Flabelligera sekii Jimi, 2022

Jimi, Naoto, Hasegawa, Naohiro, Taru, Masanori, Oya, Yuki, Kohtsuka, Hisanori, Tsuchida, Shinji, Fujiwara, Yoshihiro & Woo, Sau Pinn, 2022, Five New Species of Flabelligera (Flabelligeridae: Annelida) from Japan, Species Diversity 27 (1), pp. 101-111 : 107-110

Flabelligera sekii Jimi , sp. nov.

[Japanese name: Seki-kanten-habouki] ( Fig. 6 )

Material examined. Holotype (NSMT-Pol H-877): 60 mm long, 8 mm wide, 38 chaetigers, complete body, Rausu , Hokkaido, Japan (44°2′6″N, 145°13′35″E), 5 m depth, 23 March 2018, collected by Naoto Jimi. Paratypes: 1 specimen (NSMT-Pol P-878), 45 mm long, 7 mm wide, 35 chaetigers, complete body, collected with the holotype; 1 specimen (NSMT-Pol P-879), 40 mm long, 7 mm wide, 32 chaetigers, Daikokujima Island , Hokkaido (42°57′32″N, 144°52′32″E), intertidal, 26 June 2017, complete body, collected by Naoto Jimi .

Description. Body tapered posteriorly ( Fig. 6A ). Tunic thick, opaque, densely papillated, with sediment particles. Sediment particles cover all of notochaetal and half of neurochaetal lobes. Body papillae long, thin, digitate. Gonopodial lobes not seen.

Cephalic cage chaetae about 1/12 body length, as long as body width ( Fig. 6B ). Chaetiger 1 comprising cephalic cage; chaetiger 1 with 32 notochaetae and 20 neurochaetae per side. Chaetiger 1 longer than chaetigers 2–3. Chaetal transition from cephalic cage to body chaetae abrupt, chaetiger 2 with multiarticulated neurohooks.

Prostomium rounded. Brown eyes present, two pairs, anterior eyes larger than posterior ones ( Fig. 6C ). Caruncle developed, wide, exceeding branchial plate margin, distally blunt ( Fig. 6C ). Lateral lips developed, fused to dorsal lip ( Fig. 6C ). Ventral lip triangular, without ventral projection. Palps pale, thick, slightly longer than branchiae, about four times thicker than branchiae. Palp scars rounded, elevated ( Fig. 6C ). Branchiae in two lateral groups, each with filaments in concentric rows, each group with 80 filaments. Nephridial lobes paired, lateral to caruncle, about the median distance of branchial groups.

Parapodia developed, lateral; median neuropodia ventrolateral. Notopodial lobes projected, digitate, exceeding half of notochaetae, without different papillae. Neuropodial lobes projected, digitate, without different papillae. Noto- and neuropodia widely separated. Notochaetae multiarticulated capillaries, transparent, 1/2 body width, 10 per bundle, with approximately 250 articles; articles short throughout chaetae, gelatinous cover present throughout notochaetae. ( Fig. 6D–F ). Neurochaetae multiarticulated capillaries in chaetiger 1. Multiarticulate neurohooks present in chaetiger 2 and succeeding posterior chaetigers, black, one or two per ramus, with 5 medium sized articles medially, other articles anchylosed, articles absent in basally. Crest slightly wider than handle, width: length ratio 1: 6 ( Fig. 6G–I ).

Posterior end truncated; pygidium with anus terminal, not covered by tunic, thick muscular ring, without anal cirri.

Etymology. The species is named after Mr. Katsunori Seki. He is a specialist in diving under ice-locked sea and helped collection of this new species.

Remarks. This species resembles F. bophortica , F. japonica sp. nov., and F. kajiharai sp. nov. in having body without transverse bands, opaque tunic with fine sediments, one articulated neurohook per parapodia from chaetiger 2, and neurohooks with long crests ( Annenkova-Chlopina 1924; Salazar-Vallejo 2012). The species F. sekii sp. nov. can be discriminated from the three species by having two neurohooks per parapodium, black crest of neurohook, and tunic covering notochaetal lobes, while the other three species have only one neurohook per parapodium, neurohooks with golden crests, and notochaetal lobes without tunic cover.

Genetic distances. K2P genetic distances for the COI sequences ( Table 1) showed distances among the six Flabelligera species ranging from 9.4 to 25.5%. The lowest interspecific genetic distance is 9.4% between F. affinis sensu Carr et al. (2011) and F. sekii from Rausu. The intraspecific genetic distance between F. sekii from Rausu and F. sekii from Daikokujima is 0.1%.

Figures

Fig. 6. Flabelligera sekii sp. nov., holotype (NSMT-Pol H-877). A, Whole body, dorsal view; B, anterior end, dorsal view; C, prostomium, frontal view; D, notochaetae, chaetiger 12; E, middle to distal part of notochaetae; F, distal part of notochaetae; G, neurohook, chaetiger 12; H, distal part of neurohook; I. middle part of neurohook. Scale bars: A, 1cm; B, C, 5mm; D, 200µm; E, 100µm; F, 50µm; G, 200µm; H, 100µm; I, 100µm. Abbreviations: bp, branchial scar; ca, caruncle; cc, cephalic cage; dL, dorsal lip; e, eye; ll, lateral lip; ps, palp scar.