New species of Rissoidae (Mollusca, Gastropoda) from the Archipelago of the Azores (northeast Atlantic) with an updated regional checklist for the family

Abstract Four new species of shallow-water marine gastropods belonging to the family Rissoidae are described from the Archipelago of the Azores: Setia alexandrae sp. n., Setia ermelindoi sp. n., Setia netoae sp. n., and Manzonia martinsi sp. n. These novelties increase the regional rissoid fauna to 39 species, of which 29 live in shallow-water habitats. A list of the species of Rissoidae from the Azores is presented based on data from the literature and new material examined.

The genus Setia H. & A. Adams, 1852 is composed of minute gastropods with ovate to ovate-conic shells and convex whorls. The dome-shaped protoconch, having about 1.25 to 1.5 whorls, is smooth or possesses spiral rows of minute gemmae. The teleoconch is smooth or sculptured with weak to moderate spiral threads and axial growth lines. The aperture has a simple peristome.
There are 29 species of Setia in the Atlantic and the Mediterranean Sea (Ávila et al. 2012). With the exception of Setia triangularis (Watson, 1886) reported for the Caribbean and Ascension Island, all are shallow-water species. No species of this genus are reported for the Lusitanian seamounts (Gofas 2007). The Mediterranean Sea contains the largest number of species (18 species; 10 endemic), followed by the Canary Islands (7 species; 1 endemic), mainland Portugal (6 species), Archipelago of Madeira (4 species; 1 endemic), and the Azores (3 species; 2 endemic) (Ávila et al. 2012).
The genus Manzonia Brusina, 1870 is composed of minute gastropods with ovate-conic shells having robust axial sculpture formed by strongly curved to sinuous opisthocline ribs. The protoconch is multispiral (with netted microsculpture) or paucispiral (with gemmate or smooth spiral keels). The distinctive teleoconch microsculpture consists of a pitted surface on the flat spiral cords and very fine spiral threads in the interspaces between primary cords. The aperture is oval and the peristome is duplicated (Ponder 1985, Moolenbeek andFaber 1987).
A total of 24 species of Manzonia is present in the Atlantic and the Mediterranean Sea (Ávila et al. 2012). Of these, 6 are deep-water and 18 are shallow-water species. The deep-water species are restricted to the Lusitanian seamounts (Gofas 2007) and the West African coast (Gofas 2010). Twenty three of the 24 species are distributed in both the eastern Atlantic and the Mediterranean Sea. The remaining species, Manzonia epima (Dall & Simpson, 1901), is restricted to the western Atlantic. The Canary Islands (11 species; 3 endemic), Selvagens Islands (8 species; 1 endemic) and Archipelago of Madeira (7 species; 2 endemic) contain the largest numbers of species. The Archipelago of the Azores contains a single, endemic species (Ávila et al. 2012).
The present study describes three new species of Setia and a new species of Manzonia from the Archipelago of the Azores. A list of the species of Rissoidae from the Azores is presented based on data from the literature and new material examined.

