Specimens belonging to the complex of the striped false limpet Siphonaria pectinata (Linnaeus, 1758) sensu lato are marine gastropods of the family Siphonariidae Gray, 1827. They are characterized by an oval, limpet-like external shell with several radial brown stripes and a white to cream-tan color. Examined from above, the apex of their shells is slightly off-center, while the underside exhibits a C-shaped muscle scar (sometimes indistinct) opening to one side. Originally described from the Mediterranean Sea (see White and Dayrat, 2012), S. pectinata has been often considered to be distributed along the western and eastern Atlantic shores, with sporadic records from the western Pacific (e.g. Voss, 1959; Puizina et al., 2012 among others). However, Giribet and Kawauchi (2016) have recently shown that the former S. pectinata sensu auctores was a complex of three different species: S. naufragum Stearns, 1872, occurring in Florida and the Gulf of Mexico, S. placentula Menke, 1853, only known from the Cape Verde Archipelago, and S. pectinata, restricted to the eastern Atlantic up to Gabon and the Mediterranean Sea.
The known historical range of S. pectinata sensu stricto in the Mediterranean basin is unclear and widely debated. It included the Strait of Gibraltar, the African coastline up to Algeria (Monterosato, 1877, as Siphonaria algesirae; Pallary, 1900, as Siphonaria mouret) and the Spanish coastline up to Murcia/Valencia area (Hidalgo, 1917; Nicolay, 1980; Gofas, 2011), although its presence in wider areas has been often stated by other authors (see below). Unfortunately, the presence of unsubstantiated records in the old literature (usually from 1700 to around 1980) is well known to taxonomists and conservation biologists, and even some highly cited species in the literature may have never lived in the area where they have been (sometimes widely) recorded in the past. As an example, this may be the case of Locard (1886), who reported S. pectinata from the Mediterranean France (Port-Vendres), and later on Germain (1913) accepted that record while reviewing molluscan fauna from France. No recent records of S. pectinata from France exist, and previous records should be considered as doubtful. Another example is that of Pallary (1912), who recorded a Siphonaria sp. from Alexandria (Egypt), suggesting its possible identification as S. algesirae (= S. pectinata). However, the absence of Siphonaria material from the Pallary’s collection led Nicolay (1980) to conclude that it may have been most likely the alien Siphonaria laciniosa (Linnaeus, 1758), considered by the author as widespread along the eastern Mediterranean shores. Voss (1959) subsequently suggested an overall distribution of S. pectinata sensu lato limited by the 55 °F isocryme, and reported its presence in the Mediterranean from Spain up to Barcelona area and along the northern African shores up to Alexandria (Egypt). Few later, Morrison (1972) excluded its presence at the east of Algiers (Algeria), but did not discuss Pallary (1912) and Voss (1959) statements. No confirmed or recent records are known from the Mediterranean Sea east of Cap Bon area in Tunisia (see below), and the careful analysis of concrete materials from areas of original records may shed light on these questionable distribution data. On the contrary, among very recent confirmed records, Enzeroß and Enzeroß (2001) first recorded this species in Tunisia, soon followed by Antit et al. (2008). Siphonaria pectinata overall distribution in Tunisia seems to be now restricted to the country northern shores up to Cap Bon area (Enzeroß and Enzeroß, 2001; Antit et al., 2008; Tlig-Zouari et al., 2010; Boukhicha et al., 2015) but, as a matter of fact, known records from the area are all quite recent. Whilst Tunisian records seems to be more or less in continuity with the known historical distribution of the taxon, S. pectinata is also known in the Mediterranean Sea from two very distant geographic spots: the Saronikos Gulf (Greece), where its confirmed presence dates back >30 years (1979: Nicolay, 1980) and the Split area (Croatia), where its first record occurred in 2003 (Despalatović et al., 2008).
Records from these three latter countries have been widely discussed in the recent years, mostly due to uncertainties regarding possible rationale at the basis of the absence of past sightings. Range expansion from the nearby coastlines was originally suggested to explain its occurrence in Tunisia (Antit et al., 2008), although Gofas (2011) considered it later as “introduced”. Boukhicha et al. (2014) also listed it first among alien molluscs from Tunisia, but then considered it as a “non-native” species (Boukhicha et al., 2015), despite the fact that they considered it as arrived in Tunisia through a natural progression enhanced by climate change rather than a ship transport or other anthropogenic factors. Being “non-native” widely considered a synonym of “alien”, and therefore implying a human-mediated introduction (see Occhipinti-Ambrogi and Galil, 2004), the use of this term in defining this taxon seems inappropriate, at least in the context used by Boukhicha et al. (2015). Finally, Ounifi-Ben Amor et al. (2016) considered again Tunisian records as a range expansion. Several authors also concluded that the recent records from Greece (Gofas and Zenetos, 2003; Antit et al., 2008; Zenetos et al., 2010; Gofas, 2011; Boukhicha et al., 2015) and Croatia (Gofas and Zenetos, 2003; Antit et al., 2008; Despalatović et al., 2008; Zenetos et al., 2010; Puizina et al., 2012; Pećarević et al., 2013; Boukhicha et al., 2015; Marchini et al., 2015) may be the result of a human induced introduction rather than to a natural occurrence. As a matter of fact, the Cap Bon area (Strait of Sicily) constitutes a major hydrodynamical, biogeographical and geological transition zone within the Mediterranean Sea, and the major West–East transition zone (Bianchi, 2007; Azzurro et al., 2014). In addition, no fossil records are known from the European area, the species inhabits the intertidal attached to hard substrates, therefore suggesting its being easy to spot, and finally possesses a short larval stage (Ocana and Emson, 1999). To this, it should be added that historically known eastern Mediterranean populations, and even the recently discovered Tunisian one(s), are indeed too far away for natural range extension to operate for the Greek and Croatian records.
During my research on alien and native molluscan species in the Mediterranean Sea, I had the opportunity to analyze two potentially interesting S. pectinata lots from Croatia preserved in two Italian private collections. The aim of the present note is therefore to publish such distributional and temporal data as to backdate the first confirmed record of this taxon from Croatia and the northern Mediterranean shores, and to discuss its alien status sensu lato in the abovementioned countries in the light of the bibliographic researches held and the unpublished data reported herein.
