European Journal of Taxonomy 12: 1-24 ISSN 2118-9773 http://dx.doi.org/10.5852/ejt.2012.12 www.europeanjournaloftaxonomy.eu 2012 · P. Graham Oliver This work is licensed under a Creative Commons Attribution 3.0 License. Research article Taxonomy of some Galeommatoidea (Mollusca, Bivalvia) associated with deep-sea echinoids: A reassessment of the bivalve genera Axinodon Verrill & Bush, 1898 and Kelliola Dall, 1899 with descriptions of new genera Syssitomya gen. nov. and Ptilomyax gen. nov. P. Graham OLIVER Dept. of Biodiversity & Systematic Biology, National Museum of Wales, Cathays Park, Cardiff, Wales, UK. E-mail: [email protected] Abstract. The type species of Axinodon ellipticus Verrill & Bush, 1898 and Kellia symmetros Jeffreys, 1876 are re-described. It is concluded that the two species are not conspecifi c and that K. symmetros cannot be placed in the genus Axinodon. The family affi nity of Axinodon is not resolved, although it is probable that this genus belongs to the Thyasiridae. Kellia symmetros is the type species of Kelliola and is placed in the Montacutidae. Kelliola symmetros is most probably associated with the echinoid Aeropsis rostrata and is not the species previously recorded from North Atlantic Pourtalesia echinoids under the name of Axinodon symmetros. This commensal associated with the North Atlantic Pourtalesia is here described as new and placed in the new genus as Syssitomya pourtalesiana gen. nov. sp. nov., Syssitomya gen. nov. differs from all other genera in the Montacutidae by having laminar gill fi laments modifi ed for harbouring symbiotic bacteria and it is thus assumed to be chemosymbiotic. A montacutid associated with the hadal Pourtalesia heptneri is described as Ptilomyax hadalis gen. nov. sp. nov. Key words. Galeommatoidea, deep-sea, echinoids, commensal, new genera. Oliver P.G. 2012. Taxonomy of some Galeommatoidea (Mollusca, Bivalvia) associated with deep-sea echinoids: A reassessment of the bivalve genera Axinodon Verrill & Bush, 1898 and Kelliola Dall, 1899 with descriptions of new genera Syssitomya gen. nov. and Ptilomyax gen. nov. European Journal of Taxonomy 12: 1-24. http://dx.doi. org/10.5852/ejt.2012.12. Introduction The bivalve currently known as Axinodon symmetros (Jeffreys, 1876), a commensal associated with the deep-sea echinoid Pourtalesia A. Agassiz, 1869, has been found to have a gill structure similar to that of the Thyasiridae Dall, 1900, and to harbour symbiotic bacteria suggesting that it may be chemosymbiotic (Oliver, Southward & Dando in press). In that study, some key taxonomic issues arose that now require resolution before publication of that study can proceed. 1 European Journal of Taxonomy 12: 1-24 (2012) Firstly, there has been debate about the family placement of Axinodon Verrill & Bush, 1898. Originally, it was placed in the Thyasiridae (Verrill & Bush 1898) and this was followed by Aartsen (1996) and Coan et al. (2000). Ockelmann (1965) placed it in the superfamily Galeommatoidea Gray, 1840 and family Montacutidae Clark, 1855; this placement was maintained by Chavan (1969) and is followed in the current European checklist (CLEMAM 2012). The implications of this debate are twofold: • If Axinodon were a thyasirid then the chemosymbiosis might be expected, but the commensalism would be a fi rst for that family. • If Axinodon were a montacutid then Axinodon would be the fi rst of that family and the fi rst commensal bivalve shown to harbour symbiotic bacteria. Secondly, it was also discovered that commensal bivalves were present on the echinoid Aeropsis rostrata (Wyville Thomson, 1877), but although similar to that on Pourtalesia, they were not identical. Eve Southward (pers. comm.) noted that the type locality and sample number for Aeropsis rostrata is the same as that for Kellia symmetros Jeffreys, 1876, both from “Station 9” of the “Valorous Expedition” in the Davis Straits. This brought into question the identity of K. symmetros and the identity of the Pourtalesia commensal. This is further exacerbated by the confl icting descriptions of Axinodon, some stating that it is edentulous (Aartsen 1996) other showing a distinct tooth in the right valve (Bouchet & Warén 1979). Bivalves belonging to the Galeommatoidea and the Montacutidae in particular have long been known to be commensal with species of sea-urchins and some shallow water species have been studied in considerable detail. There are numerous family and subfamily taxa proposed within the Galeommatoidea (Bieler & Mikkelsen 2006) but their distinction and relationships remain controversial (Mikkelsen & Bieler 2007) although the latter authors do recognise the Galeommatidae Gray, 1840 as distinct form all others. Mikkelsen & Bieler (2007) and Carter et al. (2011) refer all non-galeommatids to