Nereis taiwanensis, Hsueh, 2020

Hsueh, Pan-Wen, 2020, New species of Nereis (Annelida, Polychaeta, Nereididae) from Taiwanese waters, Zootaxa 4802 (1), pp. 1-31 : 20-23

Nereis taiwanensis n. sp.

Figs 13A–I, 14A–G, 15A–H

Material examined. Holotype ( NMNS 8174-015 ), atokous stage: Wonlitong (21°59.77´N 120°42.27´E), Pingtung County, Taiwan, intertidal vegetated hard bottom, 19 November 2010 . Paratypes: 2 specimens ( NMNS 8174- 016 – 17 ), collection locality, habitat and date information same as holotype ; 1 specimen ( NMNS 8174-018 ), Jihuei (23°06.86´N 121°24.18´E), Taitung County, Taiwan, vegetated intertidal hard bottom, 5 December 2009 . Epitokous stage: 4 specimens ( NMNS 8174-019 – 22 ), Jihuei (23°06.86´N 121°24.18´E), Taitung County, Taiwan, intertidal vegetated hard bottom, 7 October 2010 .

Description. Holotype (NMNS 8174-015), atokous stage, complete, body length 7.5 mm with 42 chaetigers (7.0–11.0 mm with 39–42 chaetigers, n=3, based on complete specimens), maximum width 0.5 mm (0.4–0.5 mm, n=3) at chaetiger 5 (5–6 mm, n=3), excluding parapodia; beige in alcohol (Fig. 13A). Prostomium wider than long, lateral antennae antero-lateral, palpophores globose, palpostyles conical, four pairs of tentacular cirri, longest posterior one reaching chaetiger 3 (2–3, n=3) (Fig. 13B). Two pairs of eyes, in trapezoidal arrangement, subequal in size. Apodous anterior segment about 1.2 (1.0–1.3, n=3) times as long as chaetiger 1. Pharynx with light brown jaws, each with 9 or 10 (6–8, n=2) teeth; Areas I–III=0 (0, n=3; sample size of Areas II to VIII same as Area I) (Fig. 13C); IV=5 (4–5) (left), 7 (4) (right), in 1 oblique row (Fig. 13D); V=0; VI=0 (0–2) (left), 0 (0–2) (right), side by side when with 2 (Fig. 13E); VII/VIII=9 (7–9), in 1 row (Fig. 13F).

FIG. 13. Nereis taiwanensis n. sp.; A, B, holotype ( NMNS 8174-015 ) ; C, G, H, paratype ( NMNS 8174-017 ) ; D, I, paratype ( NMNS 8174-016 ) : A, whole animal; B, anterior body; C, close-up of anterior body; D, pharyngeal areas (arrow points to IV paragnaths); E, same (arrows point to VI paragnaths); F, same (arrows point to VII/VIII paragnaths); G, chaetiger 10, right parapodium, anterior view; H, close-up of chaetiger 10, right parapodium, anterior view; I, chaetiger 11, left parapodium, anterior view (Abbreviations: DC, dorsal cirrus; NeVL, neuropodial ventral ligule; NoDL, notopodial dorsal ligule; NoVL, notopodial ventral ligule; VC, ventral cirrus). Scale: A, 1.0 mm; B, 0.25 mm; C, 0.1 mm; D–F, H, 0.05 mm; G, I, 0.1 mm.

Notopodial dorsal ligules small, bluntly rounded on anterior chaetigers (Fig. 13G–I), becoming conical on posterior chaetigers. Dorsal cirri basally attached to dorsal ligules, blunt-tipped, about 2.0 times as long as notopodial ventral ligule throughout (Fig. 13G–I). Notopodial prechaetal lobes absent. Notopodial ventral ligules narrow triangular, blunt-tipped. Neuropodial postchaetal lobes absent. Neuropodial ventral ligules narrow triangular with a pointed tip throughout; ventral cirri mid-ventrally attached to ventral edge of parapodia, blunt-tipped, about as long as ventral ligules throughout.

Notochaetae present from chaetiger 3 to posterior end, homogomph spinigers present on anterior chaetigers (Fig. 14A), homogomph falcigers present from chaetiger 16 (12–13, n=4) to posterior segments, blade with large teeth, one terminal, one lateral (Fig. 14B, C). Neurochaetae upper fascicle: homogomph spinigers present (Fig. 14D), heterogomph falcigers with serrated medium-sized blade on anterior chaetigers (Fig. 14E) and serrated shorter blade on posterior chaetigers. Neurochaetae ventral fascicle: heterogomph spinigers present (Fig. 14F), heterogomph falcigers with serrated medium-sized blade on anterior chaetigers and serrated shorter blade on posterior chaetigers (Fig. 14G). Pygidium round, one pair of filamentous anal cirri attached ventrally, about as long as last 4 (2, n=4) chaetigers (Fig. 13A).

