Hesione eugeniae Kinberg, 1866

Salazar-Vallejo, Sergio I., 2018, Revision of Hesione Savigny in Lamarck, 1818 (Annelida, Errantia, Hesionidae), Zoosystema 40 (12), pp. 227-325 : 245-249

Hesione eugeniae Kinberg, 1866

( Figs 10-12 )

Hesione eugeniae Kinberg, 1866: 244 ; 1910: 57, pl. 23, fig. 8. — Monro 1926: 312. — Hartman 1949: 46, 47, pl. 7, figs 8, 9.

Hesione intertexta – Horst 1924: 192, 193 (partim: Siboga Sta. 164, 274, non Grube, 1878).

Hesione cf. picta – Ngamniyom et al. 2014: 723, 724, figs 2, 3. — Lee & Ong 2015: 201, 202, figs 1, 2.

TYPE MATERIAL. — Indonesia. Holotype, RV Eugeniae, unnumb. Station, Bangka Strait (02°32’33”S, 105°44’36”E), between Java and Bangka Island , no further data (not seen; broken in two pieces and dried out from 1913 fide Hartman 1949: 46).

ADDITIONAL MATERIAL. — Indonesia. 1 specimen, RMNH V429 , Nassi Besaan, Malacca Strait (04°N, 100°E), mud, 9 m depth, 23.VI.1908, P. N. van Kampen coll. [22 mm long, 4 mm wide; body fusiform, turgid, many cirri lost; prostomium fully exposed; anterior eyes about twice as large as posterior ones; antennae digitate, tips slightly eroded, 4 times as long as wide; acicular lobes without basal knob; most chaetal blades broken; gonads partially exposed by body wall fracture, with oocytes 100 µm in diameter] . — 1 specimen, RMNH V430 , Malacca Strait, Gierg Exped., unnumb. Sta. (00°40’N, 99°10’E), 23.VI.1908, P.N. van Kampen coll. [30 mm long, 3 mm wide; macerated, colorless; body subcylindrical, tapered posteriorly; acicular lobe tapered, 5-7 times longer than round basal tine, visible only in a few chaetigers; gonad fragments removed through previous dissection, oocytes 100 µm in diameter] . — 1 specimen, RMNH V431.3 , Irian Jaya, RV Siboga Exped. Stat. 164 (01°42.5’S, 130°47.5’E), 32 m depth, dredge, sand, stones, shells, 20.VIII.1899 [28 mm long, 3 mm wide; complete, resembling pigmentation pattern as in RMNH V431.6 , but body thicker, right parapodium of chaetiger 7 removed for observation (kept in vial); acicular lobe with upper tine about 6 times longer than lower knob; neurochaetal blades bidentate, subdistal tooth smaller, guard markedly projected beyond distal tooth] . — 1 specimen, RMNH V431.6 , Irian Jaya, RV Siboga Exped. Stat. 274 (05°28.2’S, 134°53.9’E), 57 m depth, dredge, sand, shells, stones, 26.XII.1899 [longest specimen, used for Redescription] .

Gulf of Thailand. 1 specimen, ECOSUR 2909 , Songkla, about 30 km offshore, 23 m depth, muddy sand, III.2011 [23 mm long, 2.5 mm wide; body slightly curved laterally, without pigmentation pharynx partially everted; antennae digitate, shorter than interocular distance; eyes brownish, anterior ones almost twice as large as posterior ones; acicular lobes long, tapered, ¼-1/3 as long as chaetae; dorsal cirrostyle basally annulose, cylindrical, longer than body width but not including parapodia; ventral cirri irregularly wrinkled, markedly longer than chaetal lobe; neurochaetae with blades bidentate, subdistal tooth minute, guard projected beyond distal tooth; anal cone projected, with 6 low anal papillae] .

Torres Strait, Holothuria Bank . 1 specimen, BMNH 1926.4.30.106, Torres Strait [see Monro 1926] [complete, bent laterally, some parapodia previously removed; colorless, 38 mm long, 4.5 mm wide; acicular lobe single, chaetal blades long, with guard projected beyond distal tooth; pharynx exposed, dorsal papilla slightly as long as wide].

DISTRIBUTION. — Gulf of Thailand, Java Sea to Torres Strait, in 3-57 m depth, in sandy or mixed bottoms.

A B

DIAGNOSIS. — Hesione with prostomium laterally curved; parapodia with dorsal cirri basally cylindrical, dorsal cirrophore twice as long as wide; larger acicula blackish; acicular lobe single, digitate; neurochaetal blades bidentate, 4-10 times as long as wide; subdistal tooth smaller than distal one, with guards surpassing distal tooth.

