Rissoidae (Mollusca: Gastropoda) from northeast Atlantic seamounts

Abstract

The gastropod family Rissoidae is revised at the species level for the Lusitanian seamounts, situated between Portugal and Madeira, and the Meteor group of seamounts, situated south of the Azores in the northeast Atlantic Ocean. Based on material obtained by dredging and trawling, 48 species are reported, of which 30 are described as new. There is very little overlap between the assemblages found on both groups of seamounts, with only two shared species. On the Lusitanian seamounts, 24 species were collected. Seven species (six with planktotrophic development) are shared with the mainland shelf or slope and are represented in low numbers. Eleven species are endemic to this seamount group as a whole and of these, three account for 75% of individuals. Of the species not shared with the mainland, only one is found on the four seamounts, eight (three new) are found on two or three seamounts and/or neighbouring islands, and six (all new) are endemic to a single seamount. On the Meteor group, 26 species were found, of which five are shared with the Azores and 20 (all new) are endemic to the seamount group as a whole. Most species are found on only two or three seamounts, whereas nine species are endemic to only one of the seamounts, and of these five are concentrated on Atlantis seamount. Eight endemic species of the Meteor group included in Porosalvania n. gen. have very different shapes and occupy discrete bathymetric intervals, but are best interpreted as a local radiation originating from a relatively old colonization of this seamount group. The endemic species, and among them the successful ones, all have a paucispiral protoconch denoting non-planktotrophic development. As in the Macaronesian archipelagos, the Rissoidae are the most species-rich molluscan family on the northeast Atlantic seamounts.

Gold coral (Savalia savaglia) and gorgonian forests enhance benthic biodiversity and ecosystem functioning in the mesophotic zone

“…On the other hand, other species typically observed in epi-bathyal sediments (such as the rissoid Alvania punctura Montagu 1803, and Alvania zetlandica Montagu 1815, and the epitoniid Epitonium tiberii (De Boury 1890) reached their shallower limit (Bouchet and Warén 1986;Giribet and Peñas 1997;Gofas 2007) inside the gold coral forest. Amongst bivalves, the record of Limopsis minuta (Philippi 1836) in the thanatocoenosis can be considered another example of shallower occurrence of a species which usually occurs from 300 to more than 1500 m depth (Salas, 1996).…”

New Cheilostomata (Bryozoa) from NE Atlantic seamounts, islands, and the continental slope: evidence for deep-sea endemism

“…Results of studies of particular taxonomic groups or community assemblages from seamounts are contrasted in terms of the geographical range of species: a particularly high proportion of endemics is revealed by some of them (e.g., Richer de Forges et al 2000;George & Schminke 2002;Gofas 2007;McClain et al 2009) while, in contrast, other studies show a lack of endemism within seamount assemblages (e.g., Samadi et al 2006;Thoma et al 2009). The set of bryozoan species described here provides a striking example of endemism linked to geographic isolation between the various seamounts, islands and sites from the bathyal continental slope.…”

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

“…Such gastropods are also very abundant in the northeast Atlantic seamounts (Ávila and Malaquias 2003, Ávila et al 2004, 2007, Gofas 2007) as well as in the Archipelago of the Azores (Dautzenberg 1889, Aartsen 1982, Amati 1987, Moolenbeek and Faber 1987, Gofas 1989, 1990, Bouchet and Warén 1993, Hoenselaar and Goud 1998, Ávila 2000, Costa and Ávila 2001, Martins et al 2009), Madeira, Porto Santo and Desertas Islands (Manzoni 1868a, 1868b, Watson 1873, Nobre 1937, Moolenbeek and Faber 1987, Moolenbeek and Hoenselaar 1989, 1998, Hoenselaar and Goud 1998, Segers et al 2009), Selvagens Islands (Albuquerque et al 2009), Canary Islands (Rolán 1987, Verduin 1988, Moolenbeek and Hoenselaar 1989, 1992, 1998, Hernández-Otero and García 2003) and Archipelago of Cape Verde (Rolán 1987, Moolenbeek and Rolán 1988, Templado and Rolán 1993, Rolán and Rubio 1999, Rolán and Luque 2000, Rolán 2005, Rolán and Oliveira 2008). …”

“…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).…”