Daylithos amamiensis, 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 amamiensis sp. nov.

Fig. 3

Type material.

Holotype (NSMT-Pol H-907): collected from Shirahama, Amami Oshima (28.1970°N, 129.2699°E), 5 m depth, SCUBA, Naoto Jimi, 15 Nov 2016. Paratype (NSMT-Pol P-908): one specimen, middle chaetigers lost, collected from same locality as holotype, 15 Nov 2016.

Description

(based on holotype). Body 30 mm in total length (24 mm in paratype), 3 mm in width (3 mm in paratype), 47 chaetigers (posterior chaetigers lost) (67 chaetigers in paratype), greyish, cylindrical (Fig. 3A ). Body tapering posteriorly into flat cauda (paratype) (Fig. 3A ). Tunic thin, without sediment particles, blackish. Dorsal shield flat, without depression or projection (Fig. 3B ). Body papillae minute, distally rounded, arranged in two rows per segment; anterior row papillae longer than posterior. Gonopodial lobes absent. Neuroparapodial base of chaetiger 5 slightly swollen.

Prostomium oval. Eyes present, blackish. Caruncle slightly exceeding the branchial plate margin, with black pigments. Dorsal and lateral lips present (Fig. 3C, D ); ventral lip smaller than dorsal and lateral lips. Palps thicker than branchiae. Branchiae in two lateral groups, each with 35 filaments. Longest branchiae in inner rows, about half as long as palps, decreasing in length towards the lateral margins (Fig. 3C ). Nephridial lobes not seen. Larger branchiae three times wider than smaller branchiae.

Cephalic cage chaetae about three times longer than body width (Fig. 3A ). Chaetiger 1-2 comprising cephalic cage (Fig. 3B ); chaetiger 1 with 7 notochaetae and 8 neurochaetae per side; chaetiger 2 with 5 notochaetae and 6 neurochaetae per side. Chaetiger 1 1.5 times longer than chaetigers 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 (Fig. 3E ), transparent, 1/4 maximum body width, 2-3 per bundle, with about 110 articles; articles medium-sized distally (12 times as long as wide), short medially and basally (1/2 times as long as wide) (Fig. 3F ). Neurochaetae multi-articulated aristate capillaries in chaetigers 1 to 6, 3 per bundle. Neurohooks present in chaetiger 7, arranged in short transverse rows, golden colour (Fig. 3G, H ), 1-4 per ramus in anterior chaetigers, 4-6 in posterior chaetigers, curved. About 30 anchylosed articles in larger hooks.

Posterior end depressed; pygidium with anus terminal, without anal cirri.

Oocytes inside middle part of body, blackish in ethanol.

Etymology.

This species is named after the type locality, Amami Oshima.

Distribution.

This species is only known from the type locality, 5 m in depth, Shirahama, Amami-Oshima, Japan; found in burrows within corals ( Acroporidae ).

Remarks.

Daylithos amamiensis sp. nov. resembles D. iris (Michaelsen, 1892) and D. japonicus sp. nov. in having the greyish body in fixed material, 4-6 neurohooks on far posterior chaetigers and the flat dorsal shield. While neurohooks of D. amamiensis are present from chaetiger 7, those of D. iris are from chaetiger 10; and in D. japonicus , are from chaetiger 8. Eyes are present in D. amamiensis , but absent in D. iris . Further, in D. amamiensis , the body papillae in the anterior row are longer than posterior ones; whereas those in D. japonicus are similar size to posterior ones.

Figures

Figure 3. Daylithos amamiensis sp. nov. Holotype (NSMT-Pol H- 907). A. Whole body, lateral view (insert: posterior end of paratype); B. Anterior end, lateral view; C Prostomium, frontal view; D. Prostomium, lateral view; E. Notochaetae, chaetiger 12; F. Basal part of notochaeta; G. Neurohook, chaetiger 12; H. Middle part of neurohook. Scale bars: 10 mm (A, B); 2.5 mm (A (insert )); 2 mm (C, D); 200 μm (E); 100 μm (F); 200 μm (G); 100 μm (H). Abbreviations: cc, cephalic cage; ca, caruncle; lb, large branchia; sb, small branchia; p, palp; dl, dorsal lip; ll, lateral lip; vl, ventral lip.