Five New Species of Flabelligera (Flabelligeridae: Annelida) from Japan Author Jimi, Naoto Sugashima Marine Biological Laboratory, Graduate School of Science, Nagoya University, 429 - 63 Sugashima, Toba, Mie 517 - 0004, Japan E-mail: beniimo 7010 @ gmail. com & Centre for Marine & Coastal Studies, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia & Corresponding author beniimo7010@gmail.com Author Hasegawa, Naohiro Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060 - 0810, Japan Author Taru, Masanori Tokyo Bay Ecosystem Research Center of Toho University, Funabashi, Chiba 274 - 8510, Japan Author Oya, Yuki College of Arts and Sciences, J. F. Oberlin University, Machida, Tokyo 194 - 0294, Japan Author Kohtsuka, Hisanori Misaki Marine Biological Station, School of Science, The University of Tokyo, Miura, Kanagawa 238 - 0225, Japan Author Tsuchida, Shinji Research Institute for Global Change RIGC, Japan Agency for Marine-Earth Science and Technology JAMSTEC, Yokosuka, Kanagawa 237 - 0061, Japan Author Fujiwara, Yoshihiro Research Institute for Global Change RIGC, Japan Agency for Marine-Earth Science and Technology JAMSTEC, Yokosuka, Kanagawa 237 - 0061, Japan Author Woo, Sau Pinn Centre for Marine & Coastal Studies, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia text Species Diversity 2022 2022-04-15 27 1 101 111 http://dx.doi.org/10.12782/specdiv.27.101 journal article 10.12782/specdiv.27.101 2189-7301 7175308 7D22B9BE-813C-478E-8D14-37E578BF157B 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. Fig. 5. Flabelligera kozaensis sp. nov. , holotype (NSMT-Pol H-875). A, Whole body, lateral view, in live; B, anterior end, ventral view, in live; C, prostomium, frontal view; D, notochaetae, chaetiger 12; E, distal part of notochaetae; F, enlarged view of middle part of notochaetae; G, basal part of notochaetae; H, neurohook, chaetiger 12; I, enlarged view of middle part of neurohook. Scale bars: A, B, 1 cm; C, 1 mm; D, 200µm; E, 100µm; F, 50µm; G, H, 200µm; I, 100µm. Abbreviations: bs, branchial scar; ca, caruncle; cc cephalic cage; dp, dorsal side elevation of palp base; e, eye; ll, lateral lip; ps, palp scar. 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, 1 cm; B, C, 5 mm; D, 200µm; E, 100 µm; 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. Table 1. K2P genetic distances of Flabelligera spp. in this study.

Species	1	2	3	4	5	6	7	8
1. F. japonica sp.nov.
2. F. kaimeiae sp.nov.	0.2117
3. F. kozaensis sp.nov.	0.21447	0.22629
4. F.kajiharai sp.nov.	0.19357	0.13452	0.25549
5. F.sekii _ sp. nov. from Rausu	0.17299	0.1214	0.21959	0.10517
6. F.sekii _ sp. nov. from Daikokujima	0.17098	0.1214	0.22181	0.10517	0.00158
7. F. affinis sensu Carr et al. (2011)	0.18947	0.1197	0.22197	0.10185	0.09479	0.09664
8. F.infundibularis sensu Osborn and Rouse (2008)	0.18568	0.18126	0.22348	0.17986	0.17731	0.17937	0.17986

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%.