Reproductive morphology and redescriptions of some Neanthes Kinberg, 1865 (Annelida: Nereididae) species from the southeastern Asian seas, with comparative synoptic tables of accepted species

Abstract

Neanthes Kinberg, 1865 is a speciose nereidid genus with some species exhibiting epitoky during the timing of reproduction. The epitokal morphology of males and females has long been agreed to be diagnostic to distinguish species. In the present study, we provide redescriptions of the type material and reassess the current taxonomic status of four Neanthes species originally described based on the reproductive forms of specimens collected from Southeast Asia: Neanthes augeneri (Gravier & Dantan, 1934), N. gisserana (Horst, 1924), N. trifasciata (Grube, 1878) and N. trifasciata vandersandei (Horst, 1924). The non-metamorphosed and epitokous diagnostic features, including new characters found in this study, were used to redescribe and distinguish these species from other congeners. The four species are here recognised in Neanthes, whereby N. vandersandei is elevated to species level. Neanthes gisserana is considered as distinct from its previous senior synonym N. rubicunda (Ehlers, 1868). Morphology of both N. trifasciata and N. vandersandei, originally described based on mixed species, is restricted. Additionally, some remarks on the status of N. thysanota (Ehlers, 1908) are given. Distributional and reproductive data of the reviewed species are provided. An updated checklist of 80 valid species in Neanthes and synoptic tables of diagnostic features including the atokous and epitokous morphology are also presented.

A remarkable new deep-sea nereidid (Annelida: Nereididae) with gills

“…In contrast, those in Dendronereis Peters, 1854 are markedly modified dorsal cirrophores with bipinnate shapes, consisting of branches arising laterally from the primary axis. Enlarged dorsal cirrophores have also been reported as gills in Gymnonereis [ 95 ], Namalycastis [ 89 , 96 ], Nereis [ 97 ], and Tambalagamia Pillai, 1961 [ 98 ], and those highly vascularized should also be treated in the same manner in members of Alitta (see [ 49 ]: Figs 2F and 3E; [ 99 ]: Figs 3E–3G, 9F, 17K and 18G), Nectoneanthes ([ 100 ]: Figs 8D and 11D and 14D), Stenoninereis ([ 90 ]: Figs 2D and 5D), as well as some Neanthes with enlarged dorsal cirrophores (see [ 101 ]: table II, as shape of dorsal ligule), among others.…”

Redescriptions of Neanthes Kinberg, 1865 (Annelida: Errantia: Nereididae) species from worldwide regions

“…The definition of the polyphyletic genus Neanthes introduced earlier by Bakken & Wilson (2005) through morphological phylogenetic analysis of Nereidinae sensu Fitzhugh (1987) and modified by Glasby (2015) and Villalobos-Guerrero & Idris (2021) is followed in the present study. For further details on the current taxonomic situation of the genus, see Davenport et al (2020) and Villalobos-Guerrero & Idris (2021). The four species here morphologically delimited are still retained in Neanthes considering that genus definition.…”

“…Neanthes is currently an artificial genus with polyphyletic origin (see Bakken & Wilson 2005) that presents problematic differences with other similar genera, such as Hediste Malmgren, 1867, Nereis Linnaeus, 1758, Perinereis Kinberg, 1865and Simplisetia Hartmann-Schröder, 1981(Hartmann-Schröder 1996Glasby et al 2011;Villalobos-Guerrero & Idris 2021;Villalobos-Guerrero et al 2021). This has caused a continuous extension of the genus diagnosis to include species that cannot be assigned to other nereidid genera with conical paragnaths and spinigerous notochaetae only (e.g., Glasby et al 2011;Hsueh 2019aHsueh , 2019bIbrahim et al 2019), but whose overall morphology is distinctly different from the type species of the genus, Neanthes vaalii Kinberg, 1865.…”

“…This has caused a continuous extension of the genus diagnosis to include species that cannot be assigned to other nereidid genera with conical paragnaths and spinigerous notochaetae only (e.g., Glasby et al 2011;Hsueh 2019aHsueh , 2019bIbrahim et al 2019), but whose overall morphology is distinctly different from the type species of the genus, Neanthes vaalii Kinberg, 1865. Several studies have attempted to reduce this heterogeneity by transferring distinct species to other genera (Bakken 2007;Sato 2013;Villalobos-Guerrero & Carrera-Parra 2015;Villalobos-Guerrero 2019;Villalobos-Guerrero & Idris 2020;Villalobos-Guerrero et al 2021). Nonetheless, Neanthes remains poorly understood and, thus, is in urgent need of accurate morphological delimitation of the species that aids to redefine the genus through a comprehensive revisionary work (Pamungkas & Glasby 2015;Bakken et al 2018;Ibrahim et al 2019;Sato 2020;Davenport et al 2020;Villalobos-Guerrero & Idris 2021;Villalobos-Guerrero et al 2021).…”

“…Several studies have attempted to reduce this heterogeneity by transferring distinct species to other genera (Bakken 2007;Sato 2013;Villalobos-Guerrero & Carrera-Parra 2015;Villalobos-Guerrero 2019;Villalobos-Guerrero & Idris 2020;Villalobos-Guerrero et al 2021). Nonetheless, Neanthes remains poorly understood and, thus, is in urgent need of accurate morphological delimitation of the species that aids to redefine the genus through a comprehensive revisionary work (Pamungkas & Glasby 2015;Bakken et al 2018;Ibrahim et al 2019;Sato 2020;Davenport et al 2020;Villalobos-Guerrero & Idris 2021;Villalobos-Guerrero et al 2021).…”