Pholoe petersenae, Ravara, Ascensão & Cunha, Marina R., 2016

Ravara, Ascensão & Cunha, Marina R., 2016, Two new species of scale worms (Polychaeta: Aphroditiformia) from deep-sea habitats in the Gulf of Cadiz (NE Atlantic), Zootaxa 4097 (3), pp. 442-450 : 446-448

Pholoe petersenae sp. nov.

Figure 3

Type material. Atlantic Ocean. Gulf of Cadiz (MV): Captain Arutynov MV, St MSM01-3_274, 1321 m, 1 spm ( NHMUK 2016.348, holotype); St MSM01-3_180, 1323 m, 3 spms ( NHMUK 2016.349-351); St MSM01-3_190.1, 1322 m, 3 spms ( DBUA 0001727.03); St MSM01-3_218, 1318 m, 13 spms ( DBUA 0001727.04); St. MSM01- 3_225, 1320 m, 1 spm ( DBUA 0001727.05); St TTR14_AT546, 1345 m, 3 spms ( DBUA 0001728.01); Darwin MV, St B09-14b_02W, 1100 m, 1 spm ( DBUA 0001729.01); Carlos Ribeiro MV, St MSM01-3_184, 2204 m, 1 spm ( DBUA 0001727.06).

Additional material. Pholoe anoculata , Atlantic Ocean, off New England, W of Atlantis Canyon, St S 1 4, 39 º56’30’’N, 70º3954’’W, 400 m, 28-08-1962, 1 spm (LACM-AHF Poly 0069; paratype).

Description. The holotype measures 2.13 mm long and 0.30 / 0.91 mm wide without and with parapodia respectively, for 26 segments. Body of uniform width, compressed dorsoventrally, without pigmentation pattern or dorsal tubercules. Globular papillae present on parapodia and ventral surface. Fifteen (?) pairs of elytra on segments 2, 4, 5, 7, alternating to 23, then on every segment to end of body; completely covering dorsum and parapodia. All elytra oval, transparent, delicate, with smooth dorsal surface and a few cirriform papillae with blunt expanded tip bearing cilia on outer border ( Fig. 3 D, E). Prostomium subsphaerical, bilobed anteriorly; without eyes ( Fig. 3 A). Anterior lobes with terminal conical peaks protruding lateroventrally to median antenna. Median antenna long, smooth, gradually tapering, with large ceratophore inserted in median notch of prostomium. Palps smooth, stout, gradually tapering, inserted ventrolaterally on prostomium and much longer than median antenna. First segment fused to prostomium, achaetous; tentacular cirri inserted between lateral antennae and palps, subequal and similar in length to median antenna, smooth. Facial tubercle very small ( Fig. 3 B). Pharynx with 16 terminal papillae and two pairs of light brown jaws. Ventral cirri of buccal segment large, tapering into filiform tips, displaced medially. Parapodia relatively long, biramous, covered by globular papillae and stylodes. Notopodia much smaller than neuropodia, enlarged basally and distally pointed; neuropodia conical ( Fig. 3 C). Notochaetae long spinulose capillaries, straight or geniculate ( Fig. 3 F). Neurochaetae long, compound, stouter than notochaetae; shafts with three subdistal rows of spines; blades very long and thin, minutely spinulated, with slightly falcate tips ( Fig. 3 G). Pygidium with a pair of anal cirri.

Type locality. Gulf of Cadiz (NE Atlantic), Captain Arutyunov mud volcano, 35º39.740'N, 07º19.960'W, 27 April 2006, MSM01 Leg 3 (RV Maria S. Merian ).

Distribution. Northeast Atlantic (Gulf of Cadiz).

Habitat. Found in sediment samples taken from active methane seepage sites in the craters of Captain Arutyunov MV and Carlos Ribeiro MV, sympatric to diverse assemblages of chemosymbiotic species ( Siboglinidae tubeworms, Thyasiridae , Vesicomyidae and Solemyidae bivalves; see Rodrigues et al. 2013 for a complete species list). An additional specimen was retrieved from wood colonization experiments which were deployed for about two years on the crater of Darwin MV typically covered by carbonate slabs and clumps of bathymodiolin mussels. Water depth range from 1100 to 2204 m.

Etymology. The species epithet is given in memory of Dr. Mary Petersen who gathered a large amount of information on Pholoe species while revising the genus for an unpublished monograph.

Remarks. Besides P. petersenae sp. n., there are presently four described species of Pholoe lacking eyes, two of which are recorded from the Atlantic Ocean, P. pallida Chambers, 1985 and P. anoculata Hartman, 1965 . Pholoe pallida was first described from off St. Abbs ( Scotland) and it is only known from the North Sea area at near-shore depths ( Chambers & Muir 1997; Petersen 1998), although Chambers (1985) refers to a possible confusion between this species and P. m i nu t a, and that all records of the latter require revision. The specimens examined herein were collected in the Gulf of Cadiz at deeper waters, and differ from P. pallida mainly by having prostomial peaks and neuropodia stylodes (both absent on P. pallida ), neurochaetae with longer blades, and cirriform instead of flaskshape papillae on the elytra margins. Pholoe anoculata is a western Atlantic species occurring from 400 to 5000 m depth, which like the specimens examined here, have nearly smooth elytra with scattered slender fringing papillae and neurochaetae with longer blades ( Hartman & Fauchald 1971). Our specimens seem to be morphologically closer to this latter species, but differ from it again by having prostomial peaks and neuropodia stylodes and also neurochaetae shafts with subdistal rows of spines instead of being smooth as stated by Hartman and Fauchald (1971). Previous records of P. anoculata from off Northumberland ( UK) ( Christie 1982) were erroneous and were later ascribed to P. pallida ( Chambers 1985) . A review of these and other species, preferably with the inclusion of molecular data, is required to evaluate their phylogenetic relationships and to define their morphological differences.

Figures

FIGURE 3. Pholoe petersenae sp. nov. Paratype (NHMUK 2016.349). A—Anterior end, dorsal view B—Same, ventral view C—Median parapodium, dorsal view, showing stylodes and globular papillae D—Posterior elytron, dorsal view E—Detail of elytral fringing papilla F—Notochaetae G—Neurochaetae. Scale bars (µm): A, B, D = 100, C, E = 50, F, G = 25.