Nereis species groupings Salazar-Vallejo et al. (2021) attempted to divide Nereis into different groups based on the tooth features of the homogomph falcigers blade, the development and shape of parapodial ligules, and the pharyngeal paragnath patterns in areas VII–VIII. Although not stated, a similar arrangement appears to have been followed, as described by Wilson (1984) for Neanthes. However, only a single demonstrative Nereis species is mentioned, rendering the total number and the members of the Nereis groupings unknown. Given the differences in shape and number of teeth of the homogomph falcigers’ blades between middle and posterior parapodia, as well as the homogomph falciger blades’ dependence on age and size in some species (Fauvel 1914; Villalobos-Guerrero, pers. obs.), those blades’ features are troublesome for practical species designations into groups. Further, alternative, less variable characters for creating groupings of large Nereididae genera have been proposed elsewhere (Villalobos-Guerrero et al. 2021; Villalobos-Guerrero & Idris 2021). Groupings could be formed primarily through the enlargement of the dorsal cirrophore, followed by the simultaneous usage of another three less variable features, such as the presence of neuropodial postchaetal and superior lobes, the presence of homogomph spinigers in the subacicular neurochaetae, or the number of rows on the anterior band of areas VII– VIII. Other recently proposed diagnostic characters may also be useful for practical purposes in distinguishing species within convoluted genera, including the presence of notoacicula in the first two parapodia and oesophageal caeca, the merged paragnaths on area IV, and the ridge patterns of areas VI–V–VI (Villalobos-Guerrero et al. 2021; Villalobos-Guerrero & Idris 2021). Currently, Nereis comprises approximately 230 species, many of which are likely to belong to other genera (Wilson et al. 2023). The current diagnosis modified in the present study is, therefore, heterogeneous because it encompasses species with dissimilar morphology and markedly different to that of the type species Nereis pelagica Linnaeus, 1758. For instance, it includes members with extended and flattened posterior dorsal cirrophores, such as N. grubei (Kinberg, 1865), N. inflata de León-González & Solís-Weiss, 2001, N. lamellosa Ehlers, 1868, N. ligulata Hilbig, 1992, N. piscesae Blake & Hilbig, 1990, and N. vexillosa Grube, 1851; also, species with markedly elongated ligule(s), such as N. angelensis Fauchald, 1972, N. anoculopsis Fauchald, 1972, N. fossae Fauchald, 1972, and N. longilingulis Monro, 1937; or species with dorsal ligule markedly reduced in posterior chaetigers, as for N. caecoides Hartman, 1965, N. caymanensis Fauchald, 1977, and N. costaricaensis Dean, 2001. It is urgently necessary to revise the Nereis genus and, when possible, include molecular studies.

Published as part of Pradhan, Jyoshna, Villalobos-Guerrero, Tulio F. & Mohapatra, Anil, 2025, Description of two new species of nereidids (Annelida: Nereididae) from West Bengal, India, Bay of Bengal, pp. 335-348 in Zootaxa 5729 (2) on page 346, DOI: 10.11646/zootaxa.5729.2.6, http://zenodo.org/record/17936063