Cerithiopsis, Forbes and Hanley, 1850

Romani, Luigi, Rolán, Emilio, Mifsud, Constantine & Crocetta, Fabio, 2017, Redescription of Retilaskeya horrida (di Monterosato, 1874) comb. nov. and a re-evaluation of the taxonomic affinity of the genus Retilaskeya (Caenogastropoda: Triphoroidea), Journal of Natural History 52 (1 - 2), pp. 115-135 : 127-128

‘ Cerithiopsis ’ horrida generic replacement

As stated above, observations reported in the present paper highlighted strong morphological and radular similarities between ‘ Cerithiopsis ’ horrida di Monterosato, 1874 and species belonging to the genus Retilaskeya Marshall, 1978 (see Table 1 for details), as hinted at by Marshall (1978) based on Nordsieck’ s (1968) misidentified C. horrida specimens. In particular, the radula observed here in ‘ Cerithiopsis ’ horrida clearly belongs to the Eumetula -group radular type, quite different from the Cerithiopsis -group radular type (both sensu Nützel 1998), which includes the Cerithiopsis tubercularis complex. In fact, the latter species possess long and ribbon-like teeth with elongated and ‘hair-like’ cusps, referred to as ‘spaghettiradula’ ( Fretter 1951; Nützel 1998). Although it may be argued that similar shell morphologies may result from convergence and that radular diversity may be based on host-specific adaptation, such a combination of different characters appearing in a number of worldwide species suggests they are truly diagnostic features, as treated in the current literature.

Thus far, Retilaskeya includes six valid species, occurring both in the Pacific Ocean [ Retilaskeya elegantula (Powell, 1930) , Retilaskeya zelandica Marshall, 1978 , Retilaskeya philippinensis Cecalupo and Perugia, 2012 , and Retilaskeya rufocincta Cecalupo and Perugia, 2013 ] and the western Atlantic Ocean [ Retilaskeya emersonii (C.B. Adams, 1839) and Retilaskeya bicolor (C.B. Adams, 1845) ] ( Marshall and Bouchet 2015b). However, this assortment is not without its problems. As for shell morphology, the four Pacific species of Retilaskeya seem to be also closely related to Seila chenui Jay and Drivas, 2002 and Seila reunionensis Jay and Drivas, 2002 from Reunion Island (Indian Ocean). All these taxa listed above share protoconch features with Retilaskeya type species ( R. zelandica ), but differ in teleoconch features (anterior canal twisted and different sculpture, with spiral cords predominating, cords 1 and 3 starting immediately and cord 2 subsequently). On the other hand, Cecalupo and Perugia (2014) recently suggested the reassignment of S. reunionensis to Cerithiella Verrill, 1882 , although shell features of this taxon differ from typical Cerithiella taxa in protoconch and teleoconch sculpture (see Bouchet and Warén 1993; Fernandes et al. 2015). This might be also based on the fact that the specimen from Madagascar examined by Cecalupo and Perugia (2014) may not be conspecific with S. reunionensis (spiral threads distributed all over the protoconch whorls and slightly different teleoconch sculpture and shell outline). On the other hand, the two western Atlantic species of Retilaskeya form a morphologically homogeneous group with the Panamic Eumetula intercalaris ( Carpenter, 1865) and Eumetula bimarginata (C.B. Adams, 1852) , as observed by García (2009). A further taxon belonging to the same group of species may be the ‘Cerithiidae’ from off Chile reported and figured by Romero and Valdebenito (2002, figure 3). It is finally noteworthy to mention here that a further species originally described from São Tomé Island ( Cape Verde), namely Cerithiopsis leopardus Rolán and Gori, 2013 , seems also to overall belong to the Retilaskeya lineage: it has a teleoconch almost identical to ‘ Cerithiopsis ’ horrida , only showing small differences in protoconch features, with a protoconch–teleoconch transition even less defined, a nucleus not distinctly granulate, fewer and more raised axial ribs, and weaker and irregular spiral threads (Rolán and Gori 2013).

Indeed, it is highly improbable that all these species belong to a single genus, due to morphological and biogeographic reasons. However, based on present observations, we suspect that they may all belong to a single phylogenetic lineage, until now considered to be absent from the north-eastern Atlantic/Mediterranean. Taking into account the proliferation of new genera within Cerithiopsidae H. Adams and A. Adams, 1853 , as well as the wide uncertainties in supraspecific assignments reported above, we here refrain to assign ‘ Cerithiopsis ’ horrida to a new genus based on biogeographical support only. For sake of homogenization, and pending a combined approach including molecular tools, we provisionally suggest transferring ‘ Cerithiopsis ’ horrida to Retilaskeya , the earliest available genus-level taxon for this group of species, based on shell and radular features ( Retilaskeya horrida comb. nov.). The same presumably holds true for its possible sister species ‘ Cerithiopsis ’ leopardus ( Retilaskeya leopardus comb. nov.), although attempts to extract radulae from living specimens have failed so far.