Pholoe pallida, CHAMBERS, 1985

PHOLOE PALLIDA CHAMBERS, 1985 View in CoL

( FIGS 5, 7)

Pholoe pallida Chambers, 1985: 21 View in CoL , figs 13 c–d, 18 e–h, pl. A: 3–4, pl. B: 3–4.

Pholoe cf. anoculata Christie, 1982: 284 View in CoL [synonymy adopted from Chambers (1985)].

Type locality: Great Britain, Berwickshire , off St. Abbs, 56°4’N, 2°7’W GoogleMaps .

Type material: Holotype: Great Britain, Berwickshire , off St. Abbs, Firth of Forth, sludge dumping ground, station 17, 56°4’N, 2°7’W, coll. A. Mackie, 1 af, dissected elytron ( RSM Z. 1983.84.1), wet slide with dissected elytron RSM Z. 1983.84.12 GoogleMaps ). Paratype: UK, Berwickshire , off St. Abbs, 15 March 1911, coll. Irish Fisheries, 1 af ( RSM Z. 1983.84.2) .

Non-type material: North Atlantic Ocean: Norway: 60°42.68’N, 3°30.74’E, Stn 44–5, 14 May 1998, depth 319 m, 1 af ( ZSRO-P700 ) GoogleMaps , 60°47.31’N, 2°54.82’E, Stn 7-5, 16 May 1998, depth 181 m, 1 ( ZSRO-P701 ) GoogleMaps ; Oslofjord, 59°38.694’N, 10°36.700’E, station 10–13 PolySkag , depth 130 m, gravel/mud/rocks, 2 af ( ZSRO-P2553 , 2554 ) GoogleMaps . North Sea: 59°3.15’N, 1°1.59’W, S of Shetland Islands, Apr / May 1993, depth 130.4 m, 5 af, 5 mf ( RSM Z. 1996.4.36); 58°42’N, 1°17’E, Brae Oilfield, station MBI 2, 2 af ( RSM Z. 1984.4.2.), MBI 3, 4 af ( RSM Z. 1984.4.3.), MBI 4, 1 af, 4 mf ( RSM Z. 1984.4.4.), MBI 5, 2af, 5 mf, 1 pf ( RSM Z. 1984.4.5.), MBI 8, 1 af ( RSM Z. 1984.4.6.), MBI 9, 7 af, 7 mf ( RSM Z. 1984.4.1.); 57° 44’ N 0° 64’ E, Forties Oilfield, StF78, depth 114 m, 1 af, 4 mf, wet slide ( RSM unregistered); UK: 57°56.892’N, 2°0.375’W, Outer Moray Firth, Smilers Hole, OMFA T4.4#2, DTI strategic Environmental assessment area 5, 22 September 2003, depth 118.3 m, muddy sand, 2 af ( RSM Z.2009.5.137.); Berwickshire, off St. Abbs , 56°4’N. 2°7’W, sludge dumping ground, November 1981, station 23 and 15, 3 af, 4 mf, 1pf ( RSM Z.1983.84.1-4); 55°4.5’N, 1°15.8’W, off Northumberland coast, 22 January 1982, depth 50 m, 2 af, 1 mf, wet slide with 2 af ( RSM Z.1983.85) GoogleMaps . Specimens collected for DNA work, fixed in 96% ethanol, morphologically examined: Great Britain: South of Shetland Islands, 57.855592, -2.87422 (57°51.33552’N, 2°52.4532’W), 17 July 2008, depth 90–98 m, silty clay ( ZMBN 127131 View Materials , 127132 View Materials ) GoogleMaps . Sweden: Koster Area , 58.87, 11.10 (58°52.2’N, 11°6’E), April 2005, depth 60–80 m ( ZMBN 127133 View Materials , 127134 View Materials ) GoogleMaps , mellan Hällsöarna , 58.87, 11.10 (58°52.2’N, 11°6’E), April 2005, depth 70–80 m ( ZMBN 127135 View Materials , 127136 View Materials , 127137 View Materials , 127138 View Materials ) GoogleMaps . Norway: Sogn og Fjordane, Hyllestad , 61.1339, 5.16632 (61°8.034’N, 5°9.979’E), 22 July 2012, depth 631–644 m ( ZMBN 127140 View Materials ) GoogleMaps .

