Eunice siphoninsidiator Zhou, Zhang, Shen & Zhang, 2025

Eunice siphoninsidiator Zhou, Zhang, Shen & Zhang sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3

Type material.

Holotype: • RSIOPOLY 80001 , O-Hakucho Guyot , Northwest Pacific, 23.01 ° N, 148.58 ° E, 1135 m depth; Jiaolong dive JL 230, R/V Shenhaiyihao cruise DY 80-I; 27 June 2023; fixed in 100 % (v/v) ethanol GoogleMaps . Paratype: • two specimens. Paratype 1 #, RSIOPOLY 80002 , O-Hakucho Guyot , Northwest Pacific, 22.93 ° N, 148.56 ° E, 1175 m depth; Jiaolong dive JL 233, R/V Shenhaiyihao cruise DY 80-I; 30 June 2023; fixed in 100 % (v/v) ethanol GoogleMaps ; • Paratype 2 #, RSIOPOLY 86005 , Albo Guyot , Northwest Pacific, 17.0001 ° N, 154.2679 ° E, 1057 m depth, Jiaolong dive JL 311, R/V Shenhaiyihao cruise DY 86-II, 3 September 2024, fixed in 10 % (v/v) formalin, partial tissue fixed in 100 % (v / v) ethanol GoogleMaps .

Additional material.

Five specimens, incomplete. • RSIOPOLY 86001 and RSIOPOLY 86003 , Albo Guyot , Northwest Pacific, 16.9998 ° N, 154.7687 ° E, 1107 m depth, Jiaolong dive JL 311, R/V Shenhaiyihao cruise DY 86-II, 3 September 2024, anterior part fixed in 100 % (v/v) ethanol GoogleMaps ; • RSIOPOLY 86014 , DD Seamount , Northwest Pacific, 23.8150 ° N, 148.7926 ° E, 1055 m depth, Jiaolong dive JL 302, R/V Shenhaiyihao cruise DY 86-II, 20 August 2024, anterior part fixed in 100 % (v/v) ethanol GoogleMaps ; • RSIOPOLY 86015 , DD Seamount , Northwest Pacific, 23.8150 ° N, 148.7915 ° E, 1047 m depth, Jiaolong dive JL 302, R/V Shenhaiyihao cruise DY 86-II, 20 August 2024, anterior part fixed in 100 % (v/v) ethanol GoogleMaps ; • RSIOPOLY 86016 , Albo Guyot , Northwest Pacific, 17.0143 ° N, 154.3549 ° E, 1126 m depth, Jiaolong dive JL 312, R/V Shenhaiyihao cruise DY 86-II, 4 September 2024, anterior part fixed in 100 % (v/v) ethanol GoogleMaps .

Measurements

(before fixation). Holotype complete, with 95 chaetigers, total length 177 mm, first 10 chaetigers 11.5 mm in length, width at chaetiger 10 without parapodia 10 mm. Paratype 1 # complete, with 107 chaetigers, total length 140 mm, first 10 chaetigers 8.1 mm in length, width at chaetiger 10 without parapodia 6.1 mm. Paratype 2 # complete, with 103 chaetigers, total length 151 mm, first 10 chaetigers 11.2 mm in length, width at chaetiger 10 without parapodia 6.7 mm.

Description.

Live specimens iridescent brownish or slightly pinkish with lighter patches along the body. Preserved specimens pale white, slightly iridescent. Body long, dorsally convex, and ventrally flat (Fig. 2 C, D View Figure 2 ).

Prostomium narrower and shorter than first peristomial ring, bilobed anteriorly with round anterior ends and deep median sulcus (Fig. 2 E, F View Figure 2 ). Prostomial appendages in semicircle, with lateral antennae closer to palps than to median antennae (Fig. 2 E – H View Figure 2 ). Antennae 2 × longer than palps, reaching anterior end of chaetiger 5 when reversing; median antennae about 1.5 × as long as lateral antennae (Fig. 2 E, F View Figure 2 ). Ceratophores of antennae and palps short and ring-shaped, usually covered by prostomium; ceratostyles long, tapering, with indistinct articulations; palpstyles tapering digitiform distally with indistinct articulations (Fig. 2 E – G View Figure 2 ). Eyes dark, lateral to ceratophores of lateral antennae (Fig. 2 G View Figure 2 ).

Peristomium cylindrical, separation between first and second ring visible on both dorsal and ventral sides (Fig. 2 E, F View Figure 2 ); first ring more than 5 / 6 as long as of whole peristomium; peristomial cirri tapering, indistinctly articulated, reaching anterior end (middle in paratype) of first peristomial ring (Fig. 2 E, F View Figure 2 ).

