Ehlersileanira andamanensis, Aungtonya & Eibye-Jacobsen, 2016

Aungtonya, Charatsee & Eibye-Jacobsen, Danny, 2016, A New Species of the Genus Ehlersileanira (Polychaeta: Sigalionidae) from the Andaman Sea, Thailand, Species Diversity 21, pp. 111-116 : 114-115

Ehlersileanira andamanensis n. sp.

( Figs 1A–F , 2A–J ; Table 1)

Ehlersileanira incisa (not of Grube, 1877)— Aungtonya 2002: 226, fig. 13.

Ehlersileanira sp. — Aungtonya 2003: fig. 1a–b.

Holotype. PMBC 20305 , posteriorly incomplete, 39 segments, length 17 mm, width 3.25 mm including parapodia (about 3.5 mm wide including chaetae), BIOSHELF st. L-2/AT, 6°45′N, 99°04′E, 59–63 m, soft mud, 28 February 2000.

Paratype. PMBC 20304 , posteriorly incomplete, 53 segments, length 23 mm, width 2.75 mm including parapodia (about 3.5 mm wide including chaetae), BIOSHELF st . K-2/ OS, 7°00′N, 99°00′E, 60 m, soft mud, 6 May 1996 .

Other material examined. PMBC 15814 , 1 (dried), BIOSHELFst . L-2/AT, 6°45′N, 99°04′E, 59–63 m, soft mud, 28 Feb 2000; PMBC 19633 , 1 spec . on SEM stub, st. L-2/AT, 6°45′N, 99°04′E, 59–63 m, soft mud, 28 Feb 2000.

Description. All specimens posteriorly incomplete, PMBC 20304 being the largest.

Prostomium oval, wider than long, dorsally fused with tentacular parapodia. Parapodia of segments 1–3 directed anteriorly ( Figs 1A, E , 2A ). Three small antennae present; ceratophore of median antenna located on anterior margin of prostomium, with pair of prominent lateral auricles, and ctenidia seen beneath auricles ( Fig. 1B–C ); style of median antenna short, with two articles ( Fig. 1B ); lateral antennae both with similar style, ceratophore fused with dorsal side of tentacular parapodia. Eyes and nuchal organs indistinct. Dorsal side of tentacular parapodia with 1–2 stylodes on each side between base of dorsal tentacular cirrus and lateral antenna ( Fig. 1B ). Upper lip with facial tubercle. Palps extending to about segment 18–24, with inner and outer palpal sheaths ( Fig. 1E ). Segment 2 with ventral buccal cirri ( Fig. 1E ). Segment 3 without dorsal cirri but dorsal tubercles present ( Fig. 1D ). Branchiae begining at about segment 15 or 17; ctenidial pads between notopodia and elytrophores begining at about same place. Ventral cirri short, tapered, with small outer basal knob. Beginning at about segment 25–27 ( Fig. 2I–J ), tubular segmental papilla near base of ventral cirrus. Elytral surface smooth; outer lateral margin lacking papillae ( Figs 1A , 2H ).

Notopodia with well developed posterior upper lobe and anterior lower lobe, anterior upper lobe with circlets of stylodes, and with a large stylode near tip of acicular lobe. Notochaetae simple, coarsely to finely spinous capillaries. Neuropodia furnished with long, large stylodes, with short posterior upper and lower lobes covering bases of chaetae, distinct in posterior view, acicular lobe in the middle distinct in anterior view, anterior upper and lower lobes indistinct ( Figs 1F , 2B–D, I–J ). Neurochaetae compound spinigers with canaliculate blades; 1–2 simple spinous capillaries in an upper position may be present ( Fig. 2E–G ).

Etymology. This species is named for the Andaman Sea.

Remarks. The main features of these specimens resem- ble those of Ehlersileanira incisa , as described and figured by Pettibone (1970b) based on specimens up to 12 mm wide, including chaetae. The arrangement of neurochaetae in the present specimens is also similar to that in E. incisa ( Pettibone 1970b: fig. 11c).

Pettibone (1970b) stated that in E. incisa the ceratophore of the median antenna has either lateral auricles or ctenidia and that the worms lack dorsal tubercles on segment 3 ( Table 1). However, an auricle is an ear-shaped lobe ( Fauchald 1977) whereas a ctenidium is a comb-like structure ( Lawrence 1989). The appendages on the ceratophore of the median antenna in E. incisa are lateral auricles, not ctenidia ( Pettibone 1970b: fig. 10a, c; Aungtonya 2005; therefore, the present specimens are recorded here as a new species.

In the present specimens the branchiae distinct from E. incisa begin at about segment 15 or 17, whereas in E. incisa they are present from about segment 30 posteriorly, with smaller rudimentary ones more anteriorly according to Pettibone (1970b); this difference also applies to the occurrence of ctenidial pads between the notopodia and elytrophores, beginning in the same region as the branchiae. Furthermore, the specimens studied clearly demonstrate the presence of both auricles and paired ctenidia on the ceratophore of the median antenna as well as dorsal tubercles on segment 3.

The validity of the diagnostic features of the new species is supported by examination of speciemens of E. incisa from the west coast of Africa that are stored in the Natural History Museum in London , U .K. One lot ( BMNH 1930.10 .8.1172 from Cape Lopez ) consists of one specimen and two large fragments (about 4 mm wide including chaetae). The ceratophore of the median antenna possesses only the right lateral auricles and there are no dorsal tubercles on segment 3. Branchiae begin at segment 9 and tubular segmental papillae begin at segment 11. On the only specimen in the other lot ( BMNH 1930.10 .8.1175 from St. Paul de Loanda ), which is about 2.3 mm wide including chaetae, the ceratophore of the median antenna possesses only the left and lateral auricles and lacks dorsal tubercles on segment 3 . Branchiae begin at segment 9 and tubular segmental papillae begin at segment 9.

Figures

Fig. 1. Ehlersileanira andamanensis n. sp. A–B, anterior end, dorsal view, with dorsal tentacular cirri and second parapodium on left removed; C, close-up of ceratophore of median antenna, showing auricles and one ctenidium; D, anterior end, dorsal view, (right elytron of segment 2 removed, and specimen was recoated); E, anterior end, ventral view; F, neuropodium of segment 3, anterior view. SEM micrographs all of PMBC 19633. Scales=1.0mm (A), 200µm (D–E), 100µm (B, F), and 10µm (C). Abbreviations: acl=acicular lobe, au=auricle, buc=buccal cirrus, ct=ctenidium, dtu=dorsal tubercle, ipas=inner palpal sheath, lan=lateral antenna, man=median antenna, opas=outer palpal sheath, pa=palp, st=stylode, vc=ventral cirrus.

Fig. 2. Ehlersileanira andamanensis n. sp.: A, anterior end, dorsal view, auricles are relatively big but the specimen was drawn at the attitude in order to show the lateral antenna on left, second article of median and left lateral antennae are folding, while that of lateral antennae on right is missing, dorsal tubercles on segment 3 are noticed; B, parapodium of segment 17, anterior view; C, posterior view of B; D, diagrammatic end-view of neuropodium from B, chaetae and stylodes indicated, anterior to left; E, upper neurochaeta (simple, spinous capillary) from B; F–G, neurochaetae (compound spinigers) from B; H, left elytron from segment 17, position of scar indicated; I, parapodium of segment 34, posterior view; J, anterior view of same, PMBC 20304 (A–H) and PMBC 15814 (I–J). Scales=1.0mm (H), 0.5mm (A–C, I–J), and 200µm (E–G). Abbreviation: sp=segmental papilla.