Isognomon aff. australica (Reeve, 1858) (sensu Angelidis and Polyzoulis 2018)

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

Isognomon aff. australica (Reeve, 1858) (sensu Angelidis and Polyzoulis 2018) Figure 37

New records.

Cyprus • 1 sh; Turkish Republic of Northern Cyprus, Esentepe; 35.3589°N, 33.6078°E; depth 2 m; 28 Jul. 2019; rocky substrate; P.G. Albano leg. (sample NCY3H); size: L 11.8 mm, H 10.1 mm (Figure 37A, B, D, E ).

Greece • 1 spcm; Crete, Plakias; 35.1796°N, 24.3957°E; depth 5 m; 24 Sep. 2017; Posidonia oceanica rhizomes; suction sampler (sample Rh.05_4M); size: L 4.4 mm, H 4.4 mm (Figure 37C, F ).

Remarks.

The discrimination and identification of the species of Isognomon Lightfoot, 1786 is difficult due to their morphological plasticity that is related to their cryptic way of life. Still, the specimens recently reported from Astypalaia, in the Eastern Aegean Sea ( Lipej et al. 2017; Angelidis and Polyzoulis 2018), show clear morphological differences from I. legumen (Gmelin, 1791), the established non-indigenous species in the Mediterranean Sea: the main features of the sculpture are radial rather than concentric and the shape of the shell can be very elongated rather than subquadrate. We here report a juvenile living individual and an empty shell from Greece and Cyprus (for which this is a new record), respectively, which are not distinguishable from those previously reported from Astypalaia. Juvenile shells (up to a size of ~ 5 mm) bear a sculpture of radial ribs adorned by tubular spines. We do not comment upon the choice of the Isognomon australica name for this taxonomic entity by previous authors, lamenting the lack of a thorough revision of this genus in the Indo-Pacific province.

Figures

Figure 37. Isognomon aff. australica (Reeve, 1858) (sensu Angelidis and Polyzoulis 2018) A, B, D, E Esentepe, Cyprus (sample NCY 3 H): left valve outer (A) and inner (B) views, right valve inner (D) and outer (E) views C, F Plakias, Crete (sample Rh. 05 _ 4 M): left (C) and right (F) valve outer views. Scale bars: 2 mm.