Nereis Linnaeus, 1758

Conde-Vela, Victor M. & Salazar-Vallejo, Sergio I., 2015, Redescriptions of Nereisoligohalina (Rioja, 1946) and N. garwoodi Gonzalez-Escalante & Salazar-Vallejo, 2003 and description of N. confusa sp. n. (Annelida, Nereididae), ZooKeys 518, pp. 15-49 : 17-18

Taxon classification Animalia Phyllodocida Nereididae

Genus Nereis Linnaeus, 1758

Type species.

Nereis pelagica Linnaeus, 1758, by subsequent designation ( Hartman 1948:63).

Remarks.

Linnaeus (1758:654) listed five species under Nereis : Nereis lacustris (now Stylaria lacustris , an oligochaete), Nereis caerulea (questionable after Hartman 1959:254), Nereis gigantea (after Hartman 1959:259, same as Hermodice carunculata (Pallas, 1766), rendering it a nomen oblitum because it would have priority over Pallas’ name), Nereis pelagica , and Nereis noctiluca . Further, it was Hartman (1948:63) who fixed the type species, and therefore this should be regarded as a subsequent designation ( ICZN 1999, Art. 69.1), in contrast to Bakken and Wilson (2005) who regarded it as an original designation.

Although the species described here have more attributes than those included in the current diagnosis of the genus ( Bakken and Wilson 2005), the generic diagnosis was not modified because it first requires a redescription of the type-species, and a phylogenetic analysis with subsequent delimitation of the genus. Among the traditionally used features for descriptions and delimitation of Nereis species are some that are highly variable, especially paragnath number. Bakken et al. (2009) made a useful revision of paragnath morphology and introduced new terminology to standardize descriptions. In addition to conical paragnaths, the species described here present other types of paragnaths that are not currently included in the diagnosis of the genus. Conical paragnaths are pointed to various degrees, being more acute in the maxillary ring, especially on area II. The pyramidal paragnaths in Nereis oligohalina and Nereis garwoodi have quadrilateral bases but they can also be polygonal, having more defined surfaces in the latter species. Further, Nereis confusa sp. n. apparently has smooth bars on area IV, but a closer inspection confirms that this is an artifact because the bars are formed by lateral and basal fusions of some small conical paragnaths (Fig. 6H); these modified structures were regarded as melted paragnaths ( Bakken et al. 2009). However, Glasby et al. (2011) suggested limiting use of the term for conical paragnaths mounted on a plate-like basement as occurs in Neanthes pachychaeta (Fauvel, 1918), and Villalobos-Guer rero and Carrera-Parra (2015) found paragnaths on a soft basement in Alitta acutifolia (Ehlers, 1901). Because neither a basement is present in Nereis confusa sp. n., we suggest the term ‘merged’ for paragnaths fused at the base but without formation of a plate.

In his revision of Pseudonereis Kinberg, 1865, Bakken (2007) introduced the term ‘P-bar’, which was later defined by Bakken et al. (2009) as "small bars having a protruding apex in one end of the bar"; and they can appear in areas II, III, IV and VII-VIII, often accompanied by conical paragnaths. The monophyly of Pseudonereis was supported by, among other characters, the presence of both P-bars and paragnaths in comb-like rows ( Bakken 2007). The Nereis species studied herein have two main rows, each one with other two sub-rows; the anterior-most sub-rows are often aligned horizontally, while the posterior-most ones form a jagged line. The anterior-most rows have P-bars alternating with conical or pyramidal paragnaths in a similar way as in Pseudonereis (Fig. 6 D–F), which has been also reported for Alitta ( Villalobos-Guerrero and Carrera-Parra 2015). Therefore, P-bars are not an exclusive feature of Pseudonereis as Bakken et al. (2009) concluded.

The neuropodial postchaetal lobe has been considered absent for Nereis species in recent phylogenetic analyses ( Bakken and Wilson 2005, Santos et al. 2005). Nevertheless some authors indicate its presence; Read (1980) for Nereis ovarius (Read), Santos and Lana (2003) for Nereis pseudomoniliformis (Santos and Lana), Chambers and Garwood (1992) for Nereis pelagica (and corroborated by us), and Darbyshire (2014) for Nereis eugeniae (Kinberg, 1865). Also, the three species herein described have postchaetal lobes shorter or subequal than neuroacicular ligules, and in epitoke specimens these lobes carry natatory lamellae; therefore, we considered postchaetal lobes as present in Nereis .

Reproductive nereidids or epitokes can have two or three different regions; parapodial cirri and the pygidium are transformed is especially relevant for chemorreception, parapodial lobes or ligules are expanded and chaetae replaced for swimming ( Herpin 1925, Boilly-Marer 1972). Charrier (1920) studied muscular tissue transformation associated with epitoky in the commensal species Nereis fucata (Savigny in Lamarck, 1818) (currently belonging to Neanthes Kinberg). He observed that parapodial cirri vary in some features as the length relative to corresponding ligules, the modifications of attachment and the displacement along the body; in fact, the attachment site of dorsal cirrus often show a distal displacement along notopodial ligules.