Iravadia aff. elongata (Hornung & Mermod, 1928)

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

Iravadia aff. elongata (Hornung & Mermod, 1928) Figure 13

New records.

Israel • 1 spcm; Ashqelon; 31.6868°N, 34.5516°E; depth 12 m; 30 Apr. 2018; offshore rocky reef; suction sampler; HELM project (sample S12_1F) • 5 shs; same collecting data as for preceding; depth 11 m; 31 Oct 2018; HELM project (sample S58_2F); size: H 2.8 mm, W 1.1 mm (largest (illustrated) shell).

Additional material examined.

Iravadia aff. elongata : Sudan • 2 shs; Arusa (near Port Sudan); 19.90°N, 37.23°E; shallow water; 1975; shell-grit; G. Spada leg.; MZUB.

Iravadia elongata (Hornung & Mermod, 1928): Eritrea • 1 sh; Massawa; depth 30 m; 1870; A. Issel leg.; syntype in MSNG; size: H 3.9 mm, W 1.4 mm.

Remarks.

This species is characterized by a turriform shell with up to five convex whorls, separated by a marked suture and a blunt, flat, and smooth protoconch. The sculpture consists of flat spiral ridges (12-14 on the penultimate whorl) that become more raised at both the adapical and abapical parts of the whorls, and which overlie numerous axial lines (Figure 13F ), resulting in a reticulate surface.

The closest match to our specimens is Iravadia elongata (Hornung & Mermod, 1928) which was described from material collected by Arturo Issel in the Red Sea off Massawa, Eritrea, at 30 m depth ( Hornung and Mermod 1928). Compared to our material, however, the syntype of I. elongata is larger (height 3.9 mm vs. 2.8 mm in our largest shell) and has seven less convex whorls. Further, the apical part of its spire has a slightly concave profile and thus appears more tapered. According to Issel’s description, the sculpture of I. elongata consists of spiral ridges (12 on the penultimate and 22 on the last whorl) as well as growth lines, although the latter are not indicated in the accompanying line drawing. This suggests that the axial component might be less evident in I. elongata than in our specimens, however, the poor preservation of the shell surface of the syntype of I. elongata did not allow a reliable comparison with our material. Slightly eroded shells very similar to our specimens have been collected from the Sudanese Red Sea (Figure 13G, H ), confirming that the material from Israel indeed represents an Indo-Pacific species rather than an undescribed Mediterranean taxon.

Among Mediterranean iravadiids, our specimens superficially resemble only Ceratia proxima (Forbes and Hanley, 1850). This species, however, lacks axial sculpture. Interestingly, Hornung and Mermod (1928) also mention the presence of this latter species at Assab (Eritrea) and “île Saldadin" (Zeila, northern Somalia). While obviously based on a misidentification - C. proxima has an Eastern Atlantic-Mediterranean distribution ( Bouchet and Warén 1993; Høisæter 2009) - one might speculate that this record could be the result of a confusion of C. proxima with the Iravadia presented here.

Figures

Figure 13. Iravadia aff. elongata (Hornung & Mermod, 1928) A-F Ashqelon, Israel, HELM project (sample S 58 _ 2 F): front (A, B) and back (C, D) views, protoconch (E) and detail of sculpture on the body whorl (F) G, H Arusa (near Port Sudan), Sudan: front view of an adult (G) and juvenile (H) shell. Scale bars: 1 mm (A-D, G, H); 0.2 mm (E); 0.3 mm (F).