Monoplex heptagonus ( Brocchi, 1814 )

Kovács, Zoltán & Vicián, Zoltán, 2017, Middle Miocene Tonnoidea and Ficoidea (Caenogastropoda) assemblages from Letkés (Hungary), Fragmenta Palaeontologica Hungarica 34, pp. 75-104 : 88-90

Monoplex heptagonus ( Brocchi, 1814)

(Figs 33–34)

1814 Murex heptagonus – BROCCHI, p. 404, pl. 9, fig. 2.

1966 Cymatium (Ranularia) heptagonum vindobonicum Cossmann & Peyrot – STRAUSZ, p. 248, pl. 29, fig. 7.

2013 Monoplex heptagonus (Brocchi) – LANDAU et al., p. 128, pl. 18, figs 8–10 (cum syn.).

Material – 106 specimens (SL 10–25); HNHM: M.62.835., INV 2017.677. (Figs 33–34), INV 2017.678. (7) , 97 specimens in private collections.

Description – Small shell, moderately elevated, step-like spire, four, convex, shouldered teleoconch whorls, slightly convex, subtrigonal last whorl with sloping sutural ramp. Ovate aperture, denticulate outer lip thickened by labral varix, long, narrow, straight siphonal canal, plicate columella, thickened parietal callus, long fasciole. Spiral sculpture of three well-developed primary cords on the spire whorls and 5–6 on the last whorl, one secondary cord in interspaces, axial sculpture of broad, rounded ribs (7–8 on the last whorl), growth lines and one varix on the last whorl, tubercles at intersections.

Remarks – The morphology of the species is very similar to that of M. corrugatus (see BAŁUK 1995), but it differs in scalate spire, more strongly shouldered whorls and more raised spiral cords. The M. heptagonus material of Letkés shows moderate intraspecific variability in development of sculpture. The species was abundant in the mollusc assemblage.

Distribution – Burdigalian: PMS ( Italy), Badenian: CP ( Austria, Bulgaria, Hungary, Poland, Romania), Serravallian: PMS ( Turkey), Tortonian: PMS ( Italy). For Pliocene range see VAN DINGENEN et al. (2016).

Monoplex sp.

(Figs 35–36)

Material – One adult specimen (SL 30.5); in private collection.

Description – Squat, subovate shell, moderately elevated, conical spire, protoconch missing, four, convex, shouldered teleoconch whorls with concave sutural ramp, convex last whorl. Ovate aperture, outer lip thickened by labral varix, six denticles within, long, narrow, slightly curved siphonal canal, plicate columella, thickened parietal callus. Spiral sculpture of four narrow cords on the ramp and six cords on the penultimate whorl, and eight primary cords (five adapical divided by median grooves) on the last whorl, secondary cords in interspaces, axial sculpture of broad, rounded ribs (7 on the last whorl), fine growth lines and one varix on the last whorl.

Remarks – The morphology differs from that of both M. heptagonus and M. subcorrugatus in broader and conical spire, narrower aperture and much finer spiral cords. The specimen probably represents a new species. Distribution – Badenian: CP (Letkés, Hungary).