Hesione pacifica McIntosh, 1885

Salazar-Vallejo, Sergio I., 2018, Revision of Hesione Savigny in Lamarck, 1818 (Annelida, Errantia, Hesionidae), Zoosystema 40 (12), pp. 227-325 : 275-278

Hesione pacifica McIntosh, 1885 reinstated ( Figs 30-32 )

Hesione pacifica McIntosh, 1885: 184 , 185, pl. 29, fig. 2, pl. 32, fig. 14.

Hesione intertexta – Monro 1926: 311, 312 (partim, non Grube, 1878).

Hesione splendida – Augener 1913 a: 187; 1922: 21, figs 4, 4a. — Hartman 1966: 191 (non Savigny in Lamarck, 1818).

TYPE MATERIAL. — Tonga. Holotype, BMNH 85.12 .1.136, RV Challenger Expedition, Sta. 172 (20°58’S, 175°09’W), 200 km N off Tonga Island , 32 m depth, coral mud, 22.VII.1874.

ADDITIONAL MATERIAL. — French Polynesia. 1 specimen, USNM 19378 , RV Albatross, Sta. unnumb., Society Islands , Bora Bora, between shore and fringing reef, 17.XI.1899 [21 mm long, 3.5 mm wide; body incurved; most cirri lost, all chaetae broken; pharynx exposed, short, margin smooth; prostomial anterior margin truncate, with a shallow furrow; lateral margins expanded posteriorly; posterior margin with a short longitudinal furrow; antennae tapered, 2/3 as long as prostomium; dorsal cirri basally multiarticulated; acicular lobes double, of similar size; posterior region tapered into a blunt cone; anus with thick anal cirri] .

Northern Mariana Islands. 1 specimen, USNM 26069 , Lagoon N of Matuis Beach , NW Saipan Island, in dead Lithophyllum, base of brown Acropora , 12.XII.1948, P. E. Cloud Burke coll. [26 mm long, 4 mm wide; body incurved; slightly dehydrated; most cirri retained on body; many chaetal blades lost; prostomium directed ventrally, antennae tapered; eyes unpigmented; dorsal cirri multiarticulated; acicular lobe double, upper tine digitate, twice as long as lower one, blunt triangular; neurochaetal blades short, bidentate, guard approaching subdistal tooth, rarely surpassing it; posterior end tapered into a blunt cone; anus terminal, no anal papillae visible]. South China Sea. 1 specimen, BMNH 1926.4 .30.136, RV Alert Expedition, Macclesfield Bank, no further data [21 mm long, 2 mm wide; body bent laterally, integument rugose along a few anterior chaetigers, smooth in others; eyes barely pigmented; antennae tapered, 3-4 times as long as wide; anterior eyes twice larger than posterior ones; pharynx almost fully exposed, dorsal papilla covered by prostomium, slightly as long as wide, blunt; acicular lobe double, tines of similar length and width; all chaetae broken] .

Australia. 1 specimen, ZMH-P 7925, Sharks Bay, SW Australien Expedition 1905, no further data [24 mm long, 3 mm wide; strongly contracted, integument smooth, prostomium invaginated; colorless, acicular lobes single; neurochaetal blades bidentate, guard approaching distal tooth] . — 1 specimen, ZMH-P 9338, Cape Jaubert, NW Australia, E. Mjöberg coll. [30 mm long, 4 mm wide; colorless, partially dehydrated; integument smooth; antennae digitate, twice as long as wide; eyes brownish, anterior ones as long as wide, twice larger than posterior ones, interocular distance barely visible, eyes almost fused laterally; aciculae blackish, thin, tapered; acicular lobe single, basally swollen, blunt; neurochaetal blades bidentate, subdistal tooth smaller, teeth and guards eroded].

DISTRIBUTION. — This subtidal species is rarely found in sediments, up to 32 m water depth, from the Northern Mariana Islands to the French Polynesia and New Caledonia. The record for Hawaii by Treadwell (1906: 1149) rather matches H. genetta by sharing a dark brown transverse band on chaetiger 2 (see above).

DIAGNOSIS. — Hesione with prostomium curved laterally; parapodia with dorsal cirri basally cylindrical, dorsal cirrophore twice as long as wide; larger acicula blackish; acicular lobe double, tines digitate, upper one twice longer than lower one; neurochaetal blades bidentate, 2-3 times as long as wide; subdistal tooth as large as distal one, with guards approaching subdistal tooth.

DESCRIPTION

Holotype, BMNH 85.12 .1.136, complete, tapered posteriorly; integument smooth, brownish, some small middorsal dots in most segments ( Fig. 30A ) in ethanol; a ventral dissection running throughout first 14 chaetigers; right parapodium of chaetiger 7 and left parapodium of chaetiger 6 previously removed, right parapodium of chaetiger 15 removed for observation (kept in vial). Body straight , bent dorsally, 23 mm long, 3 mm wide.

Prostomium as long as wide, anterior margin projected anteriorly, lateral margins rounded, widest behind posterior eyes, posterior margin with a shallow notch, 1/5 as long as prostomium ( Fig. 30B ). Antennae digitate, longer than interocular distance, 4-5 times as long as wide. Eyes brownish, anterior ones slightly larger and farther apart than posterior ones.

