Nectoneanthes Imajima 1972

Genus Nectoneanthes Imajima, 1972

Nectoneanthes Imajima, 1972: 113; Fauchald, 1977: 89–90; Wu et al., 1985: 161; Khlebovich, 1996: 114.

Prostomium with entire anterior margin, one pair of antennae, one pair of palps, two pairs of eyes. Eversible proboscis with conical paragnaths on both maxillary and oral rings. Four pairs of tentacular cirri. Parapodia of first two chaetigers sub-biramous, all following parapodia biramous. Sub-biramous parapodia with thin notoacicula and thick neuroacicula. Notopodia consisting of dorsal cirrus, dorsal ligule, prechaetal lobe and ventral ligule in biramous parapodia; notopodial dorsal ligule expanded with prominent ovoid lobe developing above dorsal cirrus in middle and posterior parapodia even in atokes. Neuropodia consisting of inferior lobe, postchaetal lobe, ventral ligule and ventral cirrus throughout; all neuropodial lobes and ligule slen- der and conical. Notochaetae homogomph or sesquigomph spinigers. Neurochaetae in both upper and lower fascicles consisting of homogomph or sesquigomph spinigers and heterogomph spinigers. Falcigers absent except for neurochaetae in juveniles.

Nectoneanthes was synonymized with Neanthes Kinberg, 1865 by Wilson (1988), and later with Alitta Kinberg, 1865 by Bakken and Wilson (2005), based on Wilson’s (1988) incorrect judgement that Nectoneanthes oxypoda is synonymous with Neanthes succinea. However, Nectoneanthes is here resurrected based on the present results showing that this genus is clearly distinguishable from Alitta and Neanthes in the atokous morphology: the presence of an ovoid lobe above the dorsal cirrus in the middle and posterior parapodia even in atokes, and the absence of a falciger except in an early stage in juveniles are diagnostic characteristics separating Nectoneanthes from Alitta and Neanthes (see details below).

Cheilonereis Benham, 1916 is very similar to Nectoneanthes in terms of the presence of an ovoid lobe above the dorsal cirrus on the notopodial ligule in atokes, but is different from it in terms of the expanded peristomium, persistent presence of falcigers, and the absence of notoacicula in the first two chaetigers.

Paraleonnates Khlebovich and Wu, 1962 is similar to Nectoneanthes in terms of the presence of a small lobe above the dorsal cirrus in the posterior notopodia and the absence of falcigers in the atokes, but is different from it in terms of the presence of papillae on the oral ring of the proboscis and in the morphology of the parapodial lobes (see also Hong et al. 2012).

The following two species are included in Nectoneanthes: Nectoneanthes oxypoda (Marenzeller, 1879) and Nectoneanthes uchiwa sp. nov. All other nominal species previously referred to as Nectoneanthes have been judged as junior synonyms of N. oxypoda (see details below). It is deferred to further studies whether Nectoneanthes sp. that Al-Hakim and Glasby (2004) tentatively reported from the Natuna Islands in South China Sea is an undescribed species belonging to this genus or not.

1. Broad continuous band of many paragnaths (more than 200) present in oral ring of proboscis covering groups V and VII–VIII, except for group VI remaining in compact clusters separated from other paragnaths...................................................................... N. uchiwa sp. nov. Two or three transverse rows of paragnaths present in group VII–VIII, not continuous to group V...................... N. oxypoda (Marenzeller, 1879)