Nereis shinkai (Shimabukuro et al., 2017) comb. nov.

(Figs 14, 15)

Neanthes shinkai Shimabukuro, Santos, Alfaro-Lucas, Fujiwara % Sumida, 2017.

Material examined: Paratype 3 (ColBIO-DS 00004), incomplete, 28 cht, 30.7 mm long, 6.6 mm wide. Three specimens coll. 25 May 2015, continental margin off São Paulo state, Santos Basin, Brazil, 28°01ʹ42.24″S, 43°31ʹ46.8″W, 3358 m depth; specimen complete, but fractioned, 55 cht, 44.6 mm long, 3.6 mm wide (MZUSP5355); specimen incomplete, 10 cht, 9 mm long, 2.5 mm wide (ColBIO-DS 00199); juvenile specimen incomplete, 16 cht, 6.2 mm long, 0.8 mm wide (MZUSP5356).

New report: Three specimens (two adults and one juvenile) found at the ‘SP3300’ site (Table 1; Fig. 1) belong to the species Nereis shinkai, confirmed by both morphological and molecular data (Fig. 2). Still, there are some morphological variations between specimens from the ‘Shinkai’ site (original description) and the ‘SP3300’ site (present study) that are presented in the following Variation section. The geographical proximity between the two collection sites supports the specimens belonging to the same species, and both sites are influenced by the same water mass, the Antarctic Bottom Water, but this new report is important by the extension of the depth range of the species, with the ‘Shinkai’ site at 4204 m and the ‘SP3300’ site at 3358 m.

Variation: Specimens from this study present posterodorsal tentacular cirri reaching chaetiger 5 (Fig. 14A, B), whereas in the original description, specimens of Nereis shinkai presented tentacular cirri reaching chaetiger 2. The other prostomial and peristomial features are identical, including the position and length of palps and antennae (Fig. 14A, B, D). The jaws are identical, and the paragnaths present a similar distribution and number, as shown in Table 4, with the exception of areas VII and VIII, which present 13 paragnaths in an irregular row in the original description and ~70 paragnaths concentrated in the groove in specimens from the ‘SP3300’ site. Part of this difference can be related to the loss of the fragile paragnaths in specimens from the original description. Uniramous parapodia of the species from the ‘SP3300’ site presented ligules slightly rounded (Fig. 15A), a feature not reported in the original description, but morphological features of biramous parapodia are similar for all specimens (Fig. 15B–E). Specimens from the ‘SP3300’ site present heterogomph falcigers with both short (Fig. 15K) and long blades (Fig. 15F) and, although not specified in the original description, both types of blades were found on heterogomph falcigers of the paratype 3 of Nereis shinkai (ColBio-DS 00004). Heterogomph falcigers from Nereis shinkai collected at the ‘SP3300’ site are also of two types, with long (Fig. 15H) and short blades (Fig. 15I), whereas on specimens from the ‘Shinkai’ site there are only long-bladed heterogomph falcigers. But the most outstanding variation between specimens from these different locations is the presence of homogomph falcigers (Fig. 15H, J) on specimens from the ‘SP3300’ site, whereas they are absent on specimens from the original description. Lastly, the pygidium of specimens from the ‘SP3300’ site presents a pair of cirri reaching the last 22 chaetigers (Fig. 14C), whereas pygidial cirri of specimens from the original description reach the last 10–15 chaetigers.

The observed juvenile from the ‘SP3300’ site presents palpophores more slender than in adults and with the same length of palpostyles; palps and antennae directed frontally and notopodial lobes two-fifths longer than notopodial ligules in all parapodia.

Remarks: The species previously described as Neanthes shinkai Shimabukuro et al., 2017 is nested within the Nereis clade according to the phylogenetic reconstruction using both COI and 16S genes (Fig. 2), more specifically identical to specimens from the ‘SP3300’ site from this study and within the eyeless Nereis clade from organic falls. In the original description, the species was assigned morphologically to Neanthes owing to the lack of homogomph falcigers, an important feature differing in Nereis and Neanthes, but specimens of Nereis shinkai from the ‘SP3300’ site present homogomph falcigers in the posterior notopodia. This morphological feature, together with the molecular and phylogenetic analyses, supports the reassignment of the species as Nereis shinkai but raises an issue of variation in the presence of homogomph falcigers within the same species, which will be discussed in the Discussion section.