Hesione horsti Salazar-Vallejo 2018, n. sp.

Hesione horsti n. sp.

(Figs 21, 22)

urn:lsid:zoobank.org:act: 58221603-3923-4EA5-AFDF-3E05B2196059

Hesione intertexta – Horst 1924: 192-193 (partim, non Grube, 1878).

TYPE MATERIAL. — Indonesia. Holotype, RMNH 19913, East Timor, South coast, at anchorage, RV Siboga Exped. Stat. 285 (08°39.1’S, 127°04.4’E), 34 m depth, dredge, muddy bottom and coral, 18.I.1900.

ADDITIONAL MATERIAL. — Indonesia. Four specimens, RMNH 431.4, Sulawesi, RV Siboga Exped. Stat. 205, Buton Strait, Lohio Bay, 22 m depth, dredge, sand, muddy bottom, 20.IX.1899 [15-20 mm long, 1-2 mm wide; colorless, even aciculae being honey-colored instead of blackish; integument smooth; acicular lobe single; neurochaetal blades variable in length, upper ones longer, bidentate, teeth minute, directed upwards, smaller ones in a lower position, bidentate, subdistal tooth smaller or as large as distal one, guard approaching subdistal tooth, rarely approaching distal tooth]. — 1 specimen, RMNH 431.5, Irian Jaya, RV Siboga Exped. Stat. 273, Aru Islands (06°10’S, 134°30’E), Pearl Banks, anchorage off Pulu Jedan, 13 m depth, trawl, dredge and divers, sand and shells, 23-26.XII.1899 [23 mm long, 2 mm wide; macerated, many neurochaetal blades lost; integument smooth; acicular lobe single, tapered; neurochaetal blades bidentate, guard approaching distal tooth]. — 2 specimens, RMNH 1277, Sulawesi, RV Siboga Exped. Stat. 213, Saleyer (Selayar Island, 06°00’00”S, 120°30’00”E), anchorage, 36 m depth, coral reef expl., muddy bottom, sand, 26 Sep.1899 [27-36 mm long, 4-5 mm wide; dorsal surface rugose].

Papua New Guinea. 1 specimen, AM 48557, North side of Rasch Pass, Madang, coral substrate, 3.VII.1987, P. A. Hutchings coll. [25 mm long, 3 mm wide; complete, slightly macerated; midventral longitudinal depression reddish; anterior eyes as long as wide; pygidium granulose, reddish; acicular lobe single; blades bidentate, guard approaching distal tooth; dorsal cirrophore short; ventral cirri articulated].

Australia. 2 specimens, AM W.2938, Great Barrier Reef Expedition, Sta. 14, Queensland, 1.2 km SE off Lizard Island, 35 m, Great Barrier Reef Expedition, 9.III.1929 [29-30 mm long, 3-4 mm wide; bent laterally, integument smooth to annulated, right parapodium of chaetiger 10 removed from 1 specimen, and right parapodium of chaetiger 3 and left one from chaetiger 14 of the other, removed for observation (kept in separate vials); anterior eyes as long as wide (set at the prostomial margin), about twice larger than posterior ones; acicular lobe single, tapered; neurochaetal blades bidentate, anterior chaetigers and upper bundle chaetae with long blades, teeth small, directed distally, others with teeth larger, directed laterally, guard approaching distal tooth]. — 1 specimen, AM G.11250, Port Molle, Queensland, no further data [dried-out, stiff, dark gray, bent laterally, integument smooth, most tentacular and dorsal cirri lost, most chaetal blades lost, body 5 mm long, 1.2 mm wide; prostomium distorted; antennae tapered, 3-4 times as long as wide; anterior eyes marginal, as long as wide, twice larger than posterior ones; acicular lobe single, tapered; chaetal blades not seen, parapodia not dissected to avoid further damage]. — 1 specimen, BMNH 1931.7.1.21, Great Barrier Reef Expedition 1929, N Direction Island, no further data [body slightly bent dorsally, integument smooth, some dorsal cirri lost, most without tips; right parapodia of chaetigers 8 and 9 previously removed; body 32 mm long, 3 mm wide; prostomium as long as wide; antennae tapered, 3-4 times as long as wide; anterior eyes marginal, as long as wide, twice larger than posterior ones; acicular lobe single, tapered; chaetal blades not seen, parapodia not dissected to avoid further damage]. — 1 specimen, ZMB 5280, Hamurger SW-Australien Expedition 1905, SW Australia, Sharks Bay, 10 km S Denham, Sta. 8, 1905, Michaelsen & Hartmeyer coll. [18 mm long, 2 mm wide; slightly distorted, partially dehydrated; integument smooth, except in pygidium; antennae digitate, 4 times as long as wide, longer than interocular distance; anterior eyes as long as wide, of the same width than posterior ones; neuraciculae blackish, tapered; acicular lobe single, basally swollen, tip tapered; neurochaetae about 20 per bundle; blades bidentate, upper chaetae with smaller teeth; guard approaching distal tooth; pygidium granulose].

