Abyssal Solenogastres (Mollusca, Aplacophora) from the Northwest Pacific: Scratching the Surface of Deep-Sea Diversity Using Integrative Taxonomy

Abstract

Solenogastres (Aplacophora) is a small clade of marine, shell-less worm-molluscs with close to 300 valid species. Their distribution ranges across all oceans, and whereas the vast majority of species has been collected and described from the continental shelf and slope, only few species are known from depths below 4,000 m. Following traditional taxonomy, identification of specimens to species level is complex and time-consuming and requires detailed investigations of morphology and anatomy-often resulting in the exclusion of the clade in biodiversity or biogeographic studies. During the KuramBio expedition (Kuril-Kamchatka Biodiversity Studies) to the abyssal plain of the Northwest Pacific and the Kuril-Kamchatka Trench, 33 solenogaster specimens were sampled from 4,830 m to 5,397 m. Within this study we present an efficient workflow to address solenogaster diversity, even when confronted with a high degree of singletons and minute body sizes, hampering the use of single individuals for multiple morphological and molecular approaches. We combine analyses of external characters and scleritome with molecular barcoding based on a self-designed solenogaster specific set of mitochondrial primers. Overall we were able to delineate at least 19 solenogaster lineages and identify 15 species to family level and beyond. Based on our approach we identified three key lineages from the two regionally most species-rich families (Acanthomeniidae and Pruvotinidae) for deeper taxonomic investigations and describe the novel abyssal species Amboherpia abyssokurilensis sp. nov. (Cavibelonia, Acanthomeniidae) using microanatomical 3D-reconstructions. Our study more than doubles the previous records of solenogaster species from the Northwest Pacific and its marginal seas. Almost all lineages are reported for the first time from the region of the (Northwest) Pacific, vastly expanding distribution ranges of the respective clades. Moreover it doubles the number of Solenogastres collected from abyssal depths on a global scale and underlines the lack of exploratory α-diversity work in the abyssal zone for reliable species estimates in marine biodiversity.

Correct Species Identification and Its Implications for Conservation Using Haploniscidae (Crustacea, Isopoda) in Icelandic Waters as a Proxy

“…Originating in the 1970s, interactive keys using Descriptive Language for Taxonomy (DELTA) methodologies as an instrument for identifying species are not new (Dallwitz, 1974), but their use in deep-sea taxonomy has thus far been rudimentary (Saucède et al, 2021). Overall, there is a paucity of any type (paper or digital) of identification key and guide in general 3 and for deep-sea taxa in particular (Miljutin et al, 2010;Gollner et al, 2014;Bergmeier et al, 2017); instead, identifications are mostly based on descriptive works that are distributed throughout the literature (cf. Glover et al, 2021).…”

Biogeographic Atlas of the Deep NW Pacific Fauna

“…Prior to this recent expedition series to the spanning a depth range from 3,000 to more than 9,500 m (see Bergmeier et al 2017Bergmeier et al , 2020Ostermair et al 2018).…”

Four new Solenogastres (Mollusca, Aplacophora) from the South China Sea and paraphyly of Proneomeniidae Simroth, 1893

“…Therefore, for a first classification into morphospecies, the general external appearance is important, and several authors have highlighted the usefulness of this and the sclerites to discern between lineages (Scheltema et al . 2012; Kocot and Todt 2014; Bergmeier et al . 2017; Cobo and Kocot 2021).…”

“…The combination of the study of the scleritome and DNA barcodes has been shown to allow a tentative identification of specimens, albeit at the family level in some cases, without the need for time-consuming or expensive techniques, improving the ability to estimate the number of lineages in a collection (e.g. Bergmeier et al . 2017, 2019).…”