Diagnosis: Specimens without pigment; eyes absent; dorsal and ventral tentacular cirri smooth, cirriform, dorsal one only slightly longer; mid-dorsum with almost complete cover by elytra; elytral papillae strong with robust base; facial tubercle present, often with conspicuously wide base; lateral antenna present; parapodia without stylodes; neurochaetae heterogomph compound chaetae with two parallel rows of short teeth along the blade (only seen in SEM).

Description: Holotype anterior fragment of 15 chaetigers, 2.2 mm long, 1.1 mm wide. Largest complete specimen fixed in formalin with about 53 chaetigers 6.9 mm in length and 1.0 mm wide. Other complete specimens 5.5 mm long and 1.0 mm wide, at 45 chaetigers.

Body short, linear, depressed ( Fig. 5B, C); ventral surface with evenly distributed short papillae. Mid-dorsum completely covered by elytra; in larger specimens, anterior two to three pairs of elytra leaving a narrow mid-dorsal gap uncovered; in smaller specimens, complete cover all along the body ( Fig. 5A–C). First pair of elytra rounded, in succeeding segments reniform and anteriorly notched ( Fig. 5A), in posterior segments transversally elongated ( Fig. 5D); segments without elytra with nodular lobes in the position of elytrophores; first elytron with marginal, submarginal and central papillae, only inner margin without papillae ( Fig. 5B), in all succeeding segments elytra with several marginal and submarginal papillae along the lateral and the posterior margins ( Fig. 5D); elytral papillae robust with strong base, tip slender and slightly knobbed ( Fig. 5E); elytral surface without pigment.

Prostomium with smooth cirriform, slightly capitate median antenna without articulations ( Fig. 5A, A′, A″); lateral antennae present ( Fig. 5A′); eyes absent. Facial tubercle present, prominent, with wide base wide with few papillae ( Fig. 5A, A′, A″); mouth opening on ventral side with slightly elongated papillae.

Tentacular segment achaetous, with two pairs of cirriform tentacular cirri rising from a tentaculophore ( Fig. 5A, A′, A″); dorsal tentacular cirrus slightly longer than ventral one, both tentacular cirri cirriform ( Fig. 5A, B). Palps massive, tapering ( Fig. 5A).

Parapodia biramous ( Fig. 7); notopodium shorter than neuropodium, notopodium of conical shape at the end, without terminal papillae; few (one to three) strong papillae present on its anterior and posterior lower edge ( Fig. 7); neuropodium tapering, longer than notopodium, anterior surface almost smooth, posteriorly with evenly distributed short simple papillae, long terminal papillae (stylodes)absent( Fig.7); cirriform ventral cirrus present on neuropodia, ventral cirrus at first chaetiger (buccal cirrus) anteriorly oriented and considerably longer than on following chaetigers, ventral cirri otherwise laterally oriented. Both parapodial lobes bearing single stout acicula; notopodium with long, spinous capillaries and short, stout, geniculate capillaries with serrations; neurochaetae compound falcigerous heterogomph chaetae with two rows of short teeth on the blade, fine serrations near the distal end of the shaft present (see: Chambers 1985: pl. B, 4).

Pygidium with pair of long cirriform to thread-like anal cirri, terminoventrally attached ( Fig. 5C).

Pigmentation: Preserved specimens without pigment. Photography of live specimen shows pink colour inside the first three segments (which might not be pigment of the worm itself).

Ecology: The species was found in the North Sea in water depths between 50 and 644 m, in silty clay and muddy sand.

Geographical distribution: The species was recorded from the North Sea as far north as southern Norway, in the central North Sea, near the British coasts and in the Skagerrak.

Remarks: Pholoe pallida is one of the Pholoe species exhibiting morphological characters allowing a straightforward identification. These characters are the absence of eyes, the presence of distinct elytral papillae with robust base ( Fig. 5E) and a conspicuous facial tubercle with wide base in large specimens ( Fig. 5A). Also, the presence of lateral antennae could be documented using CLSM ( Fig. 5A, A’) and thus contradicting the statement in the original description of lateral antennae being absent. The presence of two rows of teeth on the blades of compound neurochaetae has been documented by a SEM micrograph to be found in Chambers (1985). This character is shared with P. assimilis and P. minuta , whereas other Pholoe spp. from European waters exhibit one row of teeth on the blades. Pholoe assimilis and P. minuta can be distinguished from P. pallida by the absence of the facial tubercle.