Dipolydora paracaulleryi Bick, Guggolz & Götting, 2014, sp. nov.

Dipolydora paracaulleryi sp. nov.

(Figures 7–10)

Polydora (Polydora) caullery.— Hartmann-Schröder, 1979: 88.

Holotype: NE Atlantic Ocean, Expedition DIVA 3, cruise METEOR ME 79-1: Great Meteor Seamount, 29°44.13’N 028°24.91’W, station 656, epibenthic sledge, depth 283.3 m, 18-Aug-2009, 96% ethanol, 1 af (ZSRO- P2305).

Paratypes: NE Atlantic Ocean, Expedition DIVA 3, cruise METEOR ME 79-1: Great Meteor Seamount: 29°44.13’N 028°24.91’W, station 656, epibenthic sledge, depth 283.3 m, 18-Aug-2009, 96% ethanol, 1 af SEM (ZSRO-P2304); 29°41.84’N 028°22.55’W, station 645, grab, depth 295 m, 18-Aug-2009, 96% ethanol, 1 af (ZSRO-P2306). Little Meteor Seamount: 29° 36.29' N 028° 59.68' W, station 624, grab, depth 274.2 m, 17-Aug- 2009, 96% ethanol, 1 af (ZSRO-P2303). Atlantic Seamount cruise, METEOR cruise 9c, Great Meteor Seamount: 29°57.7’N 028°35.1’W, station 151a, Agassiz trawl, depth 305–316 m, 16-Jul-1967, formalin, 1 af (ZMH-P17290).

Additional material examined. NW Atlantic Ocean: Great Bank of Newfoundland, depth 121–148 m, 12- Sep-1993 – 15-Sep-1993, 2 af (SMF 5133); North Sea: German Bight, Borkum Riff, depth 27 m, 23-Apr-1968, 3 af (SMF 6186), depth 26 m, 22-Apr-1968, 2 af (SMF 6187); German Bight, Langeoog, 1967, 1 af (SMF 6189); Mediterranean Sea: Gulf of Marseille, 5-Nov-1982, 2 af (SMF 16028).

Diagnosis. Anterior margin of prostomium truncated, not or only slightly projecting beyond the peristomium. Caruncle large and triangular, encompassing bases of first notopodia, extending posteriorly to chaetiger 2 (Figures 7 A, 8A–B). Occipital antenna absent. Eyes absent in adults. Nuchal organ as ciliary bands on either side of caruncle (Figure 8 A). First notopodia with few capillary chaetae (Figures 7 A, 8A–B). Chaetiger 5 with dorsal fascicle of fringed geniculate chaetae, bushy-topped modified spines with accessory lateral flange, and ventral fascicle of fringed capillaries (Figures 7 C, F, 8C, 9). Dorsal branchiae from chaetiger 7 to maximally chaetiger 12. Bidentate hooded hooks from chaetiger 7, accompanied by one capillary in inferiormost position (Figure 7 C, E). Posterior notopodia with bundles of thick acicular spines (Figure 7 D). Pygidium with 4 lobes, ventral lobes larger, more expanded, touching each other, dorsal lobes smaller, distinctly separated (Figure 7 D).

Description. Small species; holotype anterior fragment with 14 chaetigers, about 2 mm in length and 0.35 mm wide. Other examined anterior fragments with 12–14 chaetigers, 1.1–1.2 mm in length and 0.1–0.3 mm wide. One complete specimen 1.2 mm long and 0.2 mm wide for 29 chaetigers.

Prostomium with truncated, indistinctly incised anterior margin, not or only slightly projecting beyond the peristomium anteriorly, laterally separated from peristomium by a narrow furrow (Figure 7 A–B, 8A–B); posterior part of prostomium with slight elevation, extending posteriorly to chaetiger 2 as large and triangular caruncle; caruncle encompassing bases of first notopodia (Figures 7 A, 8A–B). Anterior fragments without eyes; one complete specimen with three black eyes, anterior eyes paired, posterior eye in the middle of prostomium directly behind the anterior pair. Occipital antenna absent. Palps arising at the end of the furrow between prostomium and peristomium, extending posteriorly for about 10 to 15 chaetigers (Figure 10 A). Nuchal organ as ciliary bands laterally to caruncle until the second chaetiger (Figures 7 A, 8A–B).

First parapodia with 2–4 notopodial capillary chaetae, neuropodial capillaries more numerous, parapodia 2 to 4 and 6 with fringed capillaries; notopodial capillaries of superior longitudinal row or fascicle distinctly longer than those of transverse row (Figures 7 A, 8A); medium and posterior notopodia with acicular spines, on medium chaetigers only one or few spines additionally to capillaries, spines replacing capillaries on posterior notopodia completely and forming a curved row (Figure 7 D). Bidentate hooded hooks from chaetiger 7, numbering up to 5 per fascicle, hooded hooks accompanied throughout by one thin capillary in inferiormost position, hooks without constriction on shaft (Figure 7 E).

Both notopodial and neuropodial lamellae relatively small, on anterior chaetigers notopodial lamellae triangular and neuropodial lamellae oval (Figure 8 B); in posterior parapodia both neuropodial and notopodial lamellae narrow; praechaetal lamellae not developed.

Dorsal, flattened branchiae from chaetiger 7 (Figure 8 D), reaching full size by chaetiger 8, continuing to chaetigers 11 or 12, reaching midline dorsally and touching from chaetiger 8 to 11 or 12; basally fused to notopodial postchaetal lamellae.

