Costoanachis semicostata
Creators: name: Sacchetti, Claudia
name: Landau, Bernard
name: Ávila, Sérgio P.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Neogastropoda
Columbellidae
Costoanachis
Costoanachis semicostata

description: Costoanachis semicostata (Sacco, 1890)
Plate 4 I 1 -I 2
* Columbella (Anachis) semicostata Sacco 1890: 60, pl. 2, fig. 86.
Anachis (Ecostoanachis) semicostata (Sacco, 1890) —Malatesta: 318, pl. 25, fig. 8.
Columbella (Anachis) semicostata Sacco in Bellardi, 1890 — Ferrero Mortara et al. 1984: 186, pl. 58, fig. 11.
Anachis semicostata (Sacco in Bellardi, 1890)— Chirli 2002: 5, pl. 1, figs. 5-12, pl. 2, figs. 1-12.
Anachis semicostata (Sacco in Bellardi, 1890)— Sosso & Dell’Angelo 2010: 41, 58 unnumbered fig. bottom centre.
Anachis semicostata (Sacco in Bellardi, 1890)— Brunetti & Cresti 2018: 80, fig. 306.
Columbella (Anachis) semicostata Sacco in Bellardi— Kolokotronis 2022, p. 5, figs. 1, 2.
Santa Maria material examined. Maximum height 6.9 mm, width 3.0 mm. DBUA-F 1034-4 (3), Macela viewpoint; DBUA-F 540-B (1), Ponta dos Frades; DBUA-F 1287-B (1), DBUA-F 1189- B, E (4), Pedra-que-pica, Santa Maria, Azores, Touril Complex, Lower Pliocene.
Description. Shell small, fusiform. Protoconch tall dome-shaped multispiral, consisting of 3.25 smooth, convex whorls. Junction with teleoconch marked by sinusigera. Teleoconch of five weakly convex whorls with periphery at abapical suture. Suture deeply impressed, linear. Axial sculpture of about 14 opisthocline ribs, extending between the sutures that weaken rapidly on the third whorl, becoming obsolete, or almost so, on the last 2.5 whorls. Spiral sculpture absent. Last whorl evenly rounded, moderately constricted at base, about eight rounded spiral cords over siphonal fasciole. Aperture elongate (damaged in Azores material); outer lip slightly thickened by varix, bearing six or seven robust, elevated denticles within, D2 and D3 slightly stronger; anal sinus weakly developed, narrow U-shaped; siphonal canal open, relatively broad, notch at tip. Columella excavated in upper third, straight below, bearing row of four or five robust tubercules. Columella callus thickened, sharply delimited, adherent. Parietal callus thin, not develop in some species.
Intraspecific variability. The species is highly variable in the number of axial ribs on the early teleoconch whorls and their extent. In most specimens the ribs stop abruptly on the second half of the third whorl, but they can fade earlier or persist later in some specimens. Some variability is also seen in the strength of the labral denticles and the presence or absence of a thin parietal callus. The Azorean specimens are typical for the species with the axial sculpture weakening on the third teleoconch whorl.
Discussion. Costoanachis semicostata (Sacco, 1890) is characterised by the early disappearance of the axial sculpture. Costoanachis semiplicata (Sacco, 1890) from the upper Miocene of Italy is closely similar. The syntype illustrated by Ferrero Mortara et al. (1984: pl. 58, fig. 10) seems to have broader ribs that persist onto the penultimate whorl and the base is slightly less constricted. Costoanachis procorrugata (Sacco, 1890) (syntype illustrated by Ferrero Mortara et al. 1984, pl. 58, fig. 9) from the middle Miocene Colli Torinesi of Italy and Costoanachis rectecostata (Sacco, 1890) (syntype illustrated by Ferrero Mortara et al. 1984: pl. 58, fig. 3) both differ in having broader ribs that persist onto the last whorl.
Costoanachis semicostata (Sacco, 1890) is a typical Italian Pliocene Mediterranean species, recently also described from the eastern Mediterranean Pliocene (Kolokotronis 2022), and certainly present in the western Mediterranean Estepona Basin assemblages of Spain (BL unpublished data). It has not previously been recorded from the Atlantic, highlighting the ancient biogeographical relationships of the gastropod Azorean fauna with that of the Mediterranean Sea (Ávila 2005; Ávila et al. 2022), a pattern that still holds in the present-day (Ávila 2000b; Ávila et al. 2009a, 2015a; see Freitas et al. 2019).
Distribution. Lower Pliocene: Atlantic, Santa Maria Island, Azores (this paper); western Mediterranean, NE Spain (NHMW coll.); central Mediterranean, Italy (Ferrero Mortara et al. 1984; Chirli 2002; Sosso & Dell’Angelo 2010; Brunetti & Cresti 2018). Upper Pliocene: western Mediterranean, Estepona Basin, S. Spain (NHMW coll.); central Mediterranean, Italy (Malatesta 1974). Pliocene (indeterminate): eastern Mediterranean, Cyprus (Kolokotronis 2022).
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 page 67, DOI: 10.11646/zootaxa.5295.1.1, http://zenodo.org/record/7965273