Conus (Plagioconus) mermuysi (Roosen, Langeveld,2025)

Diagnosis ⁽¹⁾

Large, elongated Plagioconus species, with a high, dome shaped spire and indistinct spiral sculpture on the shoulder. Whorls flattened, suture deeply incised. Subsutural flexure shallow.

Dimensions ⁽¹⁾

NMR-993000100895: SL: 70.9 mm; MD: 25.7 mm; AH: 51.0 mm; RSH: 0.28; PMD: 0.85.

NMR-993000013010: SL: 84.3 mm; MD: 31.6 mm; AH: 62.4 mm; RSH: 0.26; PMD: 0.87.

RGM.226135 – SL: 63.0 mm; MD: 24.6 mm; AH: 42.8 mm; RSH: 0.30; PMD: 0.95. СА-HJ1 - SL: 93 mm; MD: 35 mm; AH: 66 mm; RSH: 0.29; PMD: 0.92.

Description ⁽¹⁾

Large, club-shaped shell reaching at least 93 mm in height, but probably could exceed 100 mm (RGM.1427219, when complete). Protoconch only partially preserved and consists of at least two smooth, glossy whorls. Spire very high, with at least 10 teleoconch whorls (could be more but the spire is abraded in all adult specimens), dome shaped, early spire whorls cari-nated above the suture, suture deeply incised. On young specimens, the carina can be beaded. Later spire whorls nearly flat, with faint spiral threads. Subsutural flexure of moderate depth, moderately curved and strongly asym-metrical. Early spire whorls show weak nodes just above the suture on the holotype. Last whorl convex with the maximum diameter of the shell relatively far below the suture. Last whorl elongate, conical, not constricted. Si-phonal canal straight, siphonal fasciole swollen, but in-distinct. Aperture narrow with subparallel margins, only widening near the anterior. Some relatively strong spiral grooves are visible on the base of all specimens. Colour pattern not preserved.

Type locality ⁽¹⁾

Winterswijk-Miste, artificial exposure (Miste-3) at Heenkamppieperweg 12 (The Netherlands).

Type stratum ⁽¹⁾

Groote Heide Formation, Aalten Member, Ticheloven or Miste Bed.

Age ⁽¹⁾

Late Early to Early Middle Miocene, Late Burdi-galian to Langhian.

Etymology ⁽¹⁾

The specific epithet honours Stef Mermuys, who made the latest artificial exposures in Winterswijk-Miste possible.

Ecology ⁽¹⁾

The holotype, paratype 2, paratype 3 and paratype 4 were found in a shallow marine clayish sand deposit (Groote Heide Formation, Aalten Member, Tich-eloven or Miste Bed). Although the exact layer from which paratype 1 originated is unknown, its occurrence in the Bislicher Schichten suggests a similar environ-ment.

Distribution ⁽¹⁾

Middle Miocene, late Burdigalian - Serravallian: Dingden, Woltrup (Germany) and Winterswijk-Miste (The Netherlands).

Discussion ⁽¹⁾

In the NMR collection, paratype 1 was identified as Lautoconus clavatulus d'Orbigny, 1852. However, that species stays smaller, has a more pronounced spiral sculpture near its siphonal canal and is much wider in outline.

In Janssen (1984), paratype 2 was referred to as Conus aquensis d'Orbigny, 1852 (Fig. 8). That species differs from Plagioconus mermuysi spec. nov. by its smaller size, a lower spire, a larger apical angle and more pronounced spiral sculpture near its siphonal canal. Also, the whorls are less concave in P. mermuysi spec. nov. and in C. aquensis from its type locality in France the carina keeps its beaded sculpture on relatively young whorls. Plagioconus mermuysi spec. nov. can be confused with other species within the genus Plagioconus.

Plagioconus austriaconoe (Sacco, 1893) also has a deeply incised suture and a more elevated spire, but can be distinguished from P. mermuysi spec. nov. by its deeper and stronger curved subsutural flexure, its lower spire (see RSH comparison in Fig. 9) and its more pronounced spiral sculpture. Moreover, P. austriaconoe is usually found in offshore clays (Harzhauser & Landau, 2016), suggesting an ecology different from the new species.

Another similar species is the widespread P. puschi (Michelotti, 1847), which can be separated from the new species by its convex spire whorls and its deeper and stronger curved subsutural flexure. The relative height of the maximum diameter is also closer to the shoulder in P. puschi.

Further comparison shows that P. mermuysi spec. nov. can be easily separated from all vaguely similar Plagioconus species by their relatively high spire and low position of the maximum diameter (Fig. 9). The two specimens that show a higher PMD are damaged around the PMD (CA-HJ1) or on the siphonal canal (RGM 226.135), distorting the measurements we took. All data of other species were retrieved from Harzhauser & Landau (2016).

Remarks ⁽¹⁾

Even though this is a large species, very few adult specimens are currently known. This might suggest it is a rare species at the localities studied herein, or that it is often misidentified as Lautoconus clavatulus.

The cone shell identified as Conus austriaconoe Sacco, 1893 in Kautsky (1925) might belong to Plagioconus mermuysi spec. nov. based on its dome shaped spire, moderately deep subsutural flexure and deeply incised suture. However, without examining the specimen (which could not be traced at this moment), this cannot be established with any certainty.

During this study, the large specimen from Dingden (NMR993000013010) started to show preliminary signs of degradation caused by pyrite oxidation. Specimen CA-HJ1 is even larger than the Dingden specimen, but was repaired by the original collector. Thus, in reality it is much more damaged than currently visible. Therefore, we designate the smaller but stable specimen from the Miste-3 artificial exposure (NMR993000100895) as the holotype.

Bibliografia Consultata

• (1) - Roosen, M.; Langeveld, B. W. (2025). "New species of Conasprella Thiele, 1929 and Plagioconus Tucker & Tenorio, 2009 (Gastropoda, Conidae), previously identified as Lautoconus clavatulus (d'Orbigny, 1852) and Conus aquensis d'Orbigny, 1852, from the Miocene of Winterswijk-Miste (The Netherlands), Dingden and Woltrup (Germany)". Cainozoic Research. 25 (2): 139–148.

• (2) - Kautsky, F. 1925. Das Miocän von Hemmoor und Basbeck Os-ten. Abhandlungen der Preußischen Geologischen Landes-anstalt, Neue Folge 97: 1-255.