treatment provided by
Hesione osbornae n. sp.
( Fig. 29View FIG)
Hesione intertexta – Hoagland 1920: 604 (non Grube, 1878).
TYPE MATERIAL. — Western tropical Pacific. Holotype, USNM 18965, RV Albatross, Sta. D5355, Philippines, Palawan, North Balabac Strait , Bugsuk Island, coral and sand bottom, 2 m depth (in label; Hoagland 1920: 604 indicates 80 m depth; confirmed with the vessel database, this latter figure must be the correct depth), 5.I.1909.
ADDITIONAL MATERIAL. — Gulf of Thailand. 1 specimen, ECOSUR 291View Materials, 17View Materials km offshore (10°30’11.985”N, 100°29’45.857”E), 16 -17 m depth, muddy-shell sand, IV.2011 [11 mm long, 1 mm wide; antennae minute; eyes brownish, almost fused laterally; pharynx partially exposed; dorsal cirrosytle basally cylindrical, annulose; acicular lobe single, 1/3-¼ as long as chaetae; ventral cirri tapered, markedly longer than chaetal lobe; chaetal blades long, unidentate, guard projected beyond distal tooth].GoogleMaps
New Caledonia. 1 specimen, MNHN-IA-PNT99 (formerly jar Musorstom 649), Lagoon Est, Sta. 649 (21°51.1’S, 166°36.6’E), 64 -65 m depth, 7.VIII.1986, B. Richer coll. [28 mm long, 4 mm wide; slightly macerated, bent laterally; body without pigmentation, acicular lobe single; neurochaetal blades unidentate, guard projected beyond distal tooth].GoogleMaps
ETYMOLOGY. — This species is named after Karen Osborn, Curator of Crustacea and Polychaeta in the National Museum of Natural History, Smithsonian Institution, Washington, in recognition of her spectacular publications on bathypelagic polychaetes, and because of her enthusiastic support to our research requests. The name is a noun in genitive ( ICZN 1999: art. 31.1.2).
DISTRIBUTION. — From the Gulf of Thailand to New Caledonia, in mixed bottoms, in 2-80 m depth.
DIAGNOSIS. — Hesione with prostomium rectangular; parapodia with dorsal cirri basally cylindrical, dorsal cirrophore twice as long as wide; larger acicula blackish; acicular lobe single, tapered; neurochaetal blades unidentate, 15 times as long as wide; guards surpassing distal tooth.
Holotype, USNM 18965, complete, tapered posteriorly, without pigmentation in ethanol; some tentacular or dorsal cirri broken or lost ( Fig. 29AView FIG); right parapodia of chaetigers 8 and 13 removed (kept in vial). Body bent dorsally, 31 mm long, 5 mm wide.
Prostomium as wide as long, anterior margin truncate, lateral margins barely rounded, posterior margin deeply cleft ( Fig. 29BView FIG), about as long as ¼ prostomial length, longitudinally slightly depressed. Antennae minute, only left one remaining, oval, slightly as long as wide, 1/3 as long as interocular distance. Eyes brownish, anterior ones twice as large as, and darker than posterior ones.
Tentacular cirri long, thin, some broken, others twisted, longest ones reaching chaetigers 6-7. Lateral cushions low, divided into 2-3 sections.
Parapodia with chaetal lobes tapered, truncate ( Fig. 29C, DView FIG); dorsal cirri with cirrophores twice as long as wide, cirrostyle basally cylindrical, annulated, multiarticulated along medial and distal regions, 1/2-2/3 as long as body width; ventral cirri smooth, surpassing chaetal lobes.
Neuracicula blackish, single. Acicular lobe single, thin, tapered ( Fig. 29C, DView FIG [insets]).
Neurochaetae about 40 per bundle ( Fig. 29EView FIG), blade unidentate, blades aligned along handle, longer ones distally curved, shorter ones straight, blade size decreasing ventrally, many lost, remaining ones about 15 times as long as wide, upper chaetae with blades probably longer but twisted, each with a distal tooth and a very long guard, surpassing tooth ( Fig. 29EView FIG [insets]).
Posterior region tapered into a blunt cone ( Fig. 29FView FIG); pygidium smooth, anus with six low, cushion-like, thick papillae.
Pharynx fully exposed, rings poorly defined, 5 mm long, 3 mm wide, margin smooth, slightly eroded; dorsal papilla rounded, about as long as wide ( Fig. 29BView FIG, arrow). Oocytes not seen.
Hesione osbornae n. sp. resembles H. harrisae n. sp. because both have unidentate neurochaetal blades. However, they differ because in H. osbornae n. sp. the neurochaetal blades are about 15 times as long as wide, and guards surpass distal teeth, whereas in H. harrisae n. sp. neurochaetal blades are 6-8 times as long as wide, and guards reach the distal teeth. On the other hand, H. osbornae n. sp. resembles H. eugeniae Kinberg, 1866 because their neurochaetal blades have guards surpassing distal teeth.They differ, however, because in H.osbornae n. sp. acicular lobes are tapered, and neurochaetal blades are about 15 times as long as wide, whereas in H. eugeniae acicular lobes are digitate, and neurochaetal blades are 4-10 times as long as wide. Hesione osbornae n. sp. also resembles H. intertexta Grube, 1878 because both have tiny antennae and long neurochaetal blades, and it was previously identified as this species. However, in H. intertexta the longest blades have reduced denticles but always two are present, although the subdistal one is smaller, and the guard never extends markedly beyond the distal tooth.
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