Tentacular cirri thin, tips broken, longest ones reaching chaetiger 5. Lateral cushions low, surface smooth, divided into 2-3 (rarely 4) sections.

Parapodia with chaetal lobes eroded, most remaining ones invaginated; dorsal cirri most lost, with cirrophores twice as long as wide, cirrostyle basally cylindrical, smooth, medially and distally articulated, smaller than body width ( Fig. 30C ); ventral cirri regularly contracted, surpassing chaetal lobes.

Neuraciculae blackish, tapered. Acicular lobe double, short, tines blunt of similar size ( Fig. 30C, D ).

Neurochaetae about 20 per bundle, most trimmed, probably during ventral dissection, some with neurochaetal blades fragments, or blades lost ( Fig. 30C [inset]).

Posterior region tapered into a blunt cone ( Fig. 30D ); pygidium rugose, anus projected, dorsal margin and anal papillae eroded ( Fig. 30E ).

Pharynx not exposed. Oocytes about 100 µm in diameter.

REMARKS

Hesione pacifica McIntosh, 1885 , reinstated, was described with a single specimen (holotype). It was in good condition, without pigmentation pattern, but all neurochaetal blades were lost, probably as an indirect consequence of his dissection to observe the pharynx. McIntosh made two illustrations for the species (reproduced herein as Figure 31 ), one was a dorsal view of the whole specimen, showing all tentacular and dorsal cirri ( Fig. 31A ), probably before dissection, and the other was an anterior parapodium ( Fig. 31C ). The original prostomium was enlarged because it was too small in the original ( Fig. 31B ); the prostomial posterior margin has a shallow furrow and the antennae were illustrated as long, tapered filaments, 5 times as long as wide and longer than the distance between lateral eyes, but these features can only be noticed by using a hand lens over the original plates, or by observing it with a stereomicroscope. Further, the parapodium was illustrated but no acicular lobes were indicated, although the details for cirri are adequate. Once the relative size of antennae is observed, his remarks are easier to understand. He indicated that H. pacifica approaches H. intertexta but that they differ by the size of antennae, being longer in the former and shorter in the latter, and in their neurochaetal blades, because the subdistal tooth is larger in H. pacifica than in H. intertexta .

As indicated in the key below, the presence of subdistal teeth as wide as distal ones, groups H. pacifica with three other colorful species: H. genetta Grube, 1864 restricted, H. mooreae n. sp., and H. paulayi n. sp. Because the pigmentation pattern is long lasting in the latter three species (up to 100 years), and no pigmentation has been reported in H. pacifica , this is the main difference to sort them out. McIntosh and Chamberlin, studied their specimens 10-20 years after they were collected, and the latter also found H. genetta within the RV Albatross material.

Further, one specimen from the Mariana Islands (USNM 26069) was collected by the end of 1948, and Olga Hartman saw it 5 years after sampling, while preparing her paper on that archipelago ( Hartman 1954); no pigmentation was evident then, and none is visible now ( Fig. 32A ), but this would be the shortest time span between collection and identification, such that its pigmentation, if any present, must fade rather soon in comparison to the long-lasting pigmentation in specimens of both H. genetta and H. paulayi n. sp.

After the study of the best preserved specimen (USNM 26069, 26 mm long), some additional observations include: 1) antennae can appear shorter and even biarticulate if they are directed ventrally ( Fig. 32B ); 2) dorsal cirri can be longer than body width including parapodia, and that ventral cirri often projects beyond neurochaetal tips ( Fig. 32C ); 3) acicular lobes are double with the upper tines twice longer than lower ones ( Fig. 32C [inset]); and 4) there are about 20 neurochaetae per bundle, blades are 2-3 times as long as wide, bidentate with subdistal tooth slightly smaller than distal one, with guards approaching subdistal tooth ( Fig. 32D [inset]). Neurochaetal blade size was in a smaller range in H. pacifica (2-3 times as long as wide) than in H. genetta or H. paulayi n. sp. (3-5 times as long as wide).

Figures

FIG. 30. — Hesione pacifica McIntosh, 1885, holotype, BMNH 85.12.1.136: A, anterior region, dorsal view; B, prostomium, dorsal view (arrows point to antennae); C, chaetiger 15, right parapodium, anterior view (inset: neurochaetal remains); D, posterior region, dorsal view; E, same, close-up of pygidium. Scale bars: A, 1 mm; B, 0.2 mm; C, E, 0.3 mm; D, 0.9 mm.

FIG. 31. — Hesione pacifica McIntosh, 1885: A, dorsal view; B, head, dorsal view; C, parapodium from a midbody segment (modif. after McIntosh 1885; original without scale bars).

FIG. 32. — Hesione pacifica McIntosh, 1885, non-type specimen, USNM 26069: A, anterior region, dorsal view; B, prostomium, dorsal view, antennae directed ventrally; C, chaetiger 9, left parapodium, anterior view (inset: acicular lobe); D, same, neurochaetae (inset: tips of three blades); E, posterior region, dorsal view. Scale bars: A, 1.1 mm; B, 0.4 mm; C, 0.7 mm; D, 150 µm; E, 2.9 mm.