Acanthicolepis zibrowii, Barnich, Ruth & Fiege, Dieter, 2010

Barnich, Ruth & Fiege, Dieter, 2010, On the distinction of Harmothoe globifera (G. O. Sars, 1873) and some other easily confused polynoids in the NE Atlantic, with the description of a new species of Acanthicolepis Norman in McIntosh, 1900 (Polychaeta, Polynoidae), Zootaxa 2525, pp. 1-18 : 13-15

Acanthicolepis zibrowii n. sp.

( Fig. 5 A–I)

Leucia nivea: Barnich & Fiege (2009) : 8, 11; Fiege & Barnich (2009): 159 [not Leucia nivea ( M. Sars, 1863) ].

Type material. Acanthicolepis zibrowii n. sp.: 2 syntypes (1 cs with 18 pairs of elytra, 1 cs with 15 pairs (juvenile); elytra all free in vial), SMF 17300, VITAL Expedition, "Atalante" St. 12, ROV Victor dive 189, NE Atlantic, Bay of Biscay, Saint-Nazaire Terrace, 46°15'N 4°43'W, 28 August 2002, 1250 m, on Madrepora oculata , grab sampler, ded. H. Zibrowius.

Diagnosis. Elytral margin with scattered papillae, long at outer lateral margin, shorter at posterior margin; microtubercles rounded, bifid, or branched multifid, becoming gradually larger towards lateral and posterior margin; macrotubercles in a row near posterior margin, cylindrical to club-shaped, distally nodular to spiny.

Description (based on large syntype and on anterior elytron free in vial, SMF 17300). Body with 41 segments. At anterior end ( Fig. 5 A), prostomium bilobed, with distinct cephalic peaks; ceratophore of median antenna in anterior notch, lateral antennae inserted ventrally, style papillate, tapering (styles of median and left lateral antenna missing); anterior pair of eyes situated dorsolaterally at widest part of prostomium, posterior pair dorsally near hind margin of prostomium; palps papillate, tapering.

Tentaculophores inserted laterally to prostomium, each with four notochaetae and a dorsal and ventral tentacular cirrus, styles missing. Second segment with first pair of elytra, biramous parapodia, and long buccal cirri. Following segments with tapering, short, slightly papillate ventral cirri.

Eighteen pairs of elytra, covering dorsum, on segments 2, 4, 5, 7, then on every second segment to 23, 26, 29, 32, 34, 35, and 38; last three segments cirrigerous; elytral margin with scattered papillae, long at outer lateral margin, shorter at posterior margin; microtubercles rounded, bifid, or branched multifid, becoming gradually larger towards lateral and posterior margin; macrotubercles in a row near posterior margin, cylindrical to club-shaped, distally nodular to spiny. ( Fig. 5 B,C). Cirrigerous segments with distinct dorsal tubercles; dorsal cirri with cylindrical cirrophore, style papillate, tapering.

Parapodia biramous; notopodia with elongate acicular lobe; neuropodia with elongate prechaetal acicular lobe with digitiform supra-acicular process; neuropodial postchaetal lobe shorter than prechaetal lobe, rounded; tips of noto- and neuroacicula penetrating epidermis ( Fig. 5 D). Notochaetae stouter than neurochaetae, with distinct rows of spines and blunt tip ( Fig. 5 E); neurochaetae with distinct rows of spines, tips mainly bidentate with distinct, stout secondary tooth, some lower neurochaetae unidentate ( Fig. 5 F–I).

Measurements. Syntypes (SMF 17300): cs, L 23 mm, W 5 mm for 41 segments ( Fig. 5 A–I); cs, L 17 mm, W 4.5 mm for 38 segments (juvenile with only 15 pairs of elytra!).

Distribution and habitat. Northeast Atlantic, Bay of Biscay; on the cold-water coral Madrepora oculata in 1250 m; up to now known only from the type locality.

Remarks. Acanthicolepis zibrowii n. sp. might be confused with Eunoe oerstedi and Leucia nivea due to its elytral macrotubercles, but one main differentiating character is the number of elytra: A. zibrowii n. sp. is characterised by 18 pairs, while E. oerstedi has 15 and L. nivea 16 pairs (see Figs. 3 B–C, 4B–C, 5B–C and remarks related to E. oerstedi and L. nivea above).

Additionally, A. zibrowii n. sp. differs from E. oerstedi by its bi-and unidentate neurochaetae (versus exclusively unidentate in E. oerstedi , see Figs. 3 F–H, 5F–I), and from L. nivea especially in the shape and distribution of the macrotubercles: cylindrical to club-shaped, distally nodular to spiny, and in a row near posterior margin in A. zibrowii n. sp. and semi-globose, spiny, and present all over the posterior half of the elytron in L. nivea . Another difference to L. nivea is the shape of the microtubercles: rounded, bifid or multifid versus conical to spine-shaped in L. nivea (see Figs. 4 B–C, 5B–C).

The genus Acanthicolepis was revised by Barnich et al. (2000) and includes to date, apart from the new species described herein, only one additional valid species, i.e. A. asperrima ( M. Sars, 1861) . Differentiation of both species is rather easy: in A. asperrima elytra are covered by conspicuous spines with simple, bifid, or multifid tip, becoming gradually larger towards posterior margin, while in A. zibrowii n. sp. elytral tubercles are not spine-shaped, but either rounded, bifid, or branched multifid (microtubercles) or cylindrical to clubshaped, distally nodular to spiny (macrotubercles).

We are aware that a holo- and a paratype should have been designated instead of two syntypes. But both type specimens were originally placed in the same vial and lost all their elytra during fixation. Since they are only slightly differing in size, it was not possible to assign the elytra to the correct specimen.

Figures

FIGURE 3. Eunoe oerstedi (SMF 17527, small specimen). (A) anterior end; (B) left elytron from segment 4; (C) micro- and macrotubercles from same; (D) left elytragerous parapodium from segment 13, posterior view; (E) distal half of long notochaeta; (F) distal part of upper neurochaeta; (G) distal part of middle neurochaeta; (H) distal part of lower neurochaeta. (Scales: A = 2 mm; B = 1 mm; C, E – H = 250 µm; D = 500 µm).

FIGURE 4. Leucia nivea (VM 23936). (A) anterior end; styles of lateral antennae and tip of median antenna missing; (B) right elytron from unknown segment, free in vial; (C) micro- and macrotubercles from same; (D) left parapodium from unknown segment, posterior view; (E) distal half of long notochaeta; (F) tip of same; (G) distal part of middle neurochaeta; (H) tip of same; (I) tip of lowermost neurochaeta. (Scales: A, B = 2 mm; C, F, H, I = 100 µm; D = 1 mm; E, G = 250 µm).

FIGURE 5. Acanthicolepis zibrowii n. sp. (SMF 17300, syntypes). (A) anterior end of large syntype, styles of left lateral and median antenna, and of tentacular cirri and right dorsal cirrus missing; (B) right anterior elytron from unknown segment, free in vial; (C) micro- and macrotubercles from same; (D) right elytragerous parapodium from segment 9 of large syntype, posterior view; (E) distal half of long notochaeta; (F) distal part of middle neurochaeta; (G) tip of same; (H) tip of upper neurochaeta; (I) tip of lower neurochaeta. (Scales: A = 2 mm; B = 1 mm; C = 250 µm; D = 500 µm; E, F = 100 µm; G – I = 50 µm).