Abstract
The present study redescribes four species of Neanthes Kinberg, 1865 (Nereididae de Blainville, 1818) based on their type specimens collected from different worldwide localities: Neanthes chilkaensis (Southern, 1921) from India, N. galetae (Fauchald, 1977) from Panama, N. helenae (Kinberg, 1865) from St Helena Island, and N. mossambica (Day, 1957) from Mozambique. The morphology of the types was re-examined for the first time after the species were originally described, and incorporated the recent improvements in the standards and terminology for describing nereidid features. The arrangement of paragnaths on area VI stood out among the diagnostic features used to distinguish these four species. Neanthes chilkaensis and N. helenae are the unique nereidids bearing p-bar paragnaths on the area VI. Both species are also distinctive as the former species only exhibited p-bar paragnaths on the area VII–VIII and the latter ventrolateral projections on the apodous segment. Further examination revealed that N. nanciae (Day, 1949) from St Helena is a junior synonym of N. helenae. Moreover, N. galetae and N. mossambica are distinguishable from other species also by the development of dorsal cirri, neuropodial postchaetal lobe and ventral ligule, the presence/absence of merged paragnaths on area IV, paired oesophageal caeca, among other features. This study has further contributed to the morphological delimitation of the species in Neanthes as a first step towards revising the genus.
Highlights
Nereididae de Blainville, 1818 is a common annelid family with a high number of valid taxa comprising 47 genera and 693 species
Neanthes is currently an artificial genus with polyphyletic origin that presents problematic differences with other similar genera, such as Hediste Malmgren, 1867, Nereis Linnaeus, 1758, Perinereis Kinberg, 1865 and Simplisetia Hartmann-Schröder, 1981 (HartmannSchröder 1996; Glasby 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 2019a, 2019b; Ibrahim et al 2019), but whose overall morphology is distinctly different from the type species of the genus, Neanthes vaalii Kinberg, 1865
The total length (TL), length from the distal end of prostomium to chaetiger 15 (L15), and body width at chaetiger 15 excluding parapodia (W15) were measured; and the total number of chaetigers was counted for complete specimens
Summary
Nereididae de Blainville, 1818 is a common annelid family with a high number of valid taxa comprising 47 genera and 693 species (de León-González et al 2020). 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, 1865 and Simplisetia Hartmann-Schröder, 1981 (HartmannSchröder 1996; Glasby et al 2011; Villalobos-Guerrero & Idris 2021; Villalobos-Guerrero et al 2021). Neanthes remains poorly understood and, 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)
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