Nereis articulata, Hsueh, 2020

Hsueh, Pan-Wen, 2020, New species of Nereis (Annelida, Polychaeta, Nereididae) from Taiwanese waters, Zootaxa 4802 (1), pp. 1-31 : 4-6

Nereis articulata n. sp.

Figs 1A–F, 2A–G

Material examined. Holotype ( NMNS 8174-001 ), Wuchi Port (24°17.61ʹN 120°31.18ʹE), Taichung City, Taiwan, subtidal fouling community on cement surfaces of piers, 5 October 2015.

Description. Holotype (NMNS 8174-001), incomplete, posterior end missing, remaining body length 26.0 mm with 47 chaetigers, maximum width 1.5 mm at chaetiger 4, excluding parapodia; light brown in alcohol (Fig. 1A). Prostomium wider than long, lateral antennae antero-lateral, longer than palps, ceratostyles articulated; palpophores globose, palpostyles conical, four pairs of tentacular cirri, longest one reaching chaetiger 3, longest tentacular cirri with 4–5 distal articulations, shortest tentacular cirri with 2 distal articulations (Fig. 1B, C). Two pairs of eyes, in trapezoidal arrangement, subequal in size. Apodous anterior segment about 1.7 times as long as chaetiger 1. Pharynx with light brown jaws, each with 7–8 teeth; I=1; II=24 (left), 24 (right), in 3–4 oblique rows; III=8, in 2 transverse rows; IV=23 (left), 27 (right), in 3–4 oblique rows; V=0; VI=16 (left), 14 (right), in a cluster; VII/VIII=198, in 6–7 rows (Fig. 1D).

Notopodial dorsal ligules digitiform throughout, gradually shorter and smaller on posterior chaetigers (Fig. 1E, F). Dorsal cirri basally attached to dorsal ligules, about 3.0 times as long as dorsal ligules throughout (Fig. 1E, F). Notopodial prechaetal lobe absent. Notopodial ventral ligules digitiform throughout, gradually shorter and smaller on posterior chaetigers. Neuropodial postchaetal lobe absent. Neuropodial ventral ligules digitiform throughout; ventral cirri mid-ventrally attached to ventral edge of parapodia, about as long as ventral ligules (Fig. 1E, F).

Notochaetae present from chaetiger 3 to posterior segments, homogomph spinigers present on anterior chaetigers (Fig. 2A), homogomph falcigers present from chaetiger 21 to posterior segments, blade strongly bent subdistally, blunt-tipped, margin with 1 large lateral tooth and 1 or 2 smaller teeth (Fig. 2B), tip of blade sometimes broken off (Fig. 2C). Neurochaetae upper fascicle: homogomph spinigers present (Fig. 2D), heterogomph falcigers with serrated long-blade (Fig. 2E). Neurochaetae ventral fascicle: heterogomph spinigers present (Fig. 2F), heterogomph falcigers with serrated long-blade (Fig. 2G).

Etymology. The name refers to the presence of articulations on tentacular cirri of the animal.

Type locality. Wuchi fishing port, Taichung City, Taiwan .

Distribution. Only known from the type locality.

Remarks. Nereis articulata Ehlers, 1887 , a senior homonym, has been considered invalid. Hartmann-Schröder (1985) transferred this species to the genus Ceratonereis Kinberg, 1865 and placed it in the subgenus Composetia Hartmann-Schröder, 1985 , as it has notopodial homogomph falcigers. However, Bakken & Wilson (2005) com- mented that members of that subgenus do not have notopodial homogomph falcigers. Nereis articulata n. sp. can be readily distinguished from the other 35 Nereis species reported from East Asia and the present study by having an articulated tentacular cirri, which is not seen in other congeners.

FIG. 1. Nereis articulata n. sp.; holotype (NMNS 8174-001): A, whole animal; B, anterior body; C, close-up of anterior body (arrow points articulations of long tentacular cirrus); D, paragnaths of the maxillary and oral rings; E, chaetiger 10, right parapodium, posterior view; F, chaetiger 47, right parapodium, posterior 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–D, 0.5 mm; E, F, 0.25 mm.

FIG. 2. Nereis articulata n. sp.; holotype (NMNS 8174-001): A, chaetiger 43, notochaetal homogomph spiniger; B, same, notochaetal homogomph falciger; C, chaetiger 11, notochaetal homogomph falciger; D, same, neurochaetal upper fascicle, homogomph spiniger; E, same, neurochaetal upper fascicle, long-bladed heterogomph falciger; F, same, neurochaetal ventral fascicle, heterogomph spiniger; G, same, neurochaetal ventral fascicle, long-bladed heterogomph falciger. Scale: A, D, F, 0.025 mm; B, C, E, G, 0.01 mm.