REDESCRIPTION

Specimen RMNH V431.6, complete, with brownish diffuse dorsal pigmentation over chaetigers 1-4 ( Fig. 10A ), and other barely pigmented areas in medial and posterior chaetigers in ethanol; most tentacular and dorsal cirri without tips; right parapodium of chaetiger 8 removed for observation (kept in vial). Body straight, subcylindrical, tapered posteriorly, 29 mm long, 2.5 mm wide.

Prostomium semicircular, as long as wide, anterior margin projected anteriorly, lateral margins rounded, progressively expanded, posterior margin covered by tentacular segment anterior margin; without longitudinal depression. Antennae as long as anterior eye diameter, digitate, blunt, 4-5 times as long as wide ( Fig. 10B ). Eyes barely pigmented, anterior ones about twice as large as posterior ones.

Tentacular cirri long, irregularly twisted, longest one reaching chaetiger 5. Lateral cushions very low, most divided into three sections.

Parapodia with chaetal lobes as long as wide, tapered, truncate; dorsal cirri with cirrophores 1-2 times as long as wide; cirrostyle cylindrical basally, smooth, annulated medially, distally articulated ( Fig. 10C ), sometimes macerated ( Fig. 10D ). Ventral cirri smooth, tips eroded, if complete surpassing chaetal lobe.

Neuraciculae blackish, two, one thinner, the other thicker, tapered, tips colorless. Acicular lobe single, tapered, sometimes with a small, rounded to lobate lower tine, 1/5 as long as upper tine ( Fig. 10C, D [insets]).

Neurochaetae about 40 per bundle, blades bidentate, 4-10 times as long as wide, at a certain angle from the handle, decreasing in size ventrally, each with tiny subdistal tooth, guard, if entire, markedly projected beyond distal tooth ( Fig. 10E ).

Posterior region tapered into a blunt cone; pygidium shiny, slightly granulate ( Fig. 10F ), anus with seven rounded papillae.

Pharynx not exposed. Oocytes not seen (another specimen, RMNH 430 with oocytes about 100 µm in diameter).

Pigmentation

Body with transverse brown wide bands ( Fig. 11A ). Each band with darker, blackish lines along anterior and posterior margins, more irregular on anterior margins ( Fig. 11B ). Bands extended along body, dorsally interrupted segmentally along chaetal lobes by a narrow pale band (1/3 as long as dark band), barely visible in chaetiger 1, with unpigmented anterior and posterior rounded areas in chaetiger 16. Each band with homogeneous pigmentation, rarely with thin, irregular transverse paler lines, especially visible along chaetigers 1-2. Prostomium with a pale orange central along its anterior half, posterior half pale. Tentacular cirri, dorsal cirri, and chaetal lobes whitish. Eyes reddish brown, of similar size. Dark large pink rounded spots ventrally, at the level of chaetal lobes ( Lee & Ong 2015). Pygidium with a dark thin band, and paler areas before it, and in anal region.

REMARKS

Hesione eugeniae Kinberg, 1866 was briefly described ( Kinberg 1866: 244) and later illustrated ( Kinberg 1910: pl. 23, figs 8B, F, G) and the figures are herein reproduced ( Fig. 12 ). Antennae were shown as long as interocular distance ( Fig. 12A ); the parapodium does not show an acicular lobe ( Fig. 12B ), probably because it is rather thin and difficult to be noticed when a single parapodium is seen in posterior view, ventral cirri extend beyond chaetal lobes but not beyond chaetal tips. The most distinctive feature, because it has been regarded as unique, is the long guard present in neurochaetal blades, which was shown as clearly projected beyond distal teeth ( Fig. 12C ). Further, Monro (1926: 312) indicated that in one of his specimens from Torres Strait, there was a single acicular lobe. Hartman (1948: 46, 47) corroborated this by referring that the guard “[…] extends well beyond the terminal fang”, and that the subapical tooth was “small and inconspicuous”. However, her figures failed to show the very long guard, but they depict a remarkable difference in neurochaetal blade length/width relationship, being 4: 1 for the short blade and 11: 1 for the long one. Because the corresponding parapodia were not detailed, these ranges would imply that probably Hartman took chaetae from the first few chaetigers and from another median chaetiger, because their proportion decreases along the body, but in our specimens this range is confirmed in the same chaetal bundle.

In his revision of the Siboga Expedition material, Horst (1924: 192, 193) noted three specimens with a distinct pigmentation, inserted a question mark in the labels but included them under H. intertexta by indicating: “Three specimens only, from Stat. 164 and 274 and from Malacca-Strait did not show any longitudinal stripes, only a pale band, bordered by a dark line, across the dorsal side of the segments, between each pair of parapodia, as in Hes. vittata (sic) Ehl.” (synonym of H. picta Müller, 1858 , mihi). Horst (1924) gave no indications for chaetal features.

