Musculus aff. viridulus (H. Adams, 1871)

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

Musculus aff. viridulus (H. Adams, 1871) Figure 36A-E

New records.

Israel • 1 spcm; Ashqelon; 31.6891°N, 34.5257°E; depth 25 m; 2 May 2018; offshore rocky reef; suction sampler; HELM project (sample S16_2F) • 15 spcms; same collecting data as for preceding; depth 28 m; 31 Oct. 2018; HELM project (samples S59_1F, S59_1M, S59_2F, S59_2M) • 2 spcms; west of Rosh HaNikra Islands; 33.0704°N, 35.0926°E; depth 12 m; 1 May 2018; rocky substrate; suction sampler; HELM project (samples S14_3F, S14_4M) • 25 spcms; same collecting data as for preceding; 29 Oct. 2018; HELM project (samples S52_1F, S52_2F, S52_2M, S52_2L, S52_3F, S52_3M, S52_3L); size: L 3.6 mm, H 2.1 mm (illustrated specimen, Figure 36A-E ) • 1 spcm; west of Rosh HaNikra Islands; 33.0725°N, 35.0923°E; depth 20 m; 1 May 2018; rocky substrate; suction sampler; HELM project (sample S13_3M) • 9 spcms; same collecting data as for preceding; depth 19 m; 29 Oct. 2018; HELM project (samples S53_1F, S53_2F, S53_2M, S53_3F, S53_3M).

Additional material examined.

Musculus aff. viridulus : Egypt • 1 v; Sinai (Red Sea), Dahab, dive site “Caves”; 28.416°N, 34.456°E; depth 15 m; 2015; H. Blatterer leg. • 4 vv; same collecting data as for preceding; depth 17-19 m; 2016; H. Blatterer leg. • 2 vv; same collecting data as for preceding; depth 18 m; 2017; H. Blatterer leg. • 1 v; Sinai (Red Sea), Dahab, dive site "Golden Blocks"; 28.436°N, 34.459°E; depth 18 m; 2018; H. Blatterer leg.

Musculus costulatus (Risso, 1826): Israel • 9 spcms, 4 vv; Ashqelon; 31.6868°N, 34.5516°E; depth 12 m; 30 Apr. 2018; offshore rocky reef; suction sampler; HELM project (samples S12_1F, S12_1M, S12_1L, S12_2F, S12_2M) • 3 spcms; Ashqelon; 31.6891°N, 34.5257°E; depth 25 m; 2 May 2018; offshore rocky reef; suction sampler; HELM project (samples S16_1F, S16_2F) • 1 spcm; same collecting data as for preceding; depth 28 m; 31 Oct. 2018; HELM project (sample S59_1M) • 5 spcms; west of Rosh HaNikra Islands; 33.0704°N, 35.0926°E; depth 12 m; 1 May 2018; rocky substrate; suction sampler; HELM project (samples S14_1L, S14_3F, S14_3L, S14_4F) • 56 spcms; same collecting data as for preceding; 29 Oct. 2018; HELM project (samples S52_1F, S52_1M, S52_1L, S52_2F, S52_2M, S52_2L, S52_3F, S52_3M, S52_3L) • 1 v; west of Rosh HaNikra Islands; 33.0725°N, 35.0923°E; depth 20 m; 1 May 2018; rocky substrate; suction sampler; HELM project (sample S13_3F) • 20 spcms; same collecting data as for preceding; depth 19 m; 29 Oct. 2018; HELM project (sample S53_2L).

Remarks.

We report numerous living individuals of Musculus aff. viridulus from the Mediterranean Israeli coastline. It is the first record of this Indo-Pacific species in the Mediterranean Sea. This species can be readily distinguished from the native M. costulatus because the latter has a more oval outline and a much smaller number of riblets at the same overall shell size (Figure 36 ). These riblets are also much larger compared to M. aff. viridulus . The Atlanto-Mediterranean M. discors (Linnaeus, 1767) has a similarly fine posterior sculpture but at the same size is much higher and at all sizes bears much more prominent riblets anteriorly. The taxonomy of Musculus in the Indo-Pacific province is not settled and the available images of Red Sea M. viridulus ( Oliver 1992; Zuschin and Oliver 2003) show a more oval species, hence our dubitative identification. Still, we are confident that this is a Red Sea species because we examined indistinguishable specimens from the northern Red Sea (Figure 36F-H ). Blatterer (2019) illustrated these and other similar specimens (plate 10, fig. 18a, b) as Gregariella ehrenbergi (Issel, 1869). We recorded a morphologically distinct species as G. ehrenbergi from a buoy stranded on the Israeli coastline ( Steger et al. 2018; Ivkić et al. 2019). Gregariella ehrenbergi type material is corroded by Byne’s disease and the original description likely refers to a juvenile specimen; the identity of this species deserves further scrutiny.

Figures

Figure 36. Comparison between Musculus aff. viridulus (H. Adams, 1871) and Musculus costulatus (Risso, 1826) A-E Musculus aff. viridulus, west of Rosh HaNikra Islands, Israel, HELM project (sample S 52 _ 3 L): left valve outer (A, B) and inner (D) views, right valve inner (C) and outer (E) views F-H Musculus aff. viridulus, dive site " Caves ", Dahab, Sinai, Egypt: left valve outer (F, G) and inner (H) views I-M Musculus costulatus, west of Rosh HaNikra Islands, Israel, HELM project (sample S 53 _ 2 L): left valve outer (I, J) and inner (L) views, right valve inner (K) and outer (M) views. Scale bars: 1 mm.