Daylithos japonicus, Jimi & Fujita & Woo, 2023

Jimi, Naoto, Fujita, Toshihiko & Woo, Sau Pinn, 2023, Four new species of coral- and rock-boring polychaetes Daylithos (Annelida, Flabelligeridae) from the Pacific Ocean, Zoosystematics and Evolution 99 (1), pp. 149-159 : 149

Daylithos japonicus sp. nov.

Fig. 2

Type material.

Holotype (NSMT-Pol H-903): complete, collected in front of Kuroshio Biological Research Institute (32.7787°N, 132.7326°E), Kochi, 10 m depth, SCUBA, Naoto Jimi, 12 Oct 2017. Paratype (NSMT-Pol P-904): six specimens, complete, collected with holotype, 12 Oct 2017. Paratypes (NSMT-Pol P-905): 10 specimens, complete, collected from Hakamagoshi (31.5907°N, 130.5922°E), Kagoshima, 5-15 m depth, by SCUBA, Naoto Jimi, 17 Nov 2016. Paratypes (NSMT-Pol P-906): three specimens, complete, collected from Shirahama (33.6918°N, 135.3360°E), Wakayama, 5-10 m depth, by SCUBA, Naoto Jimi, 25 Aug 2016.

Description

(based on holotype). Body 40 mm in total length (17-40 mm in paratypes), 4 mm in width (2-5 mm in paratypes), 94 chaetigers (70-91 chaetigers in paratypes), greyish, cylindrical, tapering posteriorly into flat cauda (Fig. 2A ). Tunic thin, without sediment particles, greyish. Dorsal shield flat, without depression or projection (Fig. 2B ). Body papillae minute, distally rounded, arranged in two rows per segment, anterior row with more papillae. Gonopodial lobes not seen. Neuropodial base of chaetiger 5 slightly swollen.

Prostomium oval. Eyes present, blackish. Caruncle slightly exceeding the branchial plate margin. Dorsal and lateral lips present (Fig. 2C, D ); ventral lip smaller than dorsal and lateral lips. Palps thicker than branchiae. Branchiae in two lateral groups, each with 20 filaments. Longest branchiae in inner rows, about half as long as palps, decreasing in length towards lateral margins (Fig. 2C ). Nephridial lobes not seen.

Cephalic cage chaetae about 3/8 body length, four times as long as body width (Fig. 2B ). Chaetiger 1-2 comprising cephalic cage; chaetiger 1 with 8 notochaetae and 7 neurochaetae per side; chaetiger 2 with 7 notochaetae and 7 neurochaetae per side. Chaetiger 1 1.1 times longer than chaetiger 2. Chaetae of chaetiger 3 two times longer than the following ones. Chaetal transition from cephalic cage to body chaetae abrupt.

Notopodia poorly developed, lateral; neuropodia ventrolateral in median body. Notopodia and neuropodia widely separated. Parapodial lobes absent. Notochaetae multi-articulated capillaries, transparent, 1/4 maximum body width, 3-4 per bundle, with about 90 articles (Fig. 2E ); articles medium-sized distally (20 times as long as wide) (Fig. 2F ), short medially and basally (two times as long as wide) (Fig. 2G ). Neurochaetae multi-articulated, aristate capillaries in chaetigers 1 to 7, 3 per bundle. Neurohooks present from chaetiger 8 (Fig. 2H ), arranged in short transverse rows, golden, 1-4 per ramus in anterior chaetigers, 5-8 in posterior chaetigers, subdistally wider, tip slightly curved. 6-7 articles (two times as long as wide).

Posterior end depressed; pygidium with anus terminal, anal cirri absent.

Oocytes inside middle part of body, brackish in ethanol.

Etymology.

The specific name japonicus is a Latin adjective, referring to the occurrence of the new species in Japan.

Distribution.

Southern Japan, shallow subtidal areas; 3-15 m depth; in burrows within corals. Corals as hosts of the new species are mainly found from Faviidae .

Remarks.

Daylithos japonicus sp. nov. resembles D. iris (Michaelsen, 1892) in having the greyish body in fixed material, 5-8 neurohooks on far posterior chaetigers and the flat dorsal shield ( Michaelsen 1892; Salazar-Vallejo 2012). These species differ because, in D. japonicus , neurohooks are present from chaetiger 8 onwards, but, in D. iris , they start in chaetiger 10. The cephalic cage of D. japonicus is 3/8 of body length, while D. iris is 1/8 of body length. Eyes are present in the new species, while absent in D. iris . On the other hand, D. japonicus resembles D. parmatus in having a greyish body and many neurohooks on far posterior chaetigers; however, in D. japonicus , the dorsal shield is flat and there are 5-8 neurochaetae in posterior chaetigers, whereas in D. parmatus , the dorsal shield is cleft and has 4-7 neurochaetae in posterior chaetigers.

Japanese Daylithos , which is called “Minamihabouki” has been recorded as D. parmatus in Japan ( Fauvel 1936; Imajima and Hartman 1964; Uchida 1992). In this study, it turned out that D. parmatus reported from Japan is a misidentification and actually is D. japonicus , the present new species (see Discussion).

Figures

Figure 2. Daylithos japonicus sp. nov. Holotype (NSMT-Pol H- 903). A. Whole body, lateral view; B. Anterior end, lateral view; C. Prostomium, frontal view; D. Prostomium, lateral view; E. Notochaetae, chaetiger 12; F. Distal part of notochaetae; G. Basal part of notochaetae; H. Neurohook, chaetiger 12. Scale bars: 5 mm (A); 2.5 mm (B); 0.5 mm (C); 0.1 mm (D); 200 μm (E); 100 μm (F); 100 μm (G); 200 μm (H). Abbreviations: cc, cephalic cage; lb, large branchia; sb, small branchia; p, palp; dl, dorsal lip; ll, lateral lip; vl, ventral lip.