Biodiversity Journal, 2019, 10 (4): 337–342 https://doi.org/10.31396/Biodiv.Jour.2019.10.4.337.342 The last alien reaching Sicily: Isognomon legumen (Gmelin, 1791) (Mollusca Bivalvia Isognomonidae) Danilo Scuderi1 & Alfio Viola2 1I.I.S.S. “E. Majorana”, via L. Capuana 36, 95048 Scordia, Catania, Italy: [email protected] 2Dipartimento di Scienze Biologiche, Geologiche ed Ambientali, Sezione di Scienze della Terra, Palazzo Ramondetta, Corso Italia 57, Catania, Italy; e-mail: [email protected] ABSTRACT The finding of some living specimens of an alien bivalve of the genus Isognomon Lightfoot, 1786 (Mollusca Bivalvia Isognomonidae) attached to rocks is here reported in Sicily for the first time. This is the last of a series of numerous finding of alien molluscs reports in the same area, for which a human-mediated model was supposed. An attempt to indicate the age of the specimens are here furnished on the basis of the number of byssus filaments. Some further environmental notes underline how in recent times these alien species seem better integrated inside the indigenous benthic communities in the Southern Mediterranean coasts, being better allowed in the first settlement by the recent climatic changes and resulting ecologically well organized and structured as in the tropical environments of provenance. KEY WORDS Alien species; Mediterranean; invasive species; Sicily; Bivalves; Mollusca; Isognomon. Received 13.09.2019; accepted 21.11.2019; published online 11.12.2019 INTRODUCTION ships, whose traffic is more increased today (Zibro- wius, 1992). Due to the high increased number of alien spe- In the Mediterranean Sea two species of Isogno- cies signalled in the Mediterranean Sea, in the last mon Lightfoot, 1786 (Mollusca Bivalvia Isogno- decades the tropicalization in marine environments monidae) are reported: I. legumen (Gmelin, 1791), seem to be a process less ethereal and more real which was firstly recorded and reported by Mienis than in the recent past. Findings of non-indigenous et al. (2016) from Israel, and I. australica (Reeve, mollusc species, like Pinctada radiata (Leach, 1858), reported by Angelidis & Polyzoulis (2018) 1814), started just after the Suez Canal aperture from Greece only in very recent times. (Monterosato, 1878). Nowadays, numerous records Despite its recent penetration, I. legumen concern in particular the eastern regions of the Me- seems on the contrary well distributed in the Me- diterranean, i.e., Lebanon, Israel, Turkey, Cyprus or diterranean Sea considering all the official records Egypt, being the first landing places for newcomer reported and those which could instead be consi- molluscs from the Red Sea. Another different way dered misidentifications with other species, i.e., is the human-mediated invasions, which seem to ju- Malleus regula (Forsskål in Niebuhr, 1775) (Bi- stify too rapid spreadings of alien species in those valvia Malleidae) (see for instances Crocetta, et regions far from the main Mediterranean entrances. al., 2017, and Stamouli et al., 2017, Crocetta, Among the latter, many are due to ballast waters of 2018). 338 DANILO SCUDERI & ALFIO VIOLA In Sicily, findings of human-mediated alien MATERIAL AND METHODS species have considerably intensified in these last two decades, with records of species which often The finding of a single specimen of I. legumen have been well established. The last in order of along the rocky shores of Catania, eastern Sicily (Fig. time is Lottia sp. (Scuderi & Eernisse, 2016), 1) in August 15, 2017 was rather fortuitous, since it whose complete identification and origin are still lied unattached on the rocky bottom at -1.5/2 m under study. depth. Probably during the night, fishes feed on the The discovery of seven living specimens and a mussel layer and detached it from the rocks. Two shell of the Bivalve I. legumen further updates the thorough samplings lead to the finding of other four number of alien species in central Mediterranean, spec. in the same season, which were handily re- adding new informations on the invasion modali- moved from the rocky substrates, at -1 to -4 m depth. ties and possibilities of establishment success of In summer (July/August) 2018 and 2019 four more the species inside the basin. This renovate the in- specimens were collected. In the same area and con- vocation to pay higher attention to ballast water, ditions in addition a complete sh. was found among whose management in Mediterranean Sea and not shell grit at -2 m depth. Mediterranean harbours should be regulated Shells were measured for morphological through stricter lows, which allowed limitations on analysis and the soft body was removed from the spreading of alloctons to different geographic each specimen’s shell and preserved in 90° sites. ethanol for future