Chaetiger 5 modified, but not larger than chaetigers 4 and 6 (Figure 7 A–C), lacking postchaetal lobes (Figure 8 C); superior dorsal fascicle of two broad, fringed, geniculate chaetae, two major spines, and ventral fascicle of 4 to 6 fringed capillaries; major spines with large, beak-like curved end bearing crest of bristles and lateral accessory flange, companion capillaries absent (Figures 8 C, 9).

Glandular pouches present on chaetigers 6 and 7, ventrolaterally; most striking after methyl green staining (Figure 10 B–C).

Gizzard-like structure absent in anterior part of digestive tract.

Pygidium with 4 lobes, ventral lobes larger, more expanded, touching each other, dorsal lobes smaller, distinctly separated (Figure 7 D).

Pigmentation. Body generally opaque white in ethanol. Complete specimen with dorsolateral and lateral intersegmental brown pigment on anterior chaetigers up to segment 10. Additionally, neuropodia of chaetiger 6 brown-rimmed.

Methyl green staining pattern. Anterior rim of the prostomium, peristomium and anal cirri most intensively stained; bands of scattered dots both on borders of chaetiger 6 and 7 ventrally (Figure 10 A–C), expanded in the regions of the glandular pouches on chaetiger 6 and 7 (Figures 7 B, 10B); in addition, border from between chaetiger 9/10 to about 12/13 deep blue ventrally, some deep blue spots scattered on posterior part of prostomium and dorsum anteriorly (Figure 10 A).

Ecology. Dipolydora paracaulleryi sp. nov. was found on the Great and Little Meteor Seamounts in coral and crushed shell gravel in about 300 m depth.

Geographical distribution. NE Atlantic: Great Meteor Seamount (type locality) and Little Meteor Seamount.

Etymology. The species name is derived from D. caulleryi, the closest relative to D. paracaulleryi sp. nov.

Remarks. Dipolydora paracaulleryi sp. nov. is a member of the D. armata / D. caulleryi group owing to the presence of distinct modifications of the major spines of the fifth chaetiger and the heavy, protruding spines in posterior notopodia (see Blake 1996). Seven species belong to this group. But Dipolydora paracaulleryi sp. nov. closely resembles only D. caulleryi (Mesnil, 1897). The two species possess unidentate, falcate, bristle-topped spines on chaetiger 5, and branchiae and hooded hooks start on chaetiger 7. Another very similar species is D. blakei (Maciolek, 1984) but this species possesses 3–4 falcate spines on chaetiger 5 with a large lateral tooth, rather than only 2 spines with a lateral flange, and a pygidium with 2 lateral lobes and a cup-shaped pygidium respectively, rather than a pygidium with one pair of dorsal and one pair of ventral lobes (Maciolek 1984, Radashevsky & Simboura 2013). The number of superior geniculate chaetae (4–6) on chaetiger 5 of D. blakei is greater compared with D. paracaulleryi sp. nov. (only 2).

Dipolydora paracaulleryi sp. nov. differs from D. caulleryi in having 2 unidentate, falcate, bristle-topped spines rather than 3 or 4, and is distinctly smaller (8 mm long for D. caulleryi opposed to about 2 mm for D. paracaulleryi sp. nov.). Several important diagnostic characters such as the number of chaetigers, the length of the caruncle, the shape of postchaetal lobes, and number and shape of pygidial lobes have not been described in the original description of D. caulleryi. It is unknown whether type material still exists, and if so, where it has been deposited. For this reason, further potential distinctions between D. caulleryi and D. paracaulleryi sp. nov. cannot be indicated. Moreover, descriptions of specimens assumed belonging to D. caulleryi vary conspicuously. Pettibone (1954) described D. caulleryi specimens of 50 mm length and 2.2 mm width, with a caruncle extending to chaetiger 4 to 6, and 0 to 6 eyes, branchiae to first appear on chaetiger 7 or 8, exhibiting 3–12 major spines on chaetiger 5 without companion capillaries, and 2 to 3 neuropodial hooded hooks. Specimens described by Blake (1971) are of comparable size, possess a caruncle extending to chaetiger 3 or 4, possess about 13 neuropodial hooded hooks, and major spines of chaetiger 5 are arranged in an elevated semicircle with capillary companion chaetae. The investigated specimens from the North Sea and NW Atlantic Ocean correspond with Blake’s (1971) description, though companion chaetae on chaetiger 5 are absent. As the descriptions by the two authors differ significantly both from each other and from the original description it is assumed here that descriptions by Mesnil (1897), Pettibone (1954) and Blake (1971) refer to different species.

Dipolydora caulleryi specimens from the Mediterranean Sea, also investigated during this study, resemble D. paracaulleryi sp. nov. in having 2–3 major spines with lateral flange; length and shape of the caruncle are also similar. But these slightly larger specimens possess 3 geniculate notochaetae and 8–10 ventral capillaries on chaetiger 5 (opposed to 2 and 4–6 chaetae respectively in D. paracaulleryi sp. nov.) and only 3–4 neuropodial hooded hooks (4–5 in D. paracaulleryi sp. nov.). The identity of the Mediterranean specimens cannot be clarified based on current knowledge. A comparative study of specimens of D. caullery and morphologically similar species from different localities is required to learn about their infraspecific variability and to identify reliable distinguishing characters for species of this species complex.