Mandibles dark brown, with white wing-shaped calcareous cutting edges (Fig. 2 I View Figure 2 ). Maxillary apparatus brown to dark brown. Maxillae formula MxI 1 + 1, MxII 6 + 5, MxIII 8 + 0, MxIV 5 + 5, MxV 1 + 1, MxVI 1 + 1. All teeth with blunt ends. Mx-I about 3 × as long as carrier. MxV with a large square ridge; MxVI reduced to a plate with a minute tooth (Fig. 2 J, K View Figure 2 ).

Branchiae from chaetiger 9 to near posterior end (Fig. 3 A – C View Figure 3 ), pectinate, always shorter and slender than dorsal cirri (Fig. 3 A, B View Figure 3 ), with 1–2 short filaments on most anterior and most posterior branchial segments, increasing to 4–5 filaments on following parapodia and reaching a maximum of 7–8 at middle region (Fig. 3 D – F View Figure 3 ).

Dorsal cirri tapering, indistinctly articulated distally in anterior chaetigers, then smooth, slightly thicker on prebranchial segments and slender on posterior segments (Fig. 3 A – G View Figure 3 ). Ventral cirri 1 / 4–1 / 3 and 2–3 as long as dorsal cirri and chaetal lobes, respectively, gradually shortening from anterior to posterior regions. First four ventral cirri short, digitiform, strong; following ones with suboval basal inflation and a short tapering tip from chaetiger 5 through 37; subsequent ventral cirri digitiform (Fig. 3 D – G View Figure 3 ).

Chaetal lobs obliquely truncate, longer dorsally than ventrally, with aciculae emerging dorsal to midline. Prechaetal lobe low transverse fold. Postchaetal lobes round or obliquely truncate, inflated on all chaetigers. Limbate chaetae supracicular, tapering and slender (Fig. 3 H View Figure 3 ). Thin pectinate chaetae emerging from chaetiger 5 to last chaetiger, tapering, flat with 12–16 teeth; one marginal teeth longer than others (Fig. 3 I View Figure 3 ). Shafts of compound falcigers smooth, slender at basal part, expanded distally; blades bidentate, with proximal tooth triangular, similar to distal tooth in length, directed laterally; distal tooth slightly curved, slightly slenderer than proximal tooth (Fig. 3 J, K View Figure 3 ). Aciculae dark brown, straight or slightly bent, tapering with blunt or pointed tips, 1–3 in each parapodium (Fig. 3 E View Figure 3 ). Subacicular hook bidentate, dark brown, from chaetiger 27 to last segment, 1–2 per parapodium; proximal tooth triangular, directed laterally; distal tooth, smaller than proximal tooth, directed upwards (Fig. 3 L, M View Figure 3 ).

Pygidium with two pairs of smooth anal cirri, most ventral pair short and slender; dorsal pair much longer and thicker, extending to last 6 th chaetiger when folded anteriorly (Fig. 3 C View Figure 3 ).

Variation.

Relative length of peristomial cirri to first ring of peristomium close to 1: 1 in holotype, paratype 2 # and 4 other individuals, but close to 1: 2 in paratype 1 #. Holotype with bifurcated dorsal cirri in left parapodia of chaetigers 14 and 45 and in right parapodia of chaetiger 44, absent in paratype (Fig. 3 B, F View Figure 3 ). Starting of branchiae and subacicular hook ranging from chaetiger 8–11 and 27–32, respectively, in all examined specimens.

Etymology.

A combination of two Latin words: ‘ siphon - ’ meaning ‘ tube’ or ‘ pipe’ and ‘ insidiator ’ meaning ‘ ambusher’. This is a reference to the behavior of the species as ambush predator living within tubular structure of glass sponges. This name is to be treated as noun in apposition.

Distribution.

Found living in association with deep-sea glass sponges on seamounts in the northwest Pacific.

Remarks.

Eunice siphoninsidiator sp. nov. belongs to group B- 2 as proposed by Fauchald (1992) based on its dark bidentate subacicular hooks and high percentage of branchial chaetigers (> 65 %). It has indistinctly articulated prostomial appendages and anterior dorsal cirri, and reduced branchiae with only a few short branchial filaments (<8 and shorter than the notopodial dorsal cirri), thus most closely resembles Eunice norvegica ( Linnaeus, 1767) . However, E. siphoninsidiator sp. nov. has a ~ 1 / 1 relative length of palps compared to peristomium (1 / 2 in E. norvegica ), subacicular hooks starting from chaetiger 27–32 (42 / 44 in E. norvegica ) and pectinate chaetae asymmetric, with one marginal tooth much longer than others (symmetric, with two slightly longer marginal teeth in E. norvegica ). Moreover, they differ by 13 % in K 2 P genetic distance (Suppl. material 2).