), MZB 2005-1023. Additional paratypes (five each: one complete and four incomplete) deposited in MBCN, CRA-10862, CRA- 10907.

Type locality: Top level of the low (2 m) coastal cliff at Cala Pudent, in Camp de Tir, the eastern sector of Es Carnatge, in Palma de Mallorca, Mallorca Island, Balearic Islands (39º 32’ N, 2º 42’ E; UTM coordinates 31S DD 7477). This terrace, overlying various Upper Pleistocene strata, is formed by terrigenous clay mixed with marine biogenetic sand, marking at its top the latest marine regression at the end of the Neotyrrhenan, the last interglacial transgressive sequence recorded in Mediterranean strata.

Distribution: Known only from the northern Balearic Islands, or Gymnesics. The type stratum was formed at the onset of the Würm II glacial cycle, with an age of ca. 80,000 years ( Cuerda 1989; Hillaire-Marcel et al. 1996; González-Hernández et al. 2001). Moderately common in late Pleistocene coastal paleosoils, fossil beaches and eolianites in Mallorca, Menorca and Cabrera ( Cuerda 1989, 1993; Altaba 1993). The species is also reported from older cave fillings in coastal cliffs in Menorca, putatively dated as latest Miocene ( Quintana 1995) but likely being Plio-Pleistocene cave fillings.

Description: Based on 17 specimens, plus numerous fragments, all from the type locality and stratum. Shell typically enid, with spire conspicuously slender and aperture gently expanded basally, rather thin, fragile. Spire acute elongated, whorls 7 1/8–7 1/4, spire angle approximately 30o. Profile of spire slightly concave from whorls 2 to 5, becoming convex only in later whorls; general shape thus lightly fusiform. Suture very deep in early whorls, gradually becoming less pronounced but always incised. Whorls rotund initially, then less so; penultimate whorl compressed near suture, giving sinuous profile; last 1 1/2 whorls uniformly flattened laterally; last whorl slightly descending. Aperture 1/3 of shell height, suboval, slightly oblique, gently expanded at rounded lower half, with columellar, palatal margins nearly straight, parallel. Peristome sharp, somewhat reflexed along palatal margin more reflexed along columellar margin, gently flaring, its parietal insertions widely distant but joined by distinctive, shallow callus. In full-grown specimens one blunt angular tooth often present. Columella broadened internally, forming narrow flat area dominated by shallow vertical fold. Umbilicus very narrow slit, partially occluded by reflected columellar edge. Embryonic whorls 1 1/4, distinct, having sculpture (discernible only in best preserved specimens) consisting of regular, shallow radial grooves running from suture on upper side, thin spiral lines on bottom half of whorls ( Fig. 2 ). Teleoconch sculpture formed by low but rough, uneven, shallow radial wrinkles, giving dull shine. In approximately first two teleoconch whorls, delicate, interrupted spiral sculpture, subjugated to radial wrinkles. Color apparently uniform olive-brown, except for white peristome, without any markings. Height 13.5–16.7 mm, width 5.6–6.6 mm.

Etymology: The specific epithet refers to the Gymnesics, or northern Balearic Islands, where the species was endemic.

Remarks: The series of nine specimens discussed and figured by Cuerda (1959, 1989), collected in the same stratum as the holotype, and kept in his collection now in SHNB (no catalog number), are also referred

Figures

FIGURE 1 – 2. 1. Balearena gymnesica gen. nov., spec. nov. Holotype, upper coastal cliff at eastern edge of Es Carnatge, Palma de Mallorca, Mallorca island, Balearic Islands, Western Mediterranean. Shell length 16.7 mm; scale bar 2.0 mm. Not shown are a thin encrustation over most of the first whorl and minimal fractures on the peristome. 2. Protoconch sculpture of Balearena gymnesica. This reconstruction is based on partial remains of these delicate features that are observable in various specimens. Scale bar 0.5 mm.

FIGURE 3. Comparison of shells of Mastus pupa (top row; Korbous, Tunisia) and Balearena gymnesica (bottom row; Es Carnatge, Mallorca). Scale bar 10 mm.