Japan. 1 specimen, NHMW 576, Enoshima, 1877, Drasche coll. [40 mm long, 5.5 mm wide; partially dehydrated; body pale brown without pigmentation pattern; pharynx exposed; antennae minute, smaller than posterior eyes diameter; acicular lobe single, massive, tips probably eroded; most neurochaetal blades broken; lateral cushions dehydrated, with longitudinal wrinkes resembling granular surface as seen in other specimens]. — 1 specimen, SMF 11220, Boso Peninsula, Katsuura, Yoshia, subtidal rocky shore, 4.VI.1998, E. Nishi coll. [69 mm long, 7 mm wide; colorless; slightly distorted, most tentacular and dorsal cirri lost; many chaetal blades lost, right parapodia of chaetigers 2 and 9 removed for observation (kept in vial); antennae digitate as long as interocular distance, or 3-4 times as long as wide; anterior eyes larger than posterior ones; integument smooth, lateral cushions smooth, entire; acicular lobes single, blunt, basally swollen; neurochaetal blades bidentate, distal tooth larger, guards mostly eroded, approaching subdistal tooth]. — 1 specimen, SMF 14026, Izu Peninsula, Shiduoka, Shimoda, intertidal, sandy bottom, 16.X.2002, E. Nishi coll. [32 mm long, 5.5 mm wide; colorless, most dorsal cirri and a few tentacular cirri lost; right parapodia of chaetigers 2 and 9 removed for observation (kept in vial); integument granulose; antennae digitate as long as interocular distance, or twice as long as wide; anterior eyes slightly larger than posterior ones; lateral cushions mostly smooth, entire, last three chaetigers with longitudinal ridges; acicular lobes single, blunt, basally swollen; neurochaetal blades bidentate, distal tooth larger, guards mostly eroded, approaching distal tooth].

New Caledonia. 3 specimens, MNHN-IA-PNT94 (formerly jar Musorstom 710), Lagoon Est, Sta. 710 (21°24.0’S, 166°02.5’E), 30 -31 m depth, 10.VIII.1986, B. Richer coll. [20-25 mm long, 3.0- 3.5 mm wide; macerated; integument smooth; body and anterior eyes unpigmented, acicular lobe single; neurochaetal blades bidentate, teeth tiny, subdistal tooth as large as distal one]. — 1 specimen, MNHN-IA-PNT94 (formerly jar Musorstom 713), Lagoon Est, Sta. 713 (22°22.6’S, 166°00.7’E), 34-35 m depth, 11.VIII.1986 [34 mm long, 5 mm wide; complete, distorted, laterally bent, with an anteroventral dissection; anterior eyes blackish, as long as wide, twice larger than posterior, round brownish eyes; integument smooth, with longitudinal furrows; acicular lobe single; most neurochaetal blades lost, bidentate, guard approaching distal tooth, most broken; dorsal cirrophore 2-3 times as long as wide; ventral cirri irregularly wrinkled].

