Bela? robusta, Scarponi & Bella & Dell’Angelo & Huntley & Sosso, 2016

Scarponi, Daniele, Bella, Giano Della, Dell’Angelo, Bruno, Huntley, John Warren & Sosso, Maurizio, 2016, Middle Miocene conoidean gastropods from western Ukraine (Paratethys): Integrative taxonomy, palaeoclimatogical and palaeobiogeographical implications, Acta Palaeontologica Polonica 61 (2), pp. 327-344 : 337-338

Bela? robusta sp. nov.

Figs. 5L, M , 6B , 7A ; SOM 1: fig. 3F, SOM 2.

Etymology: From Latin robustus, hard, firm; named after the solid shape of the teleoconch.

Type material: Holotype, MGGC-24518 , adult, well-preserved shell . Paratypes, MGGC 24519 /1–14 from the type locality (SOM 2) .

Type locality: Varovtsi , Ukraine .

Type horizon: Massive, white sandstone of the Pidhirtsi Beds, early Serravallian (~14.0−12.7 Ma).

Material.— Type material only.

Diagnosis.—A relatively large, biconical Bela (shell lengthm 6.7 mm, sd 2.0 mm; shell widthm 3.2 mm, sd 0.7 mm), with multispiral protoconch (lengthm 0.57 mm, sd 0.04 mm; widthm 0.59 mm, sd 0.02 mm), characterised by few and relatively strong riblets. Teleoconch whorls rounded with a sculpture of relatively spaced ribs (max. 11 on the second whorl) and a dense pattern of spiral elements of variable thickness. Outer lip thin, straight in profile, anal sinus on sutural ramp, siphonal canal almost indistinct.

Description.—Shell small-sized, biconical, solid; spire slightly turreted (0.32 the shell length; sd 0.03); last whorl elongated (lengthm 4.7 mm, sd 1.2 mm), slightly rounded. Protoconchm dome-shaped of 2.2 convex whorls (sd 0.1 wh); nucleus small, smooth as the remaining except for the final-quarter, where 3−4 faint cordlets override curved, relatively thick riblets. Protoconch-teleoconch boundary well-marked by a sinusigera. Teleoconchm of 4.5 whorls (sd 0.7 wh), slightly convex in profile, with strong axials and subdued spiral sculpture; suture undulating. Axial sculpture of thick, rounded, narrowly spaced ribs (usually 10 on the second whorl) extending across sutures on spiral whorls, fading out towards the base on last whorl; growth lines dense, evident. Spiral elements densely indented, the thinner ones often truncated, the thicker sometimes beaded by growth lines. Aperture elongate, relatively narrow, sub-rectangular, about half of the shell height (lengthm 3.3 mm, sd 0.8 mm); siphonal canal very short, almost indistinct; outer lip thin, smooth inside, straight in profile; anal sinus relatively broad, commonly L-to-C shaped, on the sutural ramp; columellar lip slightly bent.

Remarks.—This species is tentatively assigned herein to the genus Bela sensu lato on the basis of comparable teleoconch and protoconch sculptural pattern and overall shell profile and dimensions. Close affinities are considered also with the genus Brachycythara Woodring, 1928 . Indeed, the shell differences between the genera Brachycythara and Bela are minor and mainly refer to the following: Brachycythara shells are smaller (length <9 mm), stouter, with the outer lip slightly thickened and parietal callus moderately developed; protoconch sculpture is of crowded riblets whereas teleoconch sculpture is of stout axial folds overridden by finer with respect to Bela ) spiral elements ( Powell 1967; Smriglio et al. 2007). Here, the absence of: (i) parietal callus; (ii) lirae inside the outer lip, and (iii) a dense pattern of protoconch riblets suggest caution in the assignment of this new species to the genus Brachycythara . However, the current definitions of the genera Bela and Brachycythara are rather broad and need refining ( Smriglio et al. 2007; Scarponi et al. 2014b). For instance, Brachycythara beatriceae Mariottini,

2007 and B. atlantidea ( Knudsen, 1952) , two Mediterranean species that show similarities regarding the teleoconch with our material, were recently placed within the genus Bela sensu lato (see Mariottini et al. 2012). Bela? robusta can be easily distinguished by B. atlantidea and B. beatriceae by a smaller and less sculptured protoconch, and a less regular teleoconch spiral pattern. Hence, no further comparative analyses were performed.

Stratigraphic and geographic range.—Pidhirtsi Beds, early Serravallian of the Central Paratethys.

Figures

Fig. 5. SEM images of shell features of new conoidean gastropods from early Serravallian of western Ukraine, Varovtsi (A–E, I–M), Horodok (G), and Velyka Levada (F, H). A. Mangelia angulicosta sp. nov., MGGC-24506/6. B–D. Mangelia larga sp. nov. B. MGGC-24508/11. C. MGGC-24508/1. D. MGGC-24508/12. E. Mangelia pseudorugulosa sp. nov., MGGC-24510/9. F–H. Mangelia odovychenae sp. nov. F. MGGC-24512/1. G. MGGC- 24512/10. H. MGGC-24512/topotype. I–K. Bela varovtsiana sp. nov. I. MGGC-24517/8. J. MGGC-24517/5. K. MGGC-24517/6. L, M. Bela? robusta sp. nov. L. MGGC-24519/8. M. MGGC-24519/1. Views: A1–L1, B, F, I, apertural;A2−L2, C, G, J, dorsal; A3, D, E3, H, K, M, lateral. Scale bars 1 mm.

Fig. 6. Photomicrographs of holotype shell of new conoidean gastropods from early Serravallian of western Ukraine, Varovtsi (A, B) and Horodok (C). A. Bela varovtsiana sp. nov., MGGC-24516. B. Bela? robusta sp. nov., MGGC-24518. C. Pyrgocythara turrispiralata sp. nov., MGGC-24514. Views: A1−C1, apertural; A2−C2, dorsal;A3−C3, lateral. Scale bars 1 mm.

Fig. 7. SEM images of protoconch features of conoidean gastropods from early Serravallian of western Ukraine, Varovtsi (A, C–F) and Horodok (B). A. Bela? robusta sp. nov., MGGC-24519/8. B. Pyrgocythara turrispiralata sp. nov., MGGC-24515/11. C. Raphitoma cf. R. ringicula (Boettger, 1902), MGGC-24522/5. D. Andonia sp. aff. A. transsylvanica (Hoernes and Auinger, 1890), MGGC 24523/2. E. Teretia cf. T. turritelloides Bellardi, 1847), MGGC-24524/5. F. Haedropleura sp. aff. H. septangularis (Montagu, 1803), MGGC-24520/6. Views: A1, B1, C–F, lateral; A2, B2, apical. Scale bars 0.1 mm.