Macromphalina depressa (Boettger, 1907)

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 : 50-51

Macromphalina depressa (Boettger, 1907)

Plate 3 E 1 -E 3

* Narica depressa Boettger 1907: 175 .

Vanikoro depressa (Boettger) — Zilch 1934: 247, pl. 13, fig. 60.

Megalomphalus depressus (Boettger, 1907) — Bałuk 1995: 169, pl. 5, fig. 7.

Macromphalina depressa (Boettger, 1907) — Landau et al. 2004a, 76, pl. 16, fig. 3 (except 3e), pl. 17, fig. 4.

Macromphalina cf depressa (Boettger, 1907) — Brunetti & Cresti 2018: 50, fig. 135.

non Macromphalina depressa ( Seguenza, 1874) — Ghisotti 1978: 160, pl. 1, figs. 2, 3, 6 (= Megalomphalus disciformis Granata Grillo, 1877).

Santa Maria material examined. Maximum height 1.4 mm, width 3.1 mm. DBUA-F 1023-3 (1), Ponta do Castelo, Santa Maria Island, Azores, Touril Complex, Lower Pliocene.

Description. Shell small, fragile, depressed, auriform, perforate, with very low depressed spire. Protoconch paucispiral, consists of 1.4 smooth convex whorls, with a medium-sized nucleus, coiled slightly obliquely to shell axis. Junction with teleoconch sharply delimited by prosocline scar. Teleoconch consists of 1.25 flattened whorls, with periphery at abapical suture. Suture linear, deeply impressed. Sculpture of numerous, rounded, subequal spiral cords, broader than their interspaces. Axial sculpture absent, except for growth lines. Last whorl greatly expanded and depressed, weakly convex and roundly angular at periphery. Base convex, devoid of spiral sculpture, but bearing prominent close-set axial growth lamellae. Aperture large, ovate. Outer lip thin, without labial varix, smooth within and regularly convex. Columella rectilinear, not thickened, forming the medial border of the wide umbilicus. Umbilicus very wide, about two-thirds diameter of base, deep, with rounded edge, walls tapering inwards gently, sculptured with strong axial growth lines within.

Discussion. The teleoconch characteristics; small, depressed shell, auriform, with a wide umbilicus and an oblique aperture, coincide well with the genus Macromphalina Cossmann, 1888 . The protoconch characteristics, as described by Rubio & Rolán (1993: 48); three to four whorls, with a sculpture of spiral cords and fine axial ribs typical of species with planktotrophic development, are not seen in this species, which has a smooth paucispiral protoconch suggestive of non-planktotrophic development. The same authors (1998) described numerous members of the genus from the Recent Caribbean, some of which also have smooth paucispiral protoconchs also suggestive of non-planktotrophic development (i.e., M. floridana Moore, 1965 , M. apexplanum Rolán & Rubio, 1998 , and M. susoi Rolán & Rubio, 1998 ). Therefore, the protoconch characteristics are not genus specific in this group ( Landau et al. 2004a: 77).

We consider the Azorean specimen conspecific with that from the Atlantic Lower Piacenzian Upper Pliocene, Estepona Basin of Spain, illustrated by Landau et al. [2004a: pl. 16, fig. 3 (except 3e), pl. 17, fig. 4)] as Macromphalina depressa (Boettger, 1907) . The spiral sculpture is not as evident in the Azorean specimen because it is somewhat decalcified. Originally described from the middle Miocene Paratethys, the Estepona occurrence was the first Pliocene record for the species. Subsequently, it has been recorded in the Lower Pliocene central Mediterranean of Italy ( Brunetti & Cresti, 2018) and now from the mid-Atlantic oceanic islands (hoc opus).

No Recent European species are similar to M. depressa . Two present-day West African species also have prominent spiral sculpture. The most similar, M. dautzenbergi Adam & Knudsen, 1969 has spiral sculpture of similar strength, but a protoconch of 2.5 whorls, which is coiled more obliquely to the axis of the teleoconch and bears some spiral sculpture. Macromphalina gofasi Rubio & Rolán, 1993 has a more elevated shell, with a strong angulation at the base and a sculpture of broader spiral cords. It again has a protoconch consisting of 2.5 whorls.

Distribution. Middle Miocene: Paratethys, Poland ( Bałuk 1995), Romania (Boettger 1907). Lower Pliocene: Atlantic, Santa Maria Island, Azores (this paper); central Mediterranean, Italy ( Brunetti & Cresti 2018). Upper Pliocene: western Mediterranean, Estepona Basin, Spain ( Landau et al. 2004a).

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 3. A. A1-A2. Alvania mediolittoralis Gofas, 1989, DBUA-F 962-2, height 2.1 mm, width 1.2 mm, Ponta do Castelo. B. Alvania sleursi (Amati, 1987), DBUA-F 471-4, height 2.0 mm, width 1.1 mm, Ponta do Castelo. C1-C2. Alvania sleursi (Amati, 1987), DBUA-F 962-3, height 3.2 mm, width 1.8 mm, Ponta do Castelo. D1-D3. Rissoina pusilla (Brocchi, 1814), DBUA-F 488-1, height 5.2 mm, width 2.1 mm, Ponta do Castelo. E1-E3. Macromphalina depressa (Boettger, 1907), DBUA-F 1023-3, height height 1.0 mm, width 1.8 mm, Ponta do Castelo. F. Calyptraea chinensis (Linnaeus, 1758), DBUA-F 926-1, diameter 18.0 mm, Malbusca 2. G1-G2. Schilderia utriculata (Lamarck, 1810), height 24.0 mm, width 15.0 mm, unknown locality, LNEG collection (unnumbered). H1-H3. Erato mayeri nov. sp., Holotype DBUA-F 1189-C, height 7.7 mm, width 5.3 mm, Pedra-que-pica. I1-I3. Erato mayeri nov. sp., Paratype DBUA-F 1291-1, height 8.9 mm, width 6.0 mm, Ponta dos Frades. J1-J4. Pseudopusula parcicosta (Bronn, 1862), DBUA-F 469-1, height 9.0 mm, width 6.5 mm, Ponta do Castelo.