Nereis taitungensis, Hsueh, 2020

Hsueh, Pan-Wen, 2020, New species of Nereis (Annelida, Polychaeta, Nereididae) from Taiwanese waters, Zootaxa 4802 (1), pp. 1-31 : 17-19

Nereis taitungensis n. sp.

Figs 11A–G, 12A–L

Material examined. Holotype ( NMNS 8174-006 ), and six paratypes ( NMNS 8174-007 – 12 ), Jihuei (23°06.88´N 121°24.17´E), Taitung County, Taiwan, intertidal vegetated hard bottom, 7 October 2010; 1 specimen ( NMNS 8174-0013 ), Jihuei (23°06.88´N 121°24.17´E), Taitung County, Taiwan, intertidal vegetated hard bottom, 18 August 2012; 1 specimen ( NMNS 8174-014 ), Jihuei (23°06.88´N 121°24.17´E), Taitung County, Taiwan, intertidal vegetated hard bottom, 28 April 2017.

Description. Holotype (NMNS 8174-006), complete, ovigerous female, body length 28.0 mm with 50 chaetigers (17.0–24.0 mm with 50–59 chaetigers, n=6, based on complete specimens), maximum width 1.5 mm (1.0– 2.0, n=7) at chaetiger 10 (5–10, n=7), excluding parapodia; beige in alcohol (Fig. 11A). Prostomium wider than long, lateral antennae antero-lateral; palpophores globose, palpostyles conical, four pairs of tentacular cirri, surface smooth, longest one reaching anterior edge of chaetiger 1 (2 – 4, n=7) (Fig. 11B). Two pairs of eyes, in trapezoidal arrangement, anterior eyes larger than posterior ones. Apodous anterior segment about 1.7 times (1.3–1.5, n=8) as long as chaetiger 1. Pharynx with dark brown jaws, each with 6–7 (4–6, n=8) teeth; I=0 (0–1, n=8, same sample size for II to VIII); II=4 (3–10) (left), 6 (2–9) (right), in an oblique cluster or in 1–2 oblique rows; III=9 (3–11), in a cluster; IV=16 (11–25) (left), 15 (10–27) (right), in an oblique cluster; V=0 (0); VI=5 (9–17) (left), 6 (8–16) (right), in 2–3 transverse rows; VII/VIII=10 (12–25), in 1 row (Fig. 11C, D).

Notopodial dorsal ligules conical with rounded tip on anterior chaetigers, narrow triangular acute on posterior chaetigers (Fig. 11E–G). Notopodial prechaetal lobes absent. Dorsal cirri basally attached to dorsal ligules throughout, about 2.0 times as long as dorsal ligules on anterior chaetigers, about 4.5 – 5.0 times as long as dorsal ligules on posterior chaetigers (Fig. 11E–G). Notopodial ventral ligules conical with rounded tip on anterior chaetigers, narrow triangular with pointed tips on posterior chaetigers (Fig. 11E, F). Neuropodial ventral ligules conical on anterior, narrow triangular with acute tips on posterior chaetigers (Fig. 11E, F). Neuropodial postchaetal lobes absent. Ventral cirri basally attached to ventral edge of parapodia throughout, about as long as ventral ligule (Fig. 11E, F).

Notochaetae present from chaetiger 3 to posterior end, homogomph spinigers present on anterior chaetigers (Fig. 12A), homogomph falcigers present from chaetiger 18 (17–18, n=8) to posterior end, blade robust, slightly bent with 3 teeth (2–3, n=9, mostly 3 teeth), subdistal tooth largest (Fig. 12B–F). Neurochaetae upper fascicle: homogomph spinigers present (Fig. 12G), heterogomph falcigers with serrated short-blade (Fig. 12H, I). Neurochaetae ventral fascicle: heterogomph spiniger present (Fig. 12J), heterogomph falcigers with serrated short-blade (Fig. 12K, L). Pygidium round, one pair of filamentous anal cirri attached ventrally, as long as last 6 chaetigers (Fig. 11A).

Etymology. The name is derived from the name of a county on east coast of Taiwan where the worm was collected.

Type locality. Jihuei , Taitung County, Taiwan .

