Diopatra hektoeni Paxton & Arias 2017, sp. nov

Diopatra hektoeni sp. nov

Figures 2 F–G, 4–6; Table 1

? Epidiopatra hupferiana hupferiana.— Kirkegaard 1988: 31 (Cape Verde Islands); López & San Martín 1992: 166 (Cape Verde Islands).?Not Augener, 1918.

? Epidiopatra hupferiana.— Rullier 1964: 184 (Cape Verde Islands); Núñez et al. 1999: 139 (Cape Verde Islands).?Not Augener, 1918.

Material examined. Type material. Holotype: (MNCN 16.01 /17811). Ponta Preta, Sal Island, Cape Verde Islands, West Africa, 16°36’N – 22°55’W, depth 1–2 m, coll. A. Arias, 0 5 Jul 2013; paratypes (6 specimens): 3 wet specimens (MNCN 16.01 /17812; MNCN 16.01 /17813; AM W.49211); 3 on SEM stubs (MNCN 16.01 /17814; MNCN 16.01 /17815; AM W.49212), same data as holotype.

Type locality. Eastern North Atlantic, Cape Verde Islands, Sal Island, Ponta Preta, 16°36’N – 22°55’W, depth 1–2 m.

Diagnosis. Prostomium anteriorly rounded with two subulate frontal lips. Palps to chaetiger 1, antennae to 3– 5; palpophores with three to four rings, antennophores with four to five rings, both with long lateral projections. Nuchal grooves crescentic; peristomial cirri absent. Anterior four to five pairs of parapodia with bidentate pseudocompound hooks with very long pointed hoods; single postchaetal lobes. Ventral parapodial lobes absent, ventral cirri on four to five chaetigers. Bidentate subacicular hooks from chaetiger 10–11, becoming tridentate in median region, thereafter again bidentate; pectinate chaetae with 15–20 teeth; spiralled branchiae, first on chaetiger 4–5, last on chaetiger 30.

Description. Holotype almost complete, 16 mm long for 67 chaetigers, 0.8 mm wide; paratypes 13–18 mm for 62–75 chaetigers, 0.8–0.9 mm wide. Ethanol stored specimens overall whitish, with pale brown bands on peristomium and anterior dorsum (Fig. 2 F).

Prostomium (Fig. 4 A) anteriorly rounded with two subulate frontal lips separated by a small gap. Ventral upper lips oval with papilla-like median section between lips; lower lip without median section (Fig. 4 B). Palps reaching to chaetiger 1, lateral antennae to chaetiger 4–5, median antenna to chaetiger 3–4; palpophores with two to three proximal rings, antennophores with three to four proximal rings, both with a longer distal ring. Ceratophores with slender lateral projections ending in fine tips. Palpophores with two to three projections, lateral antennophores with three to four on inner side and median antennophore with three to four on inner and outer side (Fig. 4 C). Ceratostyles with irregularly distributed slightly raised circular sensory buds (Fig. 4 D). Styles tapering to distal end, with pointed tips. Nuchal grooves crescentic (Fig. 4 C). Peristomium slightly shorter than first chaetiger; peristomial cirri absent.

First four to five pairs of parapodia modified, slightly prolonged and directed anteroventrally with rounded prechaetal lobe and single subulate postchaetal lobe. Thereafter prechaetal lobe becoming reduced, absent from about chaetiger 8–10. Postchaetal lobe becoming smaller but remaining as small knob into posterior region. Dorsal cirri subulate, attaining greatest length in branchial region, thereafter gradually shortening, becoming very slender posteriorly; ventral cirri subulate on anterior four to five chaetigers, then replaced by ventral glandular pads. Ventral lobe absent. Spiralled branchiae from chaetiger 4–5, best developed on chaetigers 5–8 with up to seven whorls of filaments on thick stem (Fig. 4 E); most anterior branchiae slightly overlapping medially or extending to first chaetiger when extended forwards. Thereafter length of branchiae and number of filaments decreasing gradually, absent from chaetiger 30.

Modified parapodia (chaetigers 1–4 or 5) with one to two slender upper simple limbate chaetae and four to five pseudocompound bidentate hooks with very long pointed hoods and shafts with two rows of spines (Fig. 5 A, B); shafts of about equal thickness, with inferiormost two chaetae only slightly thinner than superior (Fig. 6 A).

Unmodified parapodia (chaetiger 5–6 onwards) with pectinate and limbate chaetae (Fig. 5 C). Pectinate chaetae slightly oblique with 15–20 teeth (Fig. 5 D–F), distal part of chaetae at times rolled and several chaetae wrapped around each other (Fig. 5 E), two to five pectinate chaetae per parapodium in median body region. Limbate chaetae becoming strongly serrated in median region (Fig. 5 C, D), replaced by hooded subacicular hooks from chaetiger 10–11; subacicular hooks initially bidentate, developing small third median tooth from chaetiger 15–16 (Fig. 6 B), best developed from chaetiger 20–40 (Fig. 6 C), then becoming smaller and disappearing to return to bidentate state (Fig. 6 D) to end of body. Pygidium with four anal cirri; larger dorsal ones about as long as pygidium, ventral ones very short.

Mandibles and maxillae not examined for fear of damaging small specimens. Tube thin, secreted inner layer covered with mud and some vegetal material attached at angle on distal part, proximal part paper-like (Fig. 2 D).

Etymology. The new species is dedicated to Martin Mejdell Hektoen, with our thanks for sharing information, particularly his discovery of tridentate subacicular hooks in onuphids.

Remarks. Diopatra hektoeni sp. nov. is so far the only known species of Diopatra, having tridentate subacicular hooks in a short region of its body. It can further be distinguished from other Diopatra species lacking peristomial cirri by the following combination of characters: having branchiae for an extended region, pointed lateral extensions on its palpophores and antennophores, and bidentate pseudocompound hooks with very long hoods (Table 1).

Some specimens reported as Epidiopatra hupferiana (Rullier 1964; Núñez et al. 1999) and E. hupferiana hupferiana (Kirkegaard 1988; López & San Martín1992) from Cape Verde Islands are possibly members of the new species but the brief records did not allow us to draw any firm conclusions.

Distribution. Diopatra hektoeni sp. nov. is only known from its type locality but may be more widespread.