Bittium miradouroense, Sacchetti & Landau & Ávila, 2023

Sacchetti, Claudia, Landau, Bernard & Ávila, Sérgio P., 2023, The Lower Pliocene marine gastropods of Santa Maria Island, Azores: Taxonomy and palaeobiogeographic implications, Zootaxa 5295 (1), pp. 1-150 : 31-32

Bittium miradouroense nov. sp.

Plate 1 J 1 -J 2 , K 1 -K 2

Type material. Holotype DBUA-F 1034-5 , height 6.8 mm, width 1.9 mm ( Plate 1 J 1 -J 2 ), with two paratypes DBUAF 1034-6(1) ( Plate 1 K 1 -K 2 ), DBUA-F 1034-6 (2), height 5.3 mm, width 1.9 mm, Macela viewpoint, Santa Maria Island , Azores.

Other material. Maximum height 6.8 mm, width 1.9 mm. DBUA-F 1034-5 (33), Miradouro da Macela, Santa Maria Island, Azores, Touril Complex, Lower Pliocene.

Type locality. Miradouro da Macela , Santa Maria Island, Azores .

Type stratum. Touril Complex.

Age. Lower Pliocene , Zanclean .

Etymology. Named after the viewpoint (miradouro) de Macela. Bittium gender neuter.

Diagnosis. Shell of medium size for genus, ten initially straight sided, later weakly convex teleoconch whorls, separated by deep suture, sculpture of broad rounded ribs, crenulating adapical suture, spiral sculpture weak, two peribasal cords.

Description. Shell small, turriculate, with tall, slender spire apical angle about 23°. Protoconch not well preserved (see intraspecific variation below). Teleoconch of ten initially straight sided, later weakly convex whorls separated by a narrow, deeply impressed, undulating suture. Sculpture of broad rounded, slightly opisthocline to orthocline ribs, about 12 on penultimate whorl, extending between suture and crenulating abapical suture. Last two whorls with one or two varices per whorl. Spiral sculpture weak, possibly four low flattened cords on spire whorls. Axial sculpture predominant, without tubercles produced at intersections. Last whorl weakly convex, strongly constricted at base; base delimited by two peribasal cords, the lower one stronger, three further weak cords over base. Aperture subquadrate, outer lip simple, columella excavated mid-whorl inside filled with matrix.

Intraspecific variation. Within the specimens from Macela viewpoint there is some variability as to the number of ribs and the number and strength of the spiral cords. Specimens from Ponta do Castelo look a little different in having slightly fewer ribs and the spiral sculpture is present on the first four teleoconch whorls and rapidly fades on the later whorls, except for one strong cord, just above the suture. These differences may be accentuated by the different preservation: the specimens from Macela viewpoint are calcitic pseudomorphs, whereas those from Ponta do Castelo have a decalcified surface and are therefore decorticated. We provisionally consider all these specimens conspecific. The protoconch in one of the Ponta do Castelo specimens, although poorly preserved, seems non-planktotrophic, of possibly 2-2.5 smooth convex whorls.

Discussion. Bittium miradouroense nov. sp. is characterized by its broad rounded axial ribs that crenulate the suture and weak spiral sculpture that does not form tubercles over the ribs. This is a very distinctive species that cannot be usefully compared with any extant European species. Bittium watsoni ( Jeffreys, 1885) , from deep waters of the Iberian Peninsula southwards to Senegal including the Canary Islands is similar in having wide, rounded ribs and weak spiral sculpture but, in that species, the ribs fade on the mid-spire whorl so that the last three whorls are smooth, or almost so, and the spiral sculpture is even weaker.

Distribution. Lower Pliocene: Atlantic, Santa Maria Island, Azores (this paper).