FIG. 11. Nereis taitungensis n. sp.; A, B, G, holotype ( NMNS 8174-006 ) ; C–E, paratypes ( NMNS 8174-010 ) ; F, paratypes ( NMNS 8174-012 ) : A, whole animal; B, anterior body; C, pharyngeal areas, dorsal view (arrows point to I, II, VI paragnaths); D, same, ventral view (arrows point to III, IV, VII / VIII paragnaths); E, chaetiger 10, right parapodium, anterior view; F, chaetiger 10, left parapodium, anterior view; G, chaetigers of posterior body segments. (Abbreviations: DC, dorsal cirrus; NeVL, neuropodial ventral ligule; NoDL, notopodial dorsal ligule; NoVL, notopodial ventral ligule; VC, ventral cirrus). Scale: A, 5.0 mm; B, 1.0 mm; C–F, 0.5 mm; G, 0.1 mm.

Distribution. Only known from Taitung County, Taiwan.

Remarks. As aforementioned, fourteen Nereis species reported from East Asia have Areas VII & VIII with 1or 2 transverse rows of paragnaths. Of these species, morphology of N. denhamensis Augener, 1913 , N. heteromorpha Treadwell, 1931 , and N. jacksoni Kinberg, 1866 is somewhat similar to N. taitungensis n. sp. by sharing a similar form of notopodial homogomph falcigers ( Imajima 1972: 121, fig. 38h, i, 1996: 148, fig. 118h, i; Sun et al. 1978: 157, fig. 23g; Wu et al. 1981:88, 90, figs 50F, 51J; Fig. 12B-F). However, N. taitungensis n. sp. can be distinguished from N. denhamensis by having short-bladed heterogomph falcigers on ventral fascicle of neuropodia from chaetiger 3 to posterior chaetigers, whereas that of N. denhamensis has medium-sized blade of neuropodial heterogomph falcigers on anterior chaetigers ( Augener 1913: 158, text-fig 16b; Imajima 1972: 121, fig. 38j, l; Hutching & Turvey 1982: 126, fig. 11j, k; Fig. 12H, I, K, L). Nereis taitungensis n. sp. differs from N. heteromorpha by having: 1) more paragnaths on Area VI (mostly more than 10 in 2 transverse rows versus 5 – 6 in 1 transverse row); 2) greater length ratio between dorsal cirri and dorsal ligules on posterior chaetigers (about 4.5- 5.0 versus about 3.0); and 3) shortbladed neuropodial heterogomph falcigers (versus short and medium-sized blade) ( Horst 1924: 153, pl. XXXI, fig. 2; Sun et al. 1978: 157, fig. 23e, f, h, l; Figs 11E, F, 12H, I, K, L, Table 2). Nereis taitungensis n. sp. can be distinguished from N. jacksoni by having: 1) more paragnaths on Areas VI (mostly 10 or more versus 2–4) and less paragnaths on Areas VII/VIII (10–25 versus 40–45); 2) greater length ratio between dorsal cirri and dorsal ligules on posterior chaetigers (about 4.5- 5.0 times versus about 3.0 times); and 3) short-bladed neuropodial heterogomph falcigers (versus medium-sized blade) ( Wu et al. 1981: 90, fig. 51F, I; Hutching & Turvey 1982: 129, fig. 13b; Fig. 12H, I, K, L, Table 2)

FIG. 12. Nereis taitungensis n. sp.; A, B, G–K, holotype (NMNS 8174-006); C, paratypes (NMNS 8174-009); D, paratypes (NMNS 8174-007); E, paratypes (NMNS 8174-008); F, L, paratypes (NMNS 8174-010): A, chaetiger 10, notochaetal homogomph spiniger; B, chaetiger 43, notochaetal, homogomph falciger; C, chaetiger 23, notochaetal, homogomph falciger; D, same, notochaetal homogomph falciger; E, chaetiger 30, notochaetal homogomph falciger; F, chaetiger 44, notochaetal homogomph falciger; G, chaetiger 10, neurochaetal upper fascicle, homogomph spiniger; H, same, neurochaetal upper fascicle, short-bladed heterogomph falciger; I, chaetiger 43, neurochaetal ventral fascicle, short-bladed heterogomph falciger; J, chaetiger 10, neurochaetal ventral fascicle, heterogomph spiniger; K, chaetiger 43, neurochaetal ventral fascicle, short-bladed heterogomph falciger; L, chaetiger 44, neurochaetal ventral fascicle, short-bladed heterogomph falciger. Scale: A–G, J, 0.025 mm; H, I, K, L, 0.01 mm.