Anobothrus dayi sp. nov.

(Figs. 4 A–J; 16A)

Specimens examined. Holotype: NSMT-Pol. H 551, Yakiuchi Bay, Amami-Oshima Island, 28°16.4'N, 129°16.5'E – 28°16.5'N, 129°16.6'E, 47– 45 m, St. 15, 7.1989. Paratype: NSMT-Pol. P 552, same locality as holotype (15cs, 3af). Paratypes: Yakiuchi Bay, NSMT-Pol. P 566, 28°16.6'N, 129°17.2'E – 28°16.6'N, 129°17.4'E, 38– 30 m, St. 16, 7.1989 (6cs); NSMT-Pol. P 567, 28°16.1'N, 129°16.2'E – 28°16.1'N, 129°16.4'E, 53– 49 m, St. 14, 7.1989 (1cs); SMF 21690, 28°16.4'N, 129°13.9'E – 28°16.4'N, 129°14.1'E, 63–71 m, St. 11, 7.1989 (7cs). Additional specimens: Off Shimoda, 34°41.0'N, 139°00.8'E – 34°40.4'N, 139°02.5'E, 106– 97 m, St. 26, 11.1981 (1af). Tosa Bay, 33°26.7'N, 133°34.8'E, 46 m, No. 2-2, 4.1970 (1cs). West of Cape Ashizuri, 32°44.3'N, 132°41.1'E – 32°44.4'N, 132°40.8'E, 124–125 m, KT-99-18, St. DG-8, 12.1999 (8cs).

Description. Length 7 mm, width 0.6 mm. Prostomium with conical middle lobe delimited by incision, without glandular ridges or eyes (Fig. 4 A, B). Buccal tentacles with ventral groove, smooth. Three pairs of cirriform branchiae in fused segment II + III (Fig. 4 C), arranged in transverse row; groups of branchiae separated by wide median gap; segmental origin of outermost and median branchiae not determinable; branchiae of segment IV inserted in innermost position of transverse row (Fig. 16 A). Chaetae in fused segments II + III originating from segment II, longer and slightly thicker than following capillaries, pointing forwards (Fig. 4 B, C, D). Chaetae of segment III absent. Notopodia with limbate capillary notochaetae from segment IV, present in 14 segments. Notopodia in fifth-to-last thoracic unciniger elevated, connected by dorsal ridge (Fig. 4 E); notochaetae of modified notopodia with broad wings and hirsute tip (Fig. 4 F). Neuropodial tori with uncini from segment VI, present in 12 thoracic uncinigers. Cirri and papillae in thoracic parapodia absent. Circular glandular band absent. Continuous ventral shields present to thoracic unciniger 9. Two intermediate uncinigers. Ten abdominal uncinigers. Rudimentary notopodia and glandular pads in intermediate and abdominal uncinigers absent. Pinnules without cirri or papillae. Pygidium with terminal anus and one pair of ventrolateral cirriform anal cirri (Fig. 4 G). Nephridial papillae absent. Thoracic uncini with 11 teeth in 2 alternating rows above rostral tooth and basal prow (Fig. 4 H, I). Abdominal uncini with crest of numerous teeth above rostral tooth and basal prow.

Remarks. No cilia are visible in the branchiae of the holotype and the larger paratypes. The smaller paratypes have branchiae with ventral tufts of cilia (Fig. 4 J). The smallest (non-type) specimens have branchiae without cilia. The development of a dorsal ridge between the elevated notopodia differs among specimens. Larger specimens usually have a more pronounced dorsal ridge.

The only other species in the genus with 3 pairs of branchiae are Anobothrus laubieri (Desbruyères, 1978) and Anobothrus flabelligerulus sp. nov. Anobothrus dayi sp. nov. differs from these species by the conical shape of the prostomium and the wide gap between the groups of branchiae. Further differences include the chaetae of segment II (paleae), which are much thinner than those of A. flabelligerulus sp. nov., and the notochaetae of segment III, which are absent in A. dayi sp. nov. and A. flabelligerulus sp. nov. but present in A. laubieri.

Etymology. The species is named after John Hemsworth Day, in recognition of his extensive research on the taxonomy of ampharetid polychaetes.

Distribution. Northwest Pacific, Japan, Sagami Bay and Tosa Bay, Pacific coast of Honshu, and Yakiuchi Bay, East China Sea coast of Amami-Oshima Island, in 30– 125 m.