FIG. 14. Nereis taiwanensis n. sp.; A, D, paratype ( NMNS 8174-017 ) ; B, holotype ( NMNS 8174-015 ) ; C, paratype ( NMNS 8174-018 ) ; E–G, paratype ( NMNS 8174-016 ) : A, chaetiger 9, notochaetal homogomph spiniger; B, chaetiger 16, notochaetal homogomph falciger; C, chaetiger 15, notochaetal homogomph falciger; D, chaetiger 9, neurochaetal upper fascicle, homogomph spiniger; E, same, neurochaetal upper fascicle, medium-sized blade heterogomph falciger; F, chaetiger 30, neurochaetal ventral fascicle, heterogomph spiniger; G, chaetiger 32, neurochaetal dorsal fascicle, short-bladed heterogomph falciger. Scale: A–G, 0.01 mm.

Epitokous stage: complete (NMNS 8174-019), female, body length 9.5 mm (7.5–9.0, n=3) with 39 chaetigers (40–42, n=3), beige in alcohol (Fig. 15A). Body with three regions, pre-epitokal along chaetigers 1-17 (17, n=3), natatory region from chaetiger 18 to 22 (18–22 or 18–23, n=3), posterior epitokous region from chaetiger 23 (23, 23, 24, n=3). Parapodia of pre-epitokal segments and post epitokous segments similar to atokous specimens (Fig. 15A, B). Parapodia of epitokous segments with two thin flat accessory lamellae, one between notopodial dorsal and notopodial ventral ligules, the other between notopodial ventral ligule and neuropodial ventral ligule (Fig. 15C, D). Notochaetae and neurochaetae of pre- and post-natatory regions similar to atokous specimens, replaced by swimming chaetae along natatory region segments (Fig. 15E, F). Notopodial homogomph falcigers present from chaetiger 14 to 17 (14 to 17, n=3) on pre-natatory segments and from chaetiger 24 to posterior chaetigers (23–24 to posterior chaetigers, n=3) on post epitokous segments, blade slightly bent, with one large lateral tooth distally, some with 1 to 2 additional small teeth (Fig. 15G, H).

Etymology. The name is derived from the name of the island of Taiwan where the worm was collected.

Type locality. Wonlitong , Pingtung County, Taiwan .

FIG. 15. Nereis taiwanensis n. sp.; A, B, paratype ( NMNS 8174-022); C, H, paratype ( NMNS 8174-020); D–G, paratype ( NMNS 8174-021): A, whole animal (epitokous stage; arrows indicate the natatory region); B, anterior body; C, chaetiger 15, left parapodium, anterior view; D, chaetiger 18, left parapodium, anterior view; E, chaetiger 18, swimming chaetae; F, same, swimming chaeta; G, chaetiger 26, notopodial homogomph falciger; H, chaetiger 14, notopodial homogomph falciger. (Abbreviations: DC, dorsal cirrus; FAL, flat accessory lamellae; NeVL, neuropodial ventral ligule; NoDL, notopodial dorsal ligule; NoVL, notopodial ventral ligule; VC, ventral cirrus).Scale: A, B, 1.0 mm; C, D, 0.1 mm; E, F, 0.05 mm; G, H, 0.01 mm.

Distribution. Only known from the type locality and Jihuei, Taitung County, Taiwan.

Remarks. As aforementioned, fourteen Nereis species reported from East Asia have Areas VII & VIII with 1 or 2 transverse rows of paragnaths. Of these species, only N. huanghaiensis Wu, Sun & Yang, 1981 and N. sinensis Wu, Sun & Yang, 1981 have no paragnaths on Areas I–III as in N. taiwanensis n. sp. ( Wu et al. 1981: 120, 124; Table 2). However, Nereis taiwanensis n. sp. can be readily distinguished from the former two species by having bifid blade on notopodial homogomph falcigers (versus sickle-shaped with serrations and fusiform with smooth surface, respectively) ( Wu et al. 1981: 121, 124, figs 75L, 77G; Fig. 14B, C). Moreover, both N. huanghaiensis and N. sinensis have long-bladed neuropodial heterogomph falcigers, which is not seen in N. taiwanensis n. sp. ( Wu et al. 1981: 121, 124, figs 75G, H, 77F; Fig. 14E, G).

Ecology and reproductive biology. Specimens of N. taiwanensis n. sp. examined in the present study are bycatches while the author was sampling tanaidaceans at coral reef habitats on southwest and east coasts of Taiwan. They are the smallest species of Nereis reported from Taiwan, which can reach sexual maturity with bodies smaller than 12 mm long. Five out of nine individuals collected during this present study were ovigerous females which have body length ranging from 7.5 to 11.5 mm. Of these five specimens, four are in epitokous stage (body length 7.5–9.5 mm). These ovigerous females carry relatively large eggs, with only two eggs per body segment (Fig. 15A, B).

FIG. 16. Nereis wuchiensis n. sp.; A, D, holotype ( NMNS 8174-023 ) ; B, C, paratype ( NMNS 8174-024 ) ; E, paratype ( NMNS 8174-031 ) : A, whole animal; B, pharyngeal areas, dorsal view; C, same, ventral view; D, chaetiger 11, right parapodium, anterior view; E, chaetiger 12, 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, 2.5 mm; B–E, 0.25 mm.