PHILINIDAE, GRAY, 1827

DIVERSITY OF PHILINIDAE View in CoL S. L. IN WEST AFRICA

The Philinidae View in CoL snails were recently the focus of several taxonomic studies that have used characters other than the shell. A common denominator to all these works was the discovery of cryptic diversity; for example, Price et al. (2011) addressed the systematics of the Indo-Pacific Philine aperta View in CoL species-complex and described four new species; Ohnheiser & Malaquias (2013) in a study focused on the Scandinavian fauna described two new species; and Gonzales & Gosliner (2014) added six new lineages to the tropical Indo-Pacific fauna mainly from deep waters. Caballer & Ortea (2015) described the second species of Spiniphiline View in CoL from the western Atlantic, and Oskars et al. (2015) unravelled the complex phylogenetic relationships of philinid snails and hinted the occurrence of a multitude of undescribed species in the Indo-Pacific, most of them from the deep sea (T. R. Oskars & M. A. E. Malaquias, unpublished data).

Before the present contribution, 15 species of philinids were known in West Africa, five of which resulted from the work of van der Linden (1995) alone and were described based on shells only (see Table 1). van der Linden (1995) referred to the possible occurrence of an additional species – P. ventricosa View in CoL – but he cast doubt on the identity of the single juvenile damaged shell collected at 420 m depth off S ao ~ Tiago Island, Cape Verde, and therefore we disregard the occurrence of this species in West Africa until sound evidence is available.

In the present monograph, we refer to an additional putative five new species, four of which are here formally described ( P. cerebralis sp. nov., L. nanseni sp. nov., P. schrammi sp. nov., Philine sp. , Spiniphiline caboverdensis sp. nov.) and we provide the first data on the occurrence of the genus Spiniphiline in the eastern Atlantic Ocean. This raises the number of known and named species of Philinidae s.l. in West Africa to 19.

Price et al. (2011) have reinstated the name P. quadripartita for the white and large Atlantic philinid form, broadly named by authors as P. aperta (e.g. Thompson, 1988; Poppe & Goto, 1991; Cervera et al., 2004). Similarly, in this work we also provide evidence for the existence of a complex of at least four species that have been reported under the name P. quadripartita in the eastern Atlantic Ocean. Beside the latter species, our results confirmed the taxonomic validity of P. guineensis (originally described as P. aperta guineensis ) and have unravelled the existence of two additional lineages; one of them is formally described here as P. schrammi sp. nov. All these species are indistinguishable by their external morphology, but show subtle differences in their anatomy, mostly in the shape of the gizzard plates and in male reproductive system (see Remarks sections of these species).

BIOGEOGRAPHY OF WEST AFRICAN PHILINIDS

A striking biogeographical break was observed around Cape Verde and the Sahelian upwelling system between Mauritania and Guinea Bissau. This coincides with a classical transition zone between the northern cold-temperate fauna of the Lusitanian (including the Canaries, Azores and Madeira archipelagos) and northern European seas provinces and a more southern fauna inhabiting the Tropical Eastern Atlantic/Gulf of Guinea Provinces (the WAT sensu Spalding et al., 2007; Briggs & Bowen, 2012).

Of the 19 named species of Philinidae in West Africa, eight have their northern geographical range in this area or are geographically restricted to the WAT Province, and ten species have their southern limit here or just further north ( Fig. 15 View Figure 15 ; see Table 1 for detailed distributions of species). Only P. scabra seems to span across this biogeographical break point ( Fig. 15 View Figure 15 ). Nevertheless, as pointed out in the Remarks section for P. cerebralis sp. nov. (Taxonomic Results), the previous use of the name P. scabra for West African specimens might result from a misidentification as the shells of the latter two species are nearly indistinguishable. Likewise, the citations of P. quadripartita south of Morocco are doubtful, as they probably refer to one of its southern cryptic species described in this work.

Garc � ıa & Bertsch (2009) have suggested a similar discontinuity for the ‘opisthobranch’ gastropods in general (sensu Burn & Thompson, 1998). The authors have found a break roughly in this same area separating a predominantly Atlanto-Mediterranean fauna confined southwards by the cold-temperate Canary current (Artic and Temperate Northern Atlantic realms; sensu Spalding et al., 2007) with an apparent limited capacity to extend into warm waters, and a southern fauna restricted in the north by the warm Senegalese waters and in the south by the cold waters of the Benguela current .