molecular analysis. Observa- ABBREVIATIONS AND ACRONYMS. h: tions were conducted with a stereoscope and pho- height; spec.: living specimens; sh.: shell/shells; st.: tographs and drawings documented the collected station; AGC: Alfio Germanà collection (Catania, specimens. Italy); PMC: Pasquale Micali collection (Fano, Pe- The Sicilian material was compared to speci- saro-Urbino, Italy); DSC: Danilo Scuderi collection mens collected in the Persian Gulf (PMC) and to (Scordia, Catania, Italy). specimens of I. australica from Karpatos, Greece, Figure 1. Map illustrating the collecting locality of Isognomon legumen in eastern Sicily (red spot). The last alien reaching Sicily: Isognomon legumen (Gmelin, 1791) (Mollusca Bivalvia Isognomonidae) 339 Figures 2–7. Isognomon legumen. Fig. 2: A specimen in upper view, Catania, eastern Sicily, h: 1.4 mm. Fig. 3, internal side of the left valve. Fig. 4: internal side of the right valve. Fig. 5: byssus. Fig. 6: specimen from Catania in upper view, h: 22.1 mm. Fig. 7: a pearl from a specimen from Catania, h: 1.2 mm. Figure 8. A living specimen in aquarium from Catania, h: 20.2 mm. Figures 9–12. Two specimens from Abu Dhabi, Persian Gulf, in upper and internal view with detail of the ligament, h: 31.2 and 42.0 mm respectively. Fig. 13. Isognomon australica, Karpatos, Greece, h: 3.4 mm. 340 DANILO SCUDERI & ALFIO VIOLA at -38 m depth, found in september/2017 (AGC) byssus to epibionts living on the volcanic substra- for supporting the morphological determination. tum, among the trottoir constituted by other mol- luscs, many of which were alien too, and red calcareous algae present in the subtidal zone. RESULTS Other species present were: Brachidontes pharao- nis (P. Fischer, 1870), Pinctada radiata (Leach, Systematics 1814), Ostrea stentina Payraudeau, 1826, Anomia ephippium Linnaeus, 1758, Mytylus galloprovin- Classis BIVALVIA Linnaeus, 1758 cialis Lamarck, 1819, Aplysia dactylomela Rang, Ordo OSTREIDA Férussac, 1822 1828. Superfamilia PTERIOIDEA Gray, 1847 Apart the first almost fortuitus record, among Familia ISOGNOMONIDAE Woodring, 1925 the algal turf and between the other epibionts pres- Genus Isognomon Lightfoot, 1786 ent and constituting a trottoir, specimens live col- Type species: Isognomon perna (Linnaeus, 1767) lected were easily detectable by the yellowish mantle seen between opened valves. Isognomon legumen (Gmelin, 1791) (Figs. 2–12) REMARKS. Isognomon legumen was often misidentified with Malleus regula (Crocetta, 2018), ExAMINED MATERIAL. Italy, Catania, eastern from which could be easily distinguished by the coast of Sicily, 9 spec. and 1 sh. along the northern edentuous hinge in which 5–6 peculiar resilifer rocky shore of the city, -1/4 m depth (DSC). Four bearing the ligament are present (Fig. 12). Being re- sh. of I. legumen from Abu Dhabi, United Arab cently penetrated in the Mediterranean, I australica Emirates (UAE), Persian Gulf, -3/6 m (PMC). (Fig. 13) is the most similar species in this basin. This latter has flat, almost smooth, except for some DESCRIPTION. Specimens collected were as- faint and flat axial ridges, fragile and semitranspar- signed to Isognomon on the basis of the character- ent valves, which make the species distinguishable istic “denticulate” ligament, being the hinge straight from I. legumen. Moreover, the niche they prefer is and edentulous (Figs. 3, 4 and 10–12). The height different: specimens of I. australica were collected of specimens varies from 22.6 to 14.8 mm. Valves attached with byssus under stones in the upper in- (Figs. 2–12) are variable in form, relatively solid fralittoral zone, preferring a slightly deeper fringe and moderately convex, rounded at margins except (Angelidis & Polyzoulis, 2018 and Micali pers. the upper side, which is straight, with a pointed lat- comm. feb/2019). erally placed umbo; they are ornamented by marked and fragile laminate processes, smooth and nacre- ous on the internal side (Figs. 2, 4 and 10, 11) and DISCUSSION AND CONCLUSIONS white-greenish in colour on the external side, with orange/yellowish periostracum. Harper & Morton (1994) reported the species Soft parts (Figs. 4 and 8) are pale green-yel- reaching a probable age of a couple of years, lowish with orange edges and gill tips of the man- which is therefore quick in growing, the age being tle; gonad is almost egg-yellow. Byssus is probably correlated to the number of filaments of constituted by numerous not very long green fila- the byssus as suggested by the same Authors. Sex- ments (Fig. 5). ual maturity seem reached just in specimens of 6 A single drop-shaped olive-green pearl (Fig. 7) mm (Harper & Morton, 1994): so all the Sicilian 1.2 mm high has been found inside a specimen. specimens were mature. They reported the most Specimens from