Figures

PLATE 1. A. Danilia pterostomus (Bronn, 1861), height 5.0 mm, width 4.0 mm, Forno da Cré (figure taken from Bronn in Hartung, 1861, pl. 19, fig. 2). B1-B2. Emarginula octaviana Coen, 1939, DBUA-F 487-1, height 1.8 mm, diameter 3.0 mm, Ponta do Castelo. C. Bolma cf. rugosa (Linné, 1767), DBUA-F 471-3, diameter 4.1 mm, Ponta do Castelo. D1-D5. Turbo hartungi Bronn 1861, DBUA-F 1295-1, height 9.0 mm, width 8.0 mm, Malbusca (east cave). E1-E3. Nerita cf. funata Dujardin, 1837, DBUA-F 917-1, height 4.0 mm, width 6.0 mm, Ponta do Castelo. F1-F2. Thericium crenulosum (Bronn, 1862), height 10.0 mm, width 6.0 mm, Ponta do Norte lighthouse, LNEG collection (unnumbered). G1-G2. Thericium hartungi (Mayer, 1862), height 29.0 mm, width 13.0 mm, Pinheiros (figure taken from Bronn in Reiss, 1862, pl. 1, fig. 11). H1-H2. Thericium incultum (Mayer, 1862), DBUA-F 1034-2, height 23.0 mm, width 10.0 mm, Macela viewpoint. I1-I2. Thericium incultum (Mayer, 1862), DBUA-F 1027-1, height 29.0 mm, width 11.0 mm, Malbusca II. J1-J2, K1-K2. Bittium miradouroense nov. sp., Holotype DBUAF 1034-5, height 6.8 mm, width 1.9 mm (J); Paratype DBUA-F 1034-6(1), height 5.3 mm, width 1.9 mm (K), Macela viewpoint. L1-L2, M1-M2. Bittium nov. sp., DBUA-F 488-2, height 4.5 mm, width 1.8 mm (L), height 4.2 mm, width 1.7 mm (M), Ponta do Castelo.

PLATE 2. A1-A2. Bittium nanum (Mayer, 1864), DBUA-F 1296-2, height 4.9 mm, width 2.0 mm, Malbusca. B. Tenagodus (Tenagodus) obtusus (Schumacher, 1817), DBUA-F 1283-2, height 12.0 mm, width 11.0 mm, Ponta do Castelo. C. Epitonium sp., DBUA-F 931-1, height 4.0 mm, width 2.8 mm, Pedra-que-pica. D1-D3. Janthina krejcii, SMF10135a, height 25.0 mm, diameter 32.0 mm, Macela viewpoint (pictures from Beu, 2017, fig. 26). E1-E3. Janthina typica (Bronn, 1861), DBUA-F-428, height 19.0 mm, diameter 21.0 mm, Ponta do Castelo, (pictures from Beu, 2017, fig. 25). F.Cheilea equestris (Linnaeus, 1758), DBUA-F 1283-1, diameter 30.0 mm, Ponta do Castelo. G1-G3. Hipponix sulcatus (Borson, 1820), DBUA-F 937-1, height 5.3 mm, diameter 14.0 mm, Ponta do Castelo. H1-H2. Euspira atlantica (Mayer, 1862), height 16.0 mm, diameter 19.0 mm, Ponta do Norte lighthouse, LNEG collection (unnumbered). I. Triphorid s.l., DBUA-F 471-5, height 3.2 mm, width 1.3 mm, Ponta do Castelo. J1-J2. Cerithiopsis cf. tubercularis (Montagu, 1803), DBUA-F 1023-1, height 3.0 mm, width 1.2 mm, Ponta do Castelo. K. Petaloconchus intortus (Lamarck, 1818), DBUA-F 946-2, height 13.0 mm, width 6.0 mm, Ponta dos Cedros. L. Thylacodes arenarius (Linnaeus, 1758), DBUA-F 869-1, height 33.0 mm, width 24.0 mm, Ponta dos Cedros. M1-M3. Alvania cancellata (da Costa, 1778), DBUA-F 1296-3, height 4.0 mm, width 2.2 mm, Malbusca.