Two apparently unrelated groups of symbiotic annelids, Nautiliniellidae and Calamyzidae (Phyllodocida, Annelida), are a clade of derived chrysopetalid polychaetes

Abstract

Nautiliniellidae Miura and Laubier, 1989 is a small family of marine polychaetes with 20 currently described species in 11 genera, most of which are known to live symbiotically in the mantle cavity of bivalves, mainly from cold seeps and hydrothermal vents, while Calamyzidae (Hartmann‐Schröder, 1971) including only one described species, Calamyzas amphictenicola Arwidsson 1932 lives as an ectoparasite on ampharetid polychaetes in Swedish waters. Nautiliniellidae and Calamyzidae have both been considered to belong to Phyllodocida, but the few phylogenetic studies including these taxa have found their positions unstable. The internal relationships within Nautiliniellidae are also poorly understood. Using molecular information from both nuclear and mitochondrial genes and morphological data we assessed the systematic placement of Nautiliniellidae (seven species; collected from Pacific hydrothermal vents and cold seeps and one from Atlantic waters) and Calamyzas amphictenicola. Our results show that C. amphictenicola and Nautiliniellidae formed a well‐supported clade that is nested within Chrysopetalidae, a free‐living group of polychaetes. The chrysopetalid genus Vigtorniella Kiseleva 1992; a bacterial mat grazer found at methane seeps, anoxic basins and whalefalls, formed a paraphyletic grade with respect to the Nautiliniellidae–Calamyzas clade. The internal relationships within the Nautiliniellidae–Calamyzas clade as well as the relationships with their hosts are also examined. As a result we synonymize Calamyzidae and Nautiliniellidae with Chrysopetalidae, with the last as the oldest available family‐group name. Within Chrysopetalidae we refer to the subfamilies Chrysopetalinae Ehlers 1864; Dysponetinae Aguado, Nygren & Rouse, herein; and Calamyzinae Hartmann‐Schröder, 1971. Calamyzinae contains C. amphictenicola, all taxa formerly in Nautiliniellidae, and the chrysopetalid genus Vigtorniella.

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

“…The two antero-ventral prostomial appendages are here considered to be palps, while the two larger antero-dorsolateral organs are the lateral antennae. This is consistent with their positions on the prostomium in literature associated with Antonbruunidae (Fauchald 1977;Pleijel & Dahlgren 1998;Pleijel 2001c;Aguado et al 2013) and putative related families, Pilargidae (Pettibone 1966;Fitzhugh & Wolf 1990;Fauchald & Rouse 1997;Glasby 1993Glasby , 2000Pleijel 2001b) and Nautiliniellidae (Pleijel 2001a;Fauchald & Rouse 1997;Aguado & Rouse 2011;Aguado et al 2013). However, as Glasby (1993) pointed out, the true nature of the anteroventral appendages in Antonbruunia "must remain in doubt until better material is available to conduct histological study.…”

“…This has been followed by most subsequent workers (e.g. Pleijel 2001c; Aguado et al 2013). The diagnosis is emended following observations herein (see below) concerning the nuchal organs, notoacicula and parapodia, and segmental gut caecae.…”

“…Uncertainties surrounding Antonbruunia persist to the present day (e.g. Martin & Britayev 1998;Aguado & Rouse 2011), although the Nautiliniellidae are now regarded as part of the subfamily Calamyzinae within the Chrysopetalidae (Aguado et al 2013). The discovery of A. sociabilis enables us to re-assess the status of the Antonbruunidae from a morphological and molecular perspective.…”

“…6) and Polynoidae. Bivalve-dwelling calamyzins have neurochaetae that are superficially simple; however, there is some evidence that they may be derived from the fusion of shafts and blades of compound chaetae (Aguado & Rouse 2011;Aguado et al 2013). They are often unidentate, sometimes bidentate (e.g.…”

“…The Chilean species was less prevalent with only four of 35 C. gallardoi animals hosting a single individual, although three occurred in another. Calyptogena gallardoi was unusual in additionally hosting the 'nautiliniellid' (now part of Calamyzinae in Chrysopetalidae, see Aguado et al 2013) Shinkai robusta Quiroga & Sellanes, 2009 (single individuals in two of 35 bivalves), but there was no cooccurrence with A. gerdesi. Antonbruunia sociabilis is remarkable in having up to nine individuals inhabiting T. scotiae (maximum recorded size 19.8x19.6x12.56 mm).…”