(Figs. 2 A–L; 6 B)
Specimens examined. Holotype NSMT-Pol. H 547, Tokyo Bay, 35 ° 22.6 ’N, 139 ° 45.4 ’E, 20 m, KT- 71 - 12, St. TB, 8.1971. Paratypes: NSMT-Pol. P 548, same locality as holotype (59 cs). SMF 21642, Tokyo Bay, 35 °23.0’N, 139 °45.0’E, 20 m, KT- 71 - 19, St. B 5, 11.1971 (3 cs). Additional specimens: Utoro, Hokkaido, 44 °05.1’N, 145 °00.1’E, intertidal zone, 8.1960 (1 af). Sarufutsu, Hokkaido, 45 ° 19.3 ’N, 142 ° 14.8 ’E, 22 m, NSMT, St. 14, 9.1991 (1 af). Tobetsu, Hokkaido, 41 ° 44.3 ’N, 140 ° 35.6 ’E, intertidal zone, 8.1963 (1 af). Otsuchi Bay, 39 ° 20.7 ’N, 141 ° 57.5 ’E – 39 ° 20.6 ’N, 141 ° 57.6 ’E, 45 m, St. 5, 10.1978 (1 af). Kamaishi Bay, 39 ° 14.9 ’N, 141 °55.0’E, 31 m, St. 6, 11.1974 (8 cs, 9 af). Ofunato Bay, 39 °01.4’N, 141 ° 43.2 ’E, 10 m, St. 3, 7.1967 (1 af). Banzu, 35 ° 24.5 ’N, 139 ° 53.9 ’E, 4 m, St. 9, 6.1974 (1 cs, 2 af); Off Toi, Suruga Bay, 34 ° 55.1 ’N, 138 ° 44.1 ’E – 34 ° 54.2 ’N, 138 ° 44.1 ’E, 313 – 304 m, KT- 73 - 15, St. H, 10.1973 (1 cs). Tsukumo Bay, 37 ° 17.7 ’N, 137 ° 14.7 ’E – 37 ° 17.9 ’N, 137 ° 14.7 ’E, 37 m, St. 4, 5.1973 (2 cs, 3 af; SMF 21689). Mukaishima, 34 ° 21.7 ’N, 133 ° 13.2 ’E, intertidal zone, 5.1964 (1 af). Ariake Sea, 32 ° 37.6 ’N, 130 ° 17.2 ’E, 19 m, St. 67, 12.1957 (1 cs). Tomioka Bay, Amakusa, 32 °32.0’N, 130 °03.5’E, 27 m, 12.1962 (2 cs).
Description. Length 20 mm, width 2 mm. Prostomium with middle lobe delimited by incision, without glandular ridges or eyes (Fig. 2 A). Buccal tentacles unknown. 4 pairs of annulated, cirriform branchiae in fused segments II + III; 3 pairs of branchiae in transverse line without median gap, 4 th pair shifted caudally between 2 nd outermost and innermost branchiae of transverse row; branchiae of segment II in 2 nd outermost position of transverse row, branchiae of segment III in outermost position of transverse row, branchiae of segment IV in innermost position of transverse row, branchiae of segment V shifted caudally (Figs. 2 B; 6 B). Chaetae in fused segments II + III absent. Notopodia with limbate capillary notochaetae from segment IV, present in 14 chaetigers (Fig. 2 C). Neuropodial tori with uncini from segment VI, present in 12 thoracic uncinigers. Cirri and papillae in thoracic parapodia absent (Fig. 2 D, E). Very well developed continuous ventral shields present to thoracic unciniger 11, weakly developed ventral shields in thoracic unciniger 12. Elevated or modified notopodia absent. 2 intermediate uncinigers. 15 abdominal uncinigers. Well developed glandular pads with well set off terminal papilla above tori of intermediate segments and above pinnules in abdominal segments. Pinnules with well developed dorsal papilla (Fig. 2 F, G). Pygidium with terminal anus, surrounded by 1 pair of lateral, cirriform anal cirri, inserted sub-terminally, and a ring of papillae (Fig. 2 H). 1 pair of distinct nephridial papillae in segment IV, located posterior to innermost branchiae of transverse row. Thoracic uncini with 7 teeth in 2 alternating rows above basal prow and rostral tooth (Fig. 2 I, J). Abdominal uncini with 8 teeth in 2 alternating rows above basal prow and rostral tooth (Fig. 2 K, L). Distinct reddish brown stripe along body on both sides, located between notopodia and tori in thorax (Fig. 2 E) and continuing in glandular pads of intermediate and abdominal segments; terminal papillae of glandular pads unpigmented; prostomium, peristomium, and ventral shields with less distinct brown pigmentation.
Remarks. Ampharete cinnamomea sp. nov. belongs to the rather small group of Ampharete species without notochaetae in the fused segments II + III, formerly assigned to the genus Asabellides Annenkova, 1929. The species described here has 15 abdominal segments, while the other Ampharete species without notochaetae in the fused segment II + III have either less abdominal segments – A. cornuata (Hilbig, 2000) with 8, A. californica (Hilbig, 2000) with 9, A. lineata (Berkeley and Berkeley, 1943) with 12 – or more abdominal segments – A. sibirica (Wirén, 1883) with 18, A. orientalis (Annenkova, 1929) with 19. Ampharete cinnamomea sp. nov. also differs from A. californica, A. cornuata, and A. lineata by lacking a median gap between left and right groups of branchiae. Further differences are the filiform dorsal cirri in the neuropodia of intermediate and abdominal uncinigers of A. lineata, horn-like anterolateral extensions of the prostomium in A. cornuata, the unusually fused branchiae and very large nephridial papillae in A. orientalis, and the very short anal cirri in A. sibirica.
Etymology. The species name refers to the distinct lateral brown pigmentation, which is reminiscent of cinnamon sprinkles.
Distribution. Hokkaido, northern and southern Honshu and Kyushu. The species has been found from the intertidal to 304 m, and is dominant in 20 m depth in Tokyo Bay.