Eusthenelais hibernica McIntosh, 1876

Barnich, Ruth & Haaren, Ton Van, 2021, Revision of Sthenelais Kinberg, 1856, Fimbriosthenelais Pettibone, 1971 and Eusthenelais McIntosh, 1876 (Polychaeta, Sigalionidae) in the Northeast Atlantic, European Journal of Taxonomy 740, pp. 138-171 : 162-165

Eusthenelais hibernica McIntosh, 1876 (emended)

Fig. 8

Eusthenelais hibernica McIntosh, 1876b: 407 , pl. 73, figs 4–5.

Sthenelais jeffreysi McIntosh, 1876b: 406 , pl. 72 fig. 18, pl. 73 figs 1–2 (synonymy according to Eliason 1962, confirmed herein).

Sthenelais heterochaeta McIntosh, 1897b: 176 , pl. 3 figs 6–10 (synonymy acc. to Eliason 1962, confirmed herein).

Eusthenelais hibernica – McIntosh 1900: 425, pl. 29 fig. 5, pl. 31 fig. 9, pl. 42 figs 9–10. — Gil 2011: 937. — Núñez et al. 2015: 233, fig. 93.

Sthenelais Jeffreysii – McIntosh 1900: 421, pl. 29 fig. 4, pl. 31 fig. 7, pl. 34 fig. 13, pl. 42 figs 5–8. — Gil 2011: 947.

Sthenelais jeffreysi – Eliason 1962: 224 fig. 5b–h.

Parasthenelais hibernica – Amoureux 1972: 68, fig. 1. — Barnich & Fiege 2003: 11.

Diagnosis

Dorsal cirri present on segment 3. Ventral body surface and parapodial stylodes smooth. Outer elytral margin with several filiform papillae, elytral surface smooth. Neurochaetae spinigers and falcigers.

Type material (examined)

Eusthenelais hibernica :

IRELAND • syntype; NE Atlantic, W coast of Ireland; depth 106 fathoms (194 m); “ Porcupine ” expedition leg.; EtOH preserved; BMNH 1921.5.1.620 .

PORTUGAL • syntype; off Cape Sagres; depth 45 fathoms (82 m); “Porcupine” expedition leg.; EtOH preserved; BMNH 1921.5.1.621 .

Sthenelais jeffreysi :

IRELAND • holotype; NE Atlantic, W coast of Ireland, station 9; 53°16′ N, 12°42′ W; depth 165 fathoms (302 m); 1869; “Porcupine” expedition leg.; EtOH preserved; BMNH 1921.5.1.616 .

The syntypes of Sthenelais heterochaeta (type locality: Norway, Osterfjorden, NE Atlantic) are probably lost.

Other material (examined)

UNITED KINGDOM • 1 spec.; NW Scotland , Geikie Slide and Hebridean Slope; stn C05 S41 A1; 58.38° N, 9.40° W; depth 650 m; 23 Jul. 2016; sandy mud; EtOH preserved; survey code JNCC/MSS 1016S GSH; TUM 65469 • 1 spec.; same locality as for preceding; stn C11 S15 A1; 58.45° N, 9.32° W; depth 868 m; 21 Jul. 2016; coarse sandy mud; EtOH preserved; ex TUM 65481; survey code JNCC/MSS 1016S GSH; NMS.Z. 2020.14.4 • 1 spec.; same locality as for preceding; stn D03 S83 A1; 58.29° N, 9.30° W; depth 438 m; 29 Jul. 2016; sandy mud; EtOH preserved; ex TUM 65499; survey code JNCC/MSS 1016S GSH; NMS.Z.2020.14.1 • 1 spec.; same locality as for preceding; stn D11 S61 A1; 58.40° N, 9.17° W; depth 496 m; 25 Jul. 2016; sandy mud; EtOH preserved; ex TUM 65515; survey code JNCC/MSS 1016S GSH; NMS.Z. 2020.14.3 • 1 spec.; same locality as for preceding; stn F04 S90 A1; 58.47° N, 8.78° W; depth 410 m; 29 Jul. 2016; sandy mud; EtOH preserved; ex TUM 65547; survey code JNCC/MSS 1016S GSH; NMS.Z. 2020.14.2 • 1 spec.; same locality as for preceding; stn F16 S75 A1; 58.59° N, 8.45° W; depth 450 m; 28 Jul. 2016; sandy mud; EtOH preserved; ex TUM 65571; survey code JNCC/MSS 1016S GSH; NMS.Z. 2020.14.5. ( Fig. 8 )

Description

PROSTOMIUM. Median antenna with long, smooth, tapering style; ceratophore with small auricles. Lateral antennae fused to inner side of tentaculophores, size and shape similar to dorsal tentacular cirri. Eyes indistinct ( Fig. 8A ).

TENTACULOPHORES. Dorsal tentacular cirri long, size and shape similar to median antenna. Ventral tentacular cirri short, not reaching half the length of the dorsal ones ( Fig. 8A ).

