Daylithos langkawiensis, 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 langkawiensis sp. nov.

Fig. 5

Material examined.

Holotype (USMCRC-Pol001): complete, south coast of Pulau Dangli , Langkawi, Malaysia (6.4473°N, 99.7774°E), 3-5 m depth, collected by SCUBA, Naoto Jimi, 11 Mar 2018 . Paratypes (USMCRC-Pol002): four specimens, complete, collected from same locality as holotype, 11 Mar 2018 .

Description.

Body 38 mm in total length (30-40 mm in paratypes), 4 mm in width (3-5 mm in width), 85 chaetigers (54-80 chaetigers in paratypes), greyish, cylindrical, tapering posteriorly into flat cauda (Fig. 5A ). Tunic thin, without sediment particles, pale. Dorsal shield flat, without depression or projection (Fig. 5B ). Body papillae minute, distally rounded, arranged in two rows per segment, posterior row papillae longer than anterior. Gonopodial lobes not seen. Neuropodial base of chaetiger 5 slightly developed.

Prostomium oval, completely covered by branchial plate (Fig. 5C ). Eyes present, blackish. Caruncle slightly exceeding the branchial plate margin. Dorsal and lateral lips present; ventral lip smaller than dorsal and lateral lips (Fig. 5D ). Palps thicker than branchiae (Fig. 5C, D ). Branchiae in two lateral groups, each with 30 filaments. Longest branchiae in inner rows slightly longer than outer rows. Nephridial lobes not seen.

Cephalic cage chaetae about 2/7 body length, four times as long as body width (Fig. 5A, B ). Chaetiger 1-2 comprising cephalic cage; chaetiger 1 with 8 notochaetae and 10 neurochaetae per side; chaetiger 2 with 6 notochaetae and 8 neurochaetae per side. Chaetiger 1 two times longer than chaetiger 2. Chaetae of chaetiger 3 three 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, 1/5 maximum body width, 2-4 per bundle, with approximately 90 articles (Fig. 5E ); articles medium-sized distally (20 times as long as wide) (Fig. 5F ), short medially and basally (2/3 times as long as wide) (Fig. 5G ). Neurochaetae multi-articulated aristate capillaries in chaetigers 1 to 7, aristate capillaries, 3 per bundle. Neurohooks present in chaetiger 8, arranged in short transverse rows, golden (Fig. 5H, I ), 2-4 per ramus in anterior chaetigers, 2-6 in posterior chaetigers, curved, articles very short, anchylosed.

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

Oocytes inside middle part of body, blackish in ethanol.

Etymology.

this species is named after the type locality, Langkawi.

Distribution.

shallow subtidal area of Langkawi Island, Malaysia; 3-5 m depth;

Corals as hosts of the new species are not restricted to specific species (mainly found from Faviidae ).

Remarks.

Daylithos langkawiensis sp. nov. resembles D. iris (Michaelsen, 1892), D. japonicus sp. nov. and D. amamiensis sp. nov. in having a greyish body in fixed material, 2-6 neurohooks on far posterior chaetigers and flat dorsal shield as opposed to with depression. While neurohooks of the new species are present from chaetiger 8, the neurohooks of Daylithos iris are present from chaetiger 10; D. japonicus is from chaetiger 8; and D. amamiensis is from chaetiger 7. Eyes present in the new species, while absent in D. iris . Anterior row of body papillae in D. langkawiensis sp. nov. are shorter than posteriorones; in D. amamiensis sp. nov., are longer than posterior ones; anterior ones in D. japonicus and the new species are similar in size to posterior rows; 5-8 neurohooks present in posterior chaetigers of D. japonicus , while 2-6 neurohooks in posterior chaetigers of D. langkawiensis .

Figures

Figure 5. Daylithos langkawiensis sp. nov. Holotype (USMCRC-Pol 001). A. Whole body, lateral view; B. Anterior end, lateral view; C. Prostomium, lateral view, covered by branchial plate; D. Prostomium, frontal view; E. Notochaetae, chaetiger 12; F. Distal part of notochaetae; G. Basal part of notochaetae; H. Neurohook, chaetiger 12; I. Middle part of neurohook. 5 mm (A, B); 1 mm (C, D); 200 μm (E); 100 μm (F); 200 μm (G); 100 μm (H); 50 μm (I). Abbreviations: bp, branchial plate; br, branchiae; p, palp; dl, dorsal lip; ll, lateral lip.