Taxonomy and phylogeny of mud owls (Annelida: Sternaspidae), including a new synonymy and new records from the Southern Ocean, North East Atlantic Ocean and Pacific Ocean: challenges in morphological delimitation

Greg W. Rouse,Magdalena N. Georgieva,Xuwen Wu,Adrian G. Glover,Regan Drennan,Helena Wiklund,Genki Kobayashi,Kenji Yoshino

doi:10.1007/s12526-019-00998-0

Abstract

Species delimitation in sternaspid polychaetes is currently based on the morphology of a limited suite of characters, namely characters of the ventro-caudal shield—a unique feature of the family. Sternaspid species description has increased rapidly in recent years; however, the validity of the shield as a diagnostic character has not been assessed through molecular means. This study performs the largest molecular taxonomy of Sternaspidae to date, using the nuclear gene 18S, and the mitochondrial genes 16S and cytochrome oxidase subunit I (COI) to assess phylogenetic relationships within the family, to reassess the placement of Sternaspidae within the wider polychaete tree and to investigate the effectiveness of the shield as a diagnostic morphological character. This study includes many new records and reports Sternaspis affinis Stimpson, 1864 from USA Pacific coastline and genetic connectivity between specimens identified as Sternaspis cf. annenkovae Salazar-Vallejo & Buzhinskaja, 2013 from off southeastern Australia and specimens identified as Sternaspis cf. williamsae Salazar-Vallejo & Buzhinskaja, 2013 from the northwestern Pacific. In addition, we investigate material identified as Sternaspis cf. scutata (Ranzani, 1817) in the English Channel and compare with S. scutata through both molecular and morphological means. We further perform a detailed morphological and molecular investigation of new sternaspid material collected from the Southern Ocean and Antarctic Peninsula and regard Sternaspis monroi Salazar-Vallejo, 2014 syn. n. as a junior synonym of Sternaspis sendalli Salazar-Vallejo, 2014, two species recently described from the region, raising questions concerning the validity of current morphological delimitation.

Highlights

Sternaspid polychaetes are widespread and often abundant in sedimented sea floors, reported globally from a variety of substrates, including gravelly muds (Hartman 1963), coarse sand, broken shells, soft mud (Treadwell 1914) and deep-sea clays and muds (Rouse and Pleijel 2001), at depths ranging from low intertidal to at least 6489 m
This study found evidence of multiple unidentified species amongst GenBank specimens recorded as S. scutata from non-type localities, though revealed intraspecific connectivity over a large geographic range in a case study of deepwater specimens from the northwestern Pacific Ocean identified as Sternaspis cf. williamsae Salazar-Vallejo & Buzhinskaja, 2013
The position of Fauveliopsidae in this study was unresolved—this is likely due to a lack of data, as the analysis was limited to three genes and only three fauveliopsid sequences were available for use, two 18S sequences and one 16S sequence (Online Resource 3), with one of the 18S sequences (Fauveliopsis sp.) shown to be long branched in relation to other sequences in the dataset

Summary

Introduction

Sternaspid polychaetes are widespread and often abundant in sedimented sea floors, reported globally from a variety of substrates, including gravelly muds (Hartman 1963), coarse sand, broken shells, soft mud (Treadwell 1914) and deep-sea clays and muds (Rouse and Pleijel 2001), at depths ranging from low intertidal to at least 6489 m Sternaspidae is comprised of 43 species in three genera, with the largest genus, Sternaspis Otto, 1821 (Annelida: Sternaspidae Carus, 1863), containing 33 species (Salazar-Vallejo 2017). Both morphological assessments (Rouse and Fauchald 1997; Rouse and Pleijel 2001) and molecular phylogenetics (Rousset et al 2007; Struck et al 2007; Struck et al 2008; Andrade et al 2015) consistently place Sternaspidae as a sister taxon to Fauveliopsidae; the affinities of this sister pair to other families remains unclear (Osborn and Rouse 2011). Assessments of within-Sternaspidae relationships are scant, primarily limited to morphological cladistics (Sendall 2006), with only a single molecular investigation conducted far (Kobayashi et al 2018)

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