Macromphalina depressa
Creators: name: Sacchetti, Claudia
name: Landau, Bernard
name: Ávila, Sérgio P.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Vanikoridae
Macromphalina
Macromphalina depressa

description: 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).
description: Published as part of Sacchetti, Claudia, Landau, Bernard & Ávila, Sérgio P., 2023, The Lower Pliocene marine gastropods of Santa Maria Island, Azores: Taxonomy and palaeobiogeographic implications, pp. 1-150 in Zootaxa 5295 (1) on pages 50-51, DOI: 10.11646/zootaxa.5295.1.1, http://zenodo.org/record/7965273