the Lasaeidae Gray, 1842, that being the earliest family name. Many other authors continue to follow the classifi cation of Chavan (1969) and adopt Montacutidae Clark, 1855 for those taxa morphologically similar to Montacuta Turton, 1822 (Jespersen et al. 2004; Kamenev 2008; Gofas & Salas 2008). Jespersen et al. (2004) argue for recognition of Montacutidae on grounds of hinge and anatomical characters in that the Lasaeidae, Leptonidae and Kelliidae have both cardinal and lateral teeth, and the presence of dimorphic sperm is peculiar to species placed in the Montacutidae. Unfortunately, galeommatoids are poorly represented in molecular phylogenies (Taylor et al. 2007) and there is no resolution at the family level. Here, Montacutidae is preferred over Lasaeidae, as the species under consideration are morphologically most similar to Montacuta and other associated genera that have been grouped in the Montacutidae. Popham (1940) and Oldfi eld (1961) studied the morphology of Montacuta substriata (Montagu, 1808) [associated with Spatangus purpureus (Müller, 1776)] and Tellimya ferruginosa (Montagu, 1808) [associated with Echinocardium cordatum (Pennant, 1777)]. Gage (1966 a, b, c) studied the behaviour of these species. Ockelmann (1965) studied Montacuta (Decipula) tenella (Lovén, 1846) [now Tellimya tenella (Lovén, 1846)] associated with Brissopsis lyrifera (Forbes, 1841). From South- east Asia, Jespersen, Lützen & Nielsen (2004) studied the fi ne anatomy of three species all associated with Brissus latecarinatus (Leske, 1778) and created two new genera Montacutella Jespersen, Lützen & Nielsen, 2004 and Brachiomya Jespersen, Lützen & Nielsen, 2004. Table 1 gives a compilation of galeommatids known to be commensal with echinoids. Associations with deep-sea echinoids are known, but taxonomic recognition has been restricted to a single taxon associated with North Atlantic species of Pourtalesia. Currently this taxon is known as 2 OLIVER P.G., Galeommatid bivalves from deep-sea echinoids Table 1. Galeommatoid species attached toT or associated withW echinoids Reference to Galeommatoid Associated echinoid Distribution Depth range association WTellimya ferruginosa Echinocardium cordatum Gage 1966a; Intertidal NE Atlantic (Montagu 1808). (Pennant, 1777) Oldfi eld 1961 Shelf WTellimya tenella Brissopsis lyrifera Ockelmann 1965 NE Atlantic Shelf (Lovén, 1846) (Forbes, 1841) TMontacuta substriata Spatangus purpureus Gage 1966a; NE Atlantic Shelf (Montagu, 1808) (Müller, 1776) Oldfi eld 1961 TScintillona brissae Brissus latecarinatus Jespersen et al. SE Asia Sublittoral Morton & Scott, 1989 (Leske, 1778) 2004 TMontacutella echinophila Jespersen et al. Brissus latecarinatus SE Asia Sublittoral Jespersen et al., 2004 2004 TBrachiomya stigmata Jespersen et al. Brissus latecarinatus SE Asia Sublittoral (Pilsbry, 1920) 2004 TTellimya vitrea Brissus gigas (Fell, 1947) Ponder 1968 S. Australia Shallow shelf (Hedley, 1907) TTellimya vitrea aupouria New Brissus gigas Ponder 1968 Shallow shelf (Ponder, 1968) Zealand TMontacuta Echinocardium Habe 1964: echinocardiophila cordatum; Lovenia Jespersen et al. Japan Shallow shelf (Habe, 1964) elongata (Gray, 1845) 2004 Montacuta divaricata Schizaster lacunosus Jespersen et al. Japan Shallow shelf Gould, 1861 (Linnaeus, 1758) 2004 TMontacuta semiradiata Echinocardium sp; Ponder 1968; Barel S. Australia Shallow shelf Tate, 1889 Spatangus sp. & Kramers 1977 TMontacuta semiradiata New Cyclaster sp. Dell 1963 340-620 m neozelanica (Dell, 1956) Zealand WNeaeromya compressa ? Brissaster latifrons Coan et al. 2000 NE Pacifi c 10-700 m (Dall, 1899) (Agassiz, 1898) TKelliola symmetros Aeropsis rostrata This paper N. Atlantic 3000 m (Jeffreys, 1876) (Wyville Thomson, 1877) Syssitomya pourtalesiana Pourtalesia jeffreysi & Bouchet & Warén N. Atlantic 800-3000 m sp. nov. P. miranda. 1979 TPtilomyax hadalis Pourtalesia heptneri Banda Mironov 1978 7340-7335 m sp. nov. Mironov, 1978 Trench Sternospatangus sibogae Mironov pers. Unidentifi ed Deep-sea (de Meijere, 1904) comm. Carnarechinus clypeatus Unidentifi ed Mironov 1993 S. Atlantic Deep-sea (Agassiz, 1879) Axinodon symmetros (Jeffreys, 1876) and is associated with Pourtalesia jeffreysi Wyville Thomson, 1877 and P. miranda Agassiz, 1869 (Bouchet & Warén 1979; Gage et al. 1985). The synonymy of Kellia symmetros and Axinodon ellipticus Verrill & Bush, 1898 was fi rst made by Ockelmann in Chavan (1969). Dall (1899) noting discrepancies in Jeffreys original description of K. symmetros placed it in a new genus Kelliola Dall, 1899; this was synonymised with Axinodon by Chavan (1969). In the original descriptions of “Kellia” symmetros (Jeffreys 1876) and Axinodon ellipticus (Verrill & Bush 1898) there is no mention of an association with echinoids. The fi rst mention