Antonbruunia sociabilis sp. nov. (Annelida: Antonbruunidae) associated with the chemosynthetic deep-sea bivalve Thyasira scotiae Oliver & Drewery, 2014, and a re-examination of the systematic affinities of Antonbruunidae

Abstract

Antonbruunia sociabilis sp. nov., an abundant endosymbiont of Thyasira scotiae from a putative sulphidic ‘seep’ in the Hatton-Rockall Basin (1187–1200 m), North-East Atlantic Ocean, is described. The new species is compared with A. viridis and A. gerdesi from the West Indian Ocean and South-East Pacific Ocean respectively. The three species can be distinguished using a suite of morphological characters, and are associated with geographically separated chemosynthetic bivalve molluscs from different families (Thyasiridae, Lucinidae, Vesicomyidae) living in sediments at different depths. New morphological features are recognized for Antonbruunia and a re-assessment of its systematic affinities indicates a close relationship with the Pilargidae. Previous suggestions of an affiliation with the Nautiliniellidae, recently incorporated into the Calamyzinae (Chrysopetalidae), were not supported. The apparent morphological similarities between the two groups are indicative of convergence related to their shared relationships with chemosynthetic bivalves. The first molecular analyses of Antonbruunia (16S and 18S rDNA) clearly indicate that a close relationship to Pilargidae (represented by Ancistrosyllis sp. and Sigambra sp.) is more likely than an affinity to Calamyzinae (represented by Calamyzas amphictenicola, Natushima sp., and Vigtorniella sp.).

Behavioral traits and territoriality in the symbiotic scaleworm Ophthalmonoe pettiboneae

“…associated with a single host species), but showing a variety of spacing systems and intraspecific association patterns on/in their hosts 18 , 37 . Serpulids and antonbruunids show dense unstructured aggregations and probably lack territorial behavior 38 – 40 , while chrysopetalids and polynoids may occur as heterosexual pairs 41 , 42 . Most commonly, however, symbiotic polychaetes live solitary on their hosts 18 , 37 .…”

A Mitogenome-Based Phylogeny of Pilargidae (Phyllodocida, Polychaeta, Annelida) and Evaluation of the Position of Antonbruunia

“…When Pilarginae was erected, Paracabira, now Cabira, was thought to lack lateral antennae; however, they are just small [82]; this brings the antennae count from 0-3 to 2-3. Emergent neuropodial hooks are absent from all pilargids [7,13], but the presence (Ancistrosyllis, Cabira, Sigambra) or absence (Pilargis) of emergent notopodial hooks or spines remains. Sigambra and some Ancistrosyllis have termi-nal papillae on the proboscis [13] Pilargidae with body cylindrical or dorsoventrally flattened, integument smooth.…”

“…The authors generated mitochondrial 16S rRNA (16S) and nuclear 18S rRNA (18S) sequences to assess the phylogenetic placement of Antonbruunia. Although the molecular phylogenies of Mackie et al [7] included sequences of Antonbruunia sociabilis and representatives from fifteen other families of annelids, the position of Antonbruunia varied across their analyses, though the Bayesian analysis of the combined data suggested a sister group relationship to the included pilargids. The sampling of pilargids (Ancistrosyllis McIntosh, 1878, and Sigambra Müller, 1858 [7]) was insufficient to assess whether Antonbruunia falls within Pilargidae.…”

“…Such is the case for Antonbruunia Hartman and Boss, 1965, a genus of inquiline phyllodocid annelid worms that live inside chemosynthetic bivalves from the families Lucinidae Fleming, 1828, Thyasiridae Dall, 1900Dall, (1895, and Vesicomyidae Dall and Simpson, 1901 [7]. Antonbruunia are mostly found in the deep sea, and each species has been encountered only once [7][8][9]. The first species to be described, Antonbruunia viridis Hartman and Boss 1965, was found inhabiting the mantle cavity of Opalocina fosteri (Hartman and Boss 1965) (Bivalvia: Lucinidae) off the coast of Madagascar at a depth of 70 m. In each opened bivalve, there was almost always one smaller male and one larger female present.…”

“…Within three of the four bivalves where the species was found, there was only a single worm, while the fourth bivalve contained three. Mackie et al found a third species, Antonbruunia sociabilis Mackie, Oliver and Nygren, 2015, inside Thyasira scotiae Oliver and Drewery, 2014 (Bivalvia: Thyasiridae), off the coast of Scotland at a depth of 1200 m [7]. The name refers to the fact that multiple specimens were found within each dissected clam.…”