Scintilla cf. violescens Kuroda & Taki, 1961

Albano, Paolo G., Steger, Jan, Bakker, Piet A. J., Bogi, Cesare, Bosnjak, Marija, Guy-Haim, Tamar, Huseyinoglu, Mehmet Fatih, LaFollette, Patrick I., Lubinevsky, Hadas, Mulas, Martina, Stockinger, Martina, Azzarone, Michele & Sabelli, Bruno, 2021, Numerous new records of tropical non-indigenous species in the Eastern Mediterranean highlight the challenges of their recognition and identification, ZooKeys 1010, pp. 1-95 : 1

Scintilla cf. violescens Kuroda & Taki, 1961 Figure 41

New records.

Israel • 1 spcm; Haifa; depth 15 m; May 1999; biogenic sediment; B.S. Galil leg.; size: L 6.9 mm, H 5.2 mm.

Remarks.

The single shell found is trapezoid-oval (L:H ratio = 1.33), slightly higher posteriorly than anteriorly, translucid-white, and has a glossy external surface. The valves are narrowly gaping, more widely in their posterior part. The umbones are prosogyrate, pointed and submedian. The commarginal sculpture consists of fine growth lines that are slightly wavy posteriorly, as well as irregular growth marks. Flat radial ribs are present in the posterior part of the shell; they are visible, upon close examination, also on the inside of the valves in the form of shallow markings. The inner surface, particularly of the right valve, is spotted by blister-like markings (Figure 41C, D ). The hinge of the right valve bears a single cardinal tooth, bent towards the anterior, and an elongated posterior lateral tooth. The left valve has two cardinals, but the anterior one is broken off (Figure 41G ); a posterior lateral is present.

Lacking further material and observations on living individuals, which are of great diagnostic importance in galeommatids, we refrained from assigning a definitive specific name to our shell. However, the overall shape, hinge dentition and the presence of radial sculpture match well descriptions of Scintilla violescens Kuroda & Taki, 1961 ( Arakawa 1961; Kuroda and Taki 1961), a species recorded from the intertidal and shallow subtidal of Thailand and Japan ( Huber 2015). In contrast to our shell, however, Kuroda and Taki (1961) mention the presence of radial sculpture on the entire surface of the valves of their type material. While our Mediterranean shell is less elongated than the specimens of S. violescens illustrated by Okutani (2000), Lützen and Nielsen (2005), and Huber (2015), it is very similar in outline to the shell shown by Arakawa (1961: fig. 5B) (which was identified by T. Kuroda and I. Taki). Scintilla violescens appears to be variable also with respect to shell size and coloration: specimens from Thailand (maximum length = 10.5 mm, n = 12 spcms) all were considerably smaller than the> 15 mm-long Japanese type ( Kuroda and Taki 1961) and had a whitish instead of pale violet color ( Lützen and Nielsen 2005), like the Israeli shell. Considering this great plasticity in shell characters, and the differences in living animal morphology observed for Thai vs. Japanese specimens of S. violescens by Lützen and Nielsen (2005), the question arises whether more than one biological entity might be involved.

Irrespective of its unresolved specific affinity, the shell presented here clearly differs from all native Mediterranean galeommatids and thus cannot be confused; it can be easily distinguished from the non-indigneous Nudiscintilla cf. glabra (see above) by its less elongated shell, smaller L:H-ratio and, most notably, the presence of radial sculpture on the valves. Apart from the present shell, which was found in 1999 in Haifa Bay, we know of no other material.

Figures

Figure 41. Scintilla cf. violescens Kuroda & Taki, 1961, Haifa, Israel: right (A) and left (B) valve outer views, left (C) and right (D) valve inner views, hinge of left (E, G) and right (F, H) valve. Scale bars: 2 mm (A-D); 0.5 mm (E-H).