Hessle (1925: 14) recorded a small specimen from Sagami, central Japan, as H. splendida with transverse white bands. If the brownish bands were well-defined or not was not specified, and this specimen might belong to H. eugeniae , or rather be a dark form of H. reticulata von Marenzeller, 1879 , redescribed elsewhere ( Jimi et al. 2017), as that species was described from the same area; solving this requires a study of Hessle’s specimen to confirm its chaetal pattern.

The color photographs by Ngamniyom et al. (2014) and Lee & Ong (2015) reveal that the pigmentation pattern includes dorsal, segmental, wide, irregularly defined brownish bands, each with a darker thin line on their anterior and posterior margins, leaving the prostomium barely pigmented and the pygidium pale, although the latter has a darker bordering ring. Further, Lee & Ong (2015) also illustrated a midventral dark pink round spot per segment, including prostomium and pygidium, although in the former the spot is divided leaving a pale midventral area, and the pygidium has a smaller spot than those present in preceding segments. Chaetal features were not precised. Ngamniyom et al. (2014: fig. 2f) referred to unidentate falcigers although their figure could explain they confused the long guard as a single tooth, whereas Lee & Ong (2015: 201) correctly referred them as bidentate with guard (they called it accessory spine) “reaching beyond the primary (distal) tooth” but failed to illustrate them.

Hesione eugeniae Kinberg, 1866 is distinguished by having wide, transverse, solid, irregular bands along the dorsal pale surface, including the pygidium, long antennae, parapodia with acicular lobes single, and bidentate blades with tiny subdistal tooth, and guards surpassing the distal tooth. It differs from other species having transverse bands such as H. genetta Grube, 1864 , or H. picta Müller, 1858 because of the relative size of antennae, parapodial features and pigmentation patterns. In H. genetta antennae are large (as long as interocular distance), acicular lobes are double, and in neurochaetal blades, subdistal teeth are as large as distal ones, with guards approaching subdistal teeth; for pigmentation, the first band is wider than the following ones, and there are usually round spots between bands, but intermediate spots are missing in both H. picta and H. eugeniae . The banding pattern of the two latter species is similar because they have wide dark bands throughout the body, but their pigmentation intensity is different. In H. eugeniae bands are solid and the marginal lines are darker, whereas in H. picta there are no darker marginal lines, and the band itself includes several transverse thin pale lines. Further, unlike H. genetta , brownish bands in both H. picta and H. eugeniae fade off soon after specimens are preserved in ethanol, although the pygidium might retain the pigmentation for a longer time. For example, when one of the New Caledonia specimens was sorted out 16 years ago (Salazar-Vallejo 1999: 22), it had a blackish pygidium, and when it was re-examined (June, 2016) it has become reddish.

On the other hand, H. eugeniae resembles H. osbornae n. sp. because their neurochaetal blades have guards surpassing distal teeth. There are two main differences between these species. In H. eugeniae acicular lobes are digitate, and neurochaetal blades are 4-10 times as long as wide, whereas in H. osbornae n. sp. acicular lobes are tapered, and neurochaetal blades are about 15 times as long as wide.

Figures

FIG. 10. — Hesione eugeniae Kinberg, 1866, non-type specimen, RMNH V431.6: A, anterior region, dorsal view; B, prostomium, dorsal view, illuminated from posterior region to enhance visibility of antennae (indicated by arrows);C, chaetiger 8, right parapodium, anterior view (inset: acicular lobe); D, another specimen (RMNH V431.3), chaetiger 7, right parapodium, anterior view (inset: acicular lobe); E, another specimen, RMNH V430, chaetiger 8, blades of upper, medial and lower neurochaetae (inset: tip of one of them); F, another specimen, RMNH V431.6, posterior region, dorsal view. Scale bars: A, 1.2 mm; B, 0.2 mm; C, 0.5 mm; D, 0.03 mm; E, 40 µm; F, 1 mm.

FIG. 11. — Hesione eugeniae Kinberg, 1866, living specimen, Singapore: A, dorsal view; B, anterior region, dorsal view.Scale bars: A, 2.5 mm; B, 1 mm (Photos: Rene Ong).

FIG. 12. — Hesione eugeniae Kinberg,1866:A, anterior end,dorsal view;B, parapodium from a middle-body segment; C, same,close-up of neurochaetal tip; guard tip surpassing distal tooth (modif. after Kinberg 1910; original without scale bars).