Materials and methods
The specimens used in the present study were obtained from samples collected by about 850 dives and dredges in all islands of the Azores between the years 1967 and 2010. A total of 1,060 lots from the Mollusc Reference Collection of the Department of Biology of the University of the Azores (DBUA) were examined. During the course of examining the material, we found a total of 39,532 specimens of Rissoidae. All specimens were examined under stereomicroscope. The specimens in perfect conditions were selected as type material for the new species and measured with precision of 0.01 mm using a stereomicroscope with a digital camera coupled to a computer.
Living animals were photographed for observation of colour patterns. Shells were sonicated, coated with Au-Pd and then photographed with a Scanning Electron Microscope (SEM) for the study of the protoconch and teleoconch. Terminology adopted for shell descriptions follows Ponder (1985). A special focus was placed on protoconch and microsculpture as taxonomic characters at the species level. The suprageneric classification of Gastropoda is based on Bouchet and Rocroi (2005).
Habitat. On rocky shores covered by algae, from the intertidal down to 20 m depth. Geographical distribution. Pico, Graciosa, São Miguel and Santa Maria Islands, and Formigas Islets. Probably endemic to the Azores.
Habitat. On rocky shores covered by algae, from the intertidal down to 25 m depth. Geographical distribution. Flores, Pico and São Miguel Islands. Probably endemic to the Azores.
Habitat. On rocky shores covered by algae, from the intertidal down to 10 m depth. Geographical distribution. Flores, Graciosa and São Miguel Islands. Probably endemic to the Azores.
Remarks. This species appears to be uncommon on the Azorean shores. It differs from S. subvaricosa by lacking the vertical reddish flames on the shell that characterizes this species. It further differs from S. subvaricosa by the thinner outer lip of the aperture and by the absence of spiral threads on the protoconch. Setia netoae sp. n. differs from S. alexandrae sp. n. in having a more slender shell, 4 instead of 3 whorls on the teleoconch, by the distinctive colour pattern of the animal, and by the proportions of the last whorl/ total length of the shell, which are 60% versus 70-75%, respectively. Setia netoae sp. n. differs from other Atlantic congeners (cf. Ávila et al. 2012; and present study) by lacking the usual colourful patterns, such as wavy flames, blotches and lines, observed in the shells of this genus. It also has a more elongate shell than most of the known Setia. The shell resembles that of similar sized Setia antipolitana (van der Linden & Wagner, 1987), but the latter has vertical lines interrupted medially that are not present in S. netoae sp. n.   Figure 4 Type material. Holotype, DBUA 788 (sh., 1.75 × 1.13 mm); paratype 1, DBUA 1092 (sh., 1.88 × 1.20 mm); paratype 2, DBUA 1093 (sh., 1.76 × 1.14 mm); paratype 3, DBUA 1094 (sh., 1.72 × 1.10 mm); paratype 4, DBUA 1095 (sh., 1.76 × 1.06 mm), São Miguel Island (São Vicente Ferreira, 4.7 m depth, 16/07/1997).
Type locality. São Vicente Ferreira, São Miguel Island, Azores. Etymology. Named after António M. de Frias Martins, a malacologist from the University of the Azores.
Habitat. In the infralittoral on rocks covered by algae. Geographical distribution. São Miguel Island. Probably endemic to the Azores. Remarks. Manzonia martinsi sp. n. is similar in shell shape to Manzonia lusitanica Gofas, 2007 and Manzonia crispa (Watson, 1873). It differs from Manzonia lusitanica in having a lower number of spiral cords on the body whorl (9-10 in the new species and 12-13 in M. lusitanica). Manzonia martinsi sp. n. has 9-10 spiral cords on the body whorl and 4-6 raised spiral striae on the interspaces between cords, while M. crispa has 7 spiral cords on the body whorl and 8-10 lower spiral striae between cords. Manzonia martinsi sp. n. differs from M. arata Gofas, 2007 in the number of raised spiral striae on the interspaces as well as on the number of spiral lines with pits on the spiral cords, which are lower 2 to 3 times in the new species (Table 1).

Biodiversity and endemicity
The published information on the shallow-water rissoids of the Azores was compiled by Ávila (2000, 2005) and subsequently supplemented by Ávila et al. (2012), who analysed a revised and updated checklist with the entire Atlantic and Mediterranean rissoid fauna.
The Rissoidae is the most species-rich molluscan family in the Archipelago of the Azores. It also contains the largest number of endemic marine species in the region: 19 endemics (48.7%), if we consider all rissoids; or 15 (51.7%), if we consider only the 29 shallow-water species. All 19 Azorean endemic rissoids (15 shallow and 4 deep-water species) possess a non-planktotrophic mode of larval development.
The last account on the shallow-water marine molluscs from the Azores reports 423 taxa (Ávila, unpublished data), of which 6 are introduced species (Cardigos et al. 2006) and 34 are pelagic species. If these 40 species are discounted, there are 383 shallow-water benthic molluscs, of which 41 are endemic to the Azores (10.7% of endemisms). We note that the Rissoidae constitutes 36.6% of all endemic shallow-water benthic molluscs from the Azores, which further highlights the contribution of this family to regional biodiversity.