Siboga, Hampson, 1901

Criscione, Francesco, Hallan, Anders, Puillandre, Nicolas & Fedosov, Alexander, 2021, Where the snails have no name: a molecular phylogeny of Raphitomidae (Neogastropoda: Conoidea) uncovers vast unexplored diversity in the deep seas of temperate southern and eastern Australia, Zoological Journal of the Linnean Society 191, pp. 961-1000 : 961-963

Albatross and Siboga ( Watson, 1886; Dall, 1908;

Schepman, 1913), deep-sea exploration remains one of the major frontiers for the discovery of marine mollusc biodiversity ( Bouchet et al., 2016). During the last 35 years, deep-sea expeditions have been conducted across the Indo-Pacific under the Tropical Deep-Sea Benthos (TDSB) programme, led by the Muséum national d’Histoire naturelle (MNHN) (https:// expeditions.mnhn.fr). These expeditions have revealed a significant molluscan diversity, roughly projected to be in the order of 25 000–30 000 species for the south Pacific ( Bouchet et al., 2008). An estimated 5000 of these comprise the group commonly referred to as turriform conoidean gastropods. Turriform Conoidea , or simply ‘turrids’, is a conventional name used for the heterogenous assemblage including all but two ( Conidae and Terebridae ) of the 18 currently recognized families in the neogastropod superfamily Conoidea Fleming, 1822 ( Bouchet et al., 2009; Abdelkrim et al., 2018a). Turriform Conoidea is the most diverse group of marine molluscs, with current estimates of 354 valid extant genera and 3776 named extant species (WoRMS Editorial Board, 2020). Maximum species diversity within ‘turrids’ is found in offshore and deep-sea gastropod assemblages, but many species have low abundance ( Sysoev, 1997; Kantor et al., 2008; Bouchet et al., 2009). In general, turriform conoideans are characterized by considerable morphological homoplasy, with numerous cases where distantly related taxa exhibit almost identical shell shape and sculpture ( Sysoev, 1997; Kantor et al., 2008; Bouchet et al., 2009).

Because of their high diversity, low abundance and morphological complexity, the systematics of deepsea turriform conoideans below the level of family remains tentative. Genera and species are diagnosed primarily based on morphology (e.g. Bouchet & Warén, 1980; Sysoev & Kantor, 1990; Sysoev, 1996a, b, 1997; Bouchet & Sysoev, 2001; Sysoev & Bouchet, 2001) and comparatively few genetic studies are available (e.g. Puillandre et al., 2009, 2010; Fedosov & Puillandre, 2012; Kantor et al. 2012, 2016, 2018; Abdelkrim et al., 2018b; Fassio et al. 2019; Hallan et al., 2020). These studies challenged current species delimitations and highlighted pervasive genus-level paraphyly (e.g. Bouchet & Warén, 1980; Sysoev & Kantor, 1990; Sysoev, 1996 a, 1996b, 1997; Bouchet & Sysoev, 2001; Sysoev & Bouchet, 2001; Puillandre et al., 2010; Kantor et al., 2018). Furthermore, a comparatively large proportion of deep-sea turriform conoideans still await description. For many areas, the number of undescribed species far outnumbers that of described species. For instance, it has been estimated that in New Caledonia, about 80% of deep-sea turriform conoideans are undescribed ( Bouchet et al., 2008).

The family Raphitomidae Bellardi, 1875 ( Bouchet et al., 2011), notably occurs in the deep sea and is among the most poorly studied families of the group ( Bouchet et al., 2011). The family comprises a total of 795 extant accepted species in 65 extant accepted genera (WoRMS Editorial Board, 2020). Nearly twothirds of these genera (39), accounting for more than half of the overall raphitomid diversity (418 species), are found below the continental shelf. These figures are based on the notion that bathymetric preferences of turriform conoidean genera are exclusive of either deep or shallow seas ( Bouchet et al., 2009). The type species of almost half of the deep-sea raphitomid genera were described in the 19 th century, with only four named post-2000. No molecular data have accompanied these descriptions, and anatomical data were provided only occasionally (e.g. Sysoev & Kantor, 1986; Sysoev, 1988; Kantor & Sysoev, 1989; Sysoev & Bouchet, 2001). For the vast majority of these genera, shell features are the only source of taxonomic information accessible from their type species. In addition, descriptions of most deep-sea raphitomid species have been provided in faunistic studies, aiming primarily to present the results of sampling campaigns in a given region and not necessarily to resolve the systematics. Consequently, generic attributions have been almost exclusively based on shell features and are, therefore, influenced by problems with character interpretation and undetected homoplasies. This issue has resulted in the current situation whereby only three genera encompass approximately half of all accepted deep-sea raphitomid species. These genera ( Gymnobela Verril, 1884: 75 spp. ; Pleurotomella Verril, 1872: 100 species ; and Xanthodaphne Powell, 1942: 33 spp. ) have subsequently been colloquially addressed as ‘dumpsters’, acting as provisional containers for newly described species of problematic generic attribution. For instance, Sysoev & Bouchet (2001: 305) state: ‘we somewhat arbitrarily include the yoshidai complex of species in Gymnobela ’.

Among the consequences of such unresolved systematics is a tentative status of the current biogeography of deep-sea raphitomids. A search of the Global Biodiversity Information Facility (GBIF – https://www.gbif.org) for the eight most speciesrich genera (> 10 species), reveals that they all occur outside the marine realm for which their type species was described. Most are found in several of the 30 marine realms [as delimited in Costello et al. (2017)]: Pleurotomella and Gymnobela occur in 18 and 19 realms, respectively, Phymorhynchus Dall, 1908 and Taranis Jeffreys, 1870 occur in 15 realms, Xanthodaphne in 11 and Nepotilla Hedley, 1918 in seven.

However, without adequate phylogenetic evidence, monophyly of genera cannot be assessed, thus preventing appropriate biogeographical investigation. Assumptions of wide distributions of genera, as currently accepted, would be upheld only in a scenario where their monophyly is confirmed. However, large distributions of single genera are currently considered rare ( Sigwart et al., 2017). In an alternative scenario, any notion of wide distributions would be an artefact of genus paraphyly.

There has been no recent attempt to revise the systematics and biogeography of any deep-sea raphitomid genus. However, this is now possible for the Raphitomidae of southern and south-eastern Australia, since suitable material has become available as a result of a number of expeditions aiming to quantify slope and abyssal biodiversity of the area ( Fig. 1) ( MacIntosh et al., 2018; Williams, 2018; O’Hara et al., unpublished data). These surveys have yielded a considerable amount of well-preserved gastropod material from depths ranging between approximately 900 and 5000 m. Our preliminary identification of this material has revealed a predominant raphitomid component, consisting almost exclusively of undescribed taxa.

The present study combines morphological and molecular evidence generated from this newly available material in order to construct a robust phylogenetic framework with the aim to:

1. Reconstruct the phylogeny of Australian deep-sea Raphitomidae , with inclusion of taxa from adjacent regions, whenever possible and appropriate.

2. Delimit and describe new deep-sea raphitomid genera from southern and eastern Australia, to facilitate subsequent taxonomic revisions.

3. Explore the biogeographic patterns of the raphitomid fauna in the area and (when possible) compare these with those observed in other adjacent marine regions.