Indonesia. 2 specimens, BMNH 1910.3.10.6/7, Goram Island, Gorong Archipelago, Maluku Islands, Stalker coll., no further data [complete, colorful, bent ventrally specimens; pigmentation pattern resembles Grube’s illustration for H. intertexta, including lateral darker spots; body 32-54 mm long, 4.5-5.5 mm wide; integument rugose, including lateral cushions, posterior ones with projected rounded tubercles along dorsal and lateral surfaces; right parapodium of chaetiger 7 removed for observation (kept in vial); acicular lobe single, with a swollen base; neurochaetal blades bidentate, subdistal tooth smaller, guards broken, remaining ones approaching subdistal tooth].

ETYMOLOGY. — This species is named after the late Dr R. Horst, from the Leiden Museum, a very productive taxonomist of polychaetes, oligochaetes, sipunculans and some other invertebrate and vertebrate groups, in recognition of his many publications of Indonesian and Siboga Expedition polychaetes. The name is a noun in genitive (ICZN 1999: art. 31.1.2).

DISTRIBUTION. — Southern Japan to Indonesia, Australia and New Caledonia, in mixed bottoms, 3-36 m water depth.

DIAGNOSIS. — Hesione with prostomium laterally curved; parapodia with dorsal cirri basally cylindrical, dorsal cirrophore twice as long as wide; larger acicula pale; acicular lobe single, digitate, basally swollen, lower tine missing; neurochaetal blades bidentate, 6-12 times as long as wide; teeth subequal; guards approaching subdistal tooth. DESCRIPTION

Holotype, RMNH 19913, complete, bent laterally, subcylindrical, tapered posteriorly; prostomium whithish, integument brownish, no pigmentation pattern (Fig. 21A) in ethanol; most tentacular and dorsal cirri broken; right parapodia of chaetigers 2, 7, 14 removed for observation (kept in vial). Body 20 mm long, 2 mm wide.

Prostomium as long as wide, anterior margin projected anteriorly, lateral margins slightly rounded, posterior margin exposed, deeply cleft along 1/3 prostomial surface, longitudinal depression indistinct (Fig. 21B). Antennae minute, digitate, 3-4 times as long as wide. Eyes colorless, size relationship between anterior and posterior eyes unknown.

Tentacular cirri broken. Lateral cushions barely projected, most entire but some divided into two or three sections.

Parapodia with chaetal lobes tapered, truncate; dorsal cirrophores about twice as long as wide (Fig. 21C); cirrostyle basally cylindrical, articulated, medially annulated, tips and size relationship with body width unknown. Ventral cirri smooth, barely corrugated, surpassing chaetal lobe.

Neuraciculae honey-colored, two per parapodium, thinner shorter, thicker reaching chaetal lobe margin. Acicular lobe single, digitate, swollen basally (Fig. 21C [inset]).

Neurochaetae about 30 per bundle, blades at a certain angle from handle, blades bidentate, 6-12 times as long as wide, teeth minute, similar-sized, usually directed distally, guard approaching subdistal tooth (Fig. 21D [insets]).

Posterior region tapered into a blunt cone (Fig. 21E); pygidium barely swollen, anus damaged, papillae indistinct.

Pharynx not everted in holotype. Oocytes not seen.

Pigmentation

There are no records of living specimens.

REMARKS

Hesione horsti n. sp. is unique in the genus because it has honey-colored neuraciculae, either both, or only the larger one, and its neurochaetae have guards approaching subdistal tooth, but blades are long with tiny teeth, and these blades which can be found along a few anterior chaetigers in other species, are present along all chaetigers, at least in the upper part of the chaetal bundle. The holotype was regarded as a juvenile of H. intertexta by Horst (1924), but despite their resemblance to the juveniles of other species, which might also have paler neuraciculae, especially along a few anterior chaetigers, larger pale neuraciculae are present along the body of the holotype of H. horsti n. sp., and its long neurochaetal blades are not restricted to anterior chaetigers.