ELYTRA. With filiform papillae on outer lateral margin and smooth surface ( Fig. 8B ).

CIRRI. Dorsal cirri present on segment 3, size and shape similar to dorsal tentacular cirri. Ventral cirri without basal knob or long basal papillae ( Fig. 8C–D ).

PARAPODIA. Stylodes without papillae, slender, cirriform, some slightly inflated basally. Parapodia of anterior and middle body with few stylodes present along notopodial bract, on neuropodial acicular lobe and on upper and lower parts of large, bilobed posterior neuropodial bract. Margins of neuropodial anterodorsal and anteroventral bracts smooth. Without long dorsal papillae on notopodia ( Fig. 8C–D ).

CHAETAE. Notochaetae slender, spinous, tapering to simple capillary tip. Upper neurochaetae all slender compound spinigers. Middle neurochaetae slender compound spinigers and stout compound falcigers with short, 1–4 articled blade and bidentate tip. Lower neurochaetae slender compound falcigers with multi-articled blade and minutely bidentate tip ( Fig. 8E–G ).

SIZE. Specimen figured: NMS.Z. 2020.14.5 ( Fig. 8 ): anterior fragment, length 45 mm, width 5 mm for 98 segments. Syntypes of Eusthenelais hibernica: BMNH 1921.5.1.620, anterior fragment, length 11 mm, width 2.5 mm for about 28 segments; BMNH 1921.5.1.621, anterior and middle fragment, total length about 17 mm, width 3.5 mm for 31 segments (total). Holotype of Sthenelais jeffreysi: BMNH 1921.5.1.616, anterior fragment, length 18 mm, width 3 mm for about 39 segments.

Remarks

The description above is emended for the terminology used in describing the parapodial bracts and stylodes and the details regarding the shape and location of the neurochaetae. The recently collected specimens of

E. hibernica from the Geikie Slide (Northwest Scotland) were in rather good condition and proved very helpful in supplementing the diagnostic characters of the species.

Chambers(1985) noted that the type material of Eusthenelais hibernica is unidentifiable and,consequently, Read & Fauchald (2020) list Eusthenelais McIntosh, 1876 as a nomen dubium in WoRMS. However, especially the presence of both spinigers and bidentate falcigers as described by McIntosh (1876b) is sufficient to distinguish it from other sigalionid species. The other important generic character, i.e., the presence of dorsal cirri on segment 3, was not mentioned in the original description, but later described by McIntosh (1900) based on the same material (see respective remark related to generic diagnosis above). We examined the syntypes, which are in rather bad condition, but we can confirm the presence of a pair of dorsal cirri on segment 3 in both specimens.

In both publications (1876b, 1900) McIntosh described Eusthenelais hibernica and Sthenelais jeffreysi as different species. It is not clear why he did not realise that these are in fact synonymous, as for both species he described the two types of neurochaetae and, although he did not mention the dorsal cirri in the text for S. jeffreysi , he clearly figured them in his monograph of 1900 (pl. 29 fig. 4).

Eliason (1962) noted that not only Sthenelais jeffreysi , but also Sthenelais heterochaeta McIntosh, 1897 could be possible synonyms of Eusthenelais hibernica . For S. heterochaeta again the dorsal cirri are not mentioned, but the original description of the elytral and chaetal characters leaves no doubt that this is E. hibernica .

We checked the holotype of S. jeffreysi and found it to be unidentifiable; moreover, the type material of S. heterochaeta seems to be lost. But, as explained above, the respective original descriptions are sufficient and we confirm Eliason’s view that both S. jeffreysi and S. heterochaeta are synonyms of E. hibernica .

Compared to the other species described herein, Eusthenelais hibernica presents a number of remarkable characters: The presence of a pair of dorsal cirri on segment 3 is the main differentiating character (absent in all other species). The auricles are smaller and much less obvious. The lateral antennae are of similar length to the dorsal tentacular cirri (versus distinctly shorter). The neuropodial posterior bract is large and obvious, similar to the one found in S. limicola (versus smaller and much less obvious in S. boa , or the Fimbriosthenelais species).

Distribution and habitat

So far only known from the NE Atlantic: recorded from off Norway, along the western coasts of the British Isles and Ireland, down to Southwest Portugal. Occurring on muddy and sandy substrates from 70 to 870 m depth (see above).

Figures

Fig. 8. Eusthenelais hibernica McIntosh, 1876. TUM 65571. A. Anterior end, left palp not figured, bent downwards. B. Left elytron of segment 17. C. Left parapodium of segment 19, anterior view. D. Same, posterior view. E–G. Neurochaetae of same, all distal part. E. Upper compound spiniger. F. Middle stout compound falciger. G. Lower slender compound falciger. Scale bars: A=2 mm; B–D =1 mm; E–G= 100 µm.