Nereis, Linnaeus, 1758

Hsueh, Pan-Wen, 2020, New species of Nereis (Annelida, Polychaeta, Nereididae) from Taiwanese waters, Zootaxa 4802 (1), pp. 1-31 : 25-27

Nereis sp. A

Figs 18A – D, 19A–G

Material examined. One specimen ( NMNS 8174-036 ), Hooshia village (24°27.29´N 118°18.25´E), Kinmen County, Fujian, intertidal soft bottom, 20 February 2001 .

Brief description. Incomplete, remaining body length 53.0 mm with 42 chaetigers, maximum width 3.5 mm at apodous segment; brown in alcohol (Fig. 18A). Prostomium wider than long, lateral antennae antero-lateral; palpophores globose, palpostyles conical, four pairs of tentacular cirri, surface smooth, longest one reaching chaetiger 3 (Fig. 18A). Two pairs of eyes, in trapezoidal arrangement, subequal in size. Apodous anterior segment about 1.4 times as long as chaetiger 1. Pharynx with dark brown jaws, each with 10–11 teeth; I=3, in a longitudinal row; II =24 (left), 20 (right), in 3 oblique rows; III =42, in 4 transverse rows; IV =36 (left), 33 (right), in 3–4 irregular rows; V =0; VI =3 (left), 3 (right), in a triangle arrangement; VII / VIII =70, in 3–4 rows (Fig. 18B).

Notopodial dorsal ligules short, wide triangular on anterior chaetigers, dorsally expanded on mid-body chaetigers (Fig. 18C, D). Dorsal cirri basally attached to dorsal ligules, acute, about 3.0 times as long as dorsal ligules. Notopodial prechaetal lobes absent. Notopodial ventral ligules conical, rounded on anterior chaetigers, triangular, acute along mid-body chaetigers (Fig. 18C, D). Neuropodial postchaetal lobes absent. Neuropodial ventral ligules triangular on anterior and mid-body chaetigers, point-tipped; ventral cirri mid-ventrally attached to ventral edge of parapodia, acute, about as long as ventral ligules (Fig. 18C, D).

Notochaetae present from chaetiger 3 to posterior segments, homogomph spinigers present on anterior chaetigers (Fig. 19A), homogomph falciger present from chaetiger 22 to posterior segments, blade bent, blunt-tipped, base of blade margin with trace or conspicuous serrations (Fig. 19B, C). Neurochaetae upper fascicle: homogomph spinigers present (Fig. 19D), heterogomph falcigers with serrated medium-sized blade on anterior chaetigers and serrated shorter blade on posterior chaetigers (Fig. 19E). Neurochaetae ventral fascicle: heterogomph spiniger present (Fig. 19F), heterogomph falcigers with serrated medium-sized blade on anterior chaetigers and serrated shorter blade on posterior chaetigers (Fig. 19G).

Distribution. Only known from the Kinmen Island, Fujian.

FIG. 18. Nereis sp. A (NMNS 8174-036): A, anterior body; B, pharyngeal area; C, chaetiger 11, right parapodium, posterior view; D, chaetiger 36, right parapodium, anterior view. (Abbreviations: DC, dorsal cirrus; NeVL, neuropodial ventral ligule; NoDL, notopodial dorsal ligule; NoVL, notopodial ventral ligule; VC, ventral cirrus). Scale: A–B, 1.0 mm; C, 0.5 mm; D, 0.25 mm.

Remarks. Of the species reported from East Asia and the present study which Areas VII & VIII with three or more rows or a transverse band of paragnaths, only N. sp. A and N. sp. B do not have an isolate row of paragnaths on Areas VII & VIII (see the Key provided in the present study). The two species have similar paragnaths pattern, in which Areas I to V & VII/VIII of N. sp. A were 2, 21–21, 37, 11–30, 0 & 74, whereas those of N. sp. B were 3, 20–24, 42, 33–36, 0 & 70, respectively ( Table 2). However, difference in morphological features can be noticed. All paragnaths on the pharynx of N. sp. A are relatively large, compared to the relatively smaller ones in N. sp. B (Figs 18B, 20B). Nereis sp. A has fewer paragnaths on Area VI than N. sp. B (3 versus 5–7) (Figs 18B, 20B; Table 2). Moreover, N. sp. A has a different morphology of parapodia on anterior chaetigers and type of neuropodial heterogomph falcigers than that of N. sp. B (wide triangular dorsal ligules versus narrow triangular dorsal ligules and short and medium-sized blade neuropodial heterogomph falcigers versus medium and long-bladed neuropodial heterogomph falcigers, respectively) (Figs 18C, D, 19E, G, 20C, 21E, G, Table 2). Lastly, N. sp. A is an intertidal soft bottom dweller, whereas N. sp. B lives on soft bottom habitat in bathyal depth.

FIG. 19. Nereis sp. A (NMNS 8174-036): A, chaetiger 9, notochaetal homogomph spiniger; B, chaetiger 31, notochaetal homogomph falciger; C, chaetiger 33, notochaetal homogomph falciger; D, chaetiger 9, neurochaetal dorsal fascicle, homogomph spiniger; E, chaetiger 36, neurochaetal upper fascicle, short-bladed heterogomph falciger; F, chaetiger 9, neurochaetal ventral fascicle, heterogomph spiniger; G, same, neurochaetal ventral fascicle, medium-sized blade heterogomph falciger. Scale: A, D, F, 0.025 mm; B, C, E, G, 0.01 mm.