Bittium jadertinum

Bittium jadertinum (Brusina, 1865) (Fig. 5G 1-G 3) Cerithium jadertinum Brusina, 1865: 16. Bittium jadertinum – Landau et al. 2004: 10, pl. 2, fig. 1. — Wesselingh et al. 2012: 39, figs 6-9. — Chirli & Forli 2017: 43, fig. 12f. For more, see synonymy list in Landau et al. (2004). MATERIAL AND DIMENSIONS. — Maximum height 3.8 mm, width 1.3 mm. — RGM.1365269 (1), leg. AWJ; RGM.1365073 (3), leg. AWJ. SPECIES CHARACTERISATION. — Robust Bittium with a very slightly convex whorl profile; four regularly spaced spirals are intersected at regular distances by orthocline to very slightly prosocyrth axial ribs of similar strength with regular knobs on the intersections; six spirals on the shells base. DISTRIBUTION. — Upper Pliocene: western Mediterranean, S. Spain (Landau et al. 2004). — Lower Pleistocene: Selsoif, NW France (this paper); central Mediterranean, Italy (Chirli & Forli 2017). — Middle Pleistocene: NSB, the Netherlands (Wesselingh et al. 2023). — Upper Pleistocene: NSB, the Netherlands (RGM collections); western Mediterranean, Balearic Islands (Cuerda Barceló 1987). Today it occurs from the North Sea to North Africa, and into the Mediterranean (Poppe & Goto 1991) REMARKS Currently WoRMS (2023) considers B. jadertinum a synonym of Bittium reticulatum (da Costa, 1778). The basis for their synonymy is unclear, as Verduin (1982) is given as the most recent authority in which that author clearly accepted B. jadertinum as a valid species. As summarised by Landau et al. (2004), the main differences between the two species are that B. jadertinum has four equidistant spiral cords and no varices, except possibly on the last 1.5 whorls, whereas B. reticulatum has spiral 1 and 2 closer-set and numerous varices along all teleoconch whorls. Both have a multispiral protoconch with a small nucleus. Within large Late Pleistocene samples from the southern North Sea, we are able to separate the reticulatum and jadertinum morphotypes (Wesselingh et al. 2012; 2023). The species B. pingue Landau et al., 2018, from Assemblage I of Renauleau, NW France, has similar rib architecture but is much smaller and has a wider apical angle.