Rhodinicola gibbosus Bresciani, 1964

Kim, Il-Hoi, Sikorski, Andrey, O’Reilly, Myles & Boxshall, Geoff A., 2013, Copepods associated with polychaete worms in European seas, Zootaxa 3651 (1), pp. 1-62 : 15-19

Rhodinicola gibbosus Bresciani, 1964

Rhodinicola gibbosa Bresciani, 1964a: 226 , figs. 2–5.

Material examined: 1 ♀ (dissected and figured) from Praxillella praetermissa (Malmgren, 1866) ; Troll Vest Stn 16-2 (60.76ºN, 3.445ºE), depth 327 m, 20 May 1995.

1 ♀ from P. praetermissa ; Korsfjord, Stn 1-1 (70.237ºN, 23.244ºE), depth 160 m, 06 November 2007; BMNH Reg. No. 2012.1370 .

1 ♀ detached in sample from unknown host; Barents Sea, depth unknown, 19 May 1995; BMNH Reg. No. 2012.1371 .

1 ♀ detached in sample from unknown host; “Resi Stangnes 06”, Stn 5-3/4 (68°48.459’N, 16°36.753’E), depth 74 m, 28 June 2006; BMNH Reg. No. 2012.1372 .

1 ♀ detached in sample from unknown host; 69º19’01”N, 33º32’28”E, depth 282 m, 24 May 1995; BMNH Reg. No. 2012.1373 .

1 ♀ detached in sample from unknown host; Motovsky Gulf, Stn 28-2 (69°35.521’N, 33°09.318’E), depth 226 m, 13 August 2003; BMNH Reg. No. 2012.1374 .

Female. Body ( Fig. 7A ) elongate and consisting of cephalothorax, 4 pedigerous somites, genital doublesomite, and 3 free abdominal somites, lacking conspicuous prosome-urosome division. Somites clearly divided by deep constrictions between them. Body length of adult variable: 4.32 mm in dissected specimen, but 6.28 mm in largest specimen from Barents Sea. Cephalothorax triangular in dorsal view, 645×727 µm. Cephalothorax and first to third free metasomal somites (second to fourth pedigerous somites) usually with posterodorsal sub-globular tubercle in midline (tubercles weakly expressed in some specimens). Second to fifth pedigerous somites 600×691, 655×673, 656×618, and 545×600 µm, respectively. Genital double-somite wider than long, with large, paired posteroventral expansions, each expansion distally incised and with genital aperture located within incision; expansions ornamented with rows of minute spinules ( Fig. 7B ) on ventral surface. Abdomen gradually narrowing from anterior to posterior: first free abdominal somite wider than long, second 275×300 µm, anal somite 215×220 µm, with several patches of minute spinules on ventral surface. Caudal ramus ( Fig. 7C ) directed posterolaterally, tapering, 208×64 µm (ratio 3.25 1), with 7 naked setae including small, setule-like outer proximal seta (seta I); largest distal seta 333 µm long. Egg sac ( Fig. 7D ) 2.85× 0.35 mm; eggs arranged in 3 or 4 rows.

Rostrum as semicircular protuberance on frontal margin ( Fig. 7E ). Antennule ( Fig. 7E ) 308 µm long and 5- segmented; first and second segments expanded, distinctly broader than distal 3 segments; armature formula 3+spine, 10+spine, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; spine on first and second segments short, with spinulate lateral margins; first segment with large patch of densely-set minute setules on ventral surface; setae on all segments naked. Antenna ( Fig. 7F ) 4-segmented; segments becoming shorter and narrower from proximal to distal; first segment (coxa-basis) smooth and unarmed; second segment (first endopodal segment) unarmed but with patch of spinules sub-proximally and rows of spinules distally; third segment with 1 distal spinulose claw and several leaf-like hyaline extensions on mediodistal surface; terminal segment 23×12 µm, armed with 2 spinulose claws, 2 long setiform claws, and 2 small subdistal setae.

Labrum ( Fig. 7G ) with large patches of numerous spinules on each disterolateral area and broad median ridge extending slightly beyond posterior margin. Mandible ( Fig. 7H ) digitiform with distal membranous extension; armature consisting of distal spine (spine distally bifurcate or trifurcate), and large, transparent plumose seta subdistally. Maxillule lobate bearing 4 naked distal setae, one spiniform. Maxilla ( Fig. 8A, B ) 2-segmented; proximal segment very broad and unarmed; distal segment stout, distally ornamented with dense covering of minute spinules, armed with 2 claw-like processes, and 1 short but thick medial seta. Maxilliped ( Fig. 8C ) 4- segmented; first segment unarmed; second segment with 2 unequal naked setae on medial margin and patch of spinules on medial surface; third segment unarmed; terminal segment tapering, with 2 large naked setae, 1 small spine, and spiniform terminal claw ornamented with spinules along medial margin; terminal claw articulated at base.

Legs 1–4 ( Fig. 8D–G ) with 3-segmented rami; all rami becoming narrower from proximal to distal, with spinules on outer margin and patches of spinules on posterior (dorsal) surface (indicated by dotted circles in Fig. 8D–G ). Coxa of legs 1–4 with 1 mediodistal patch of spinules close to inner seta. Basis of leg 1 with posterior patch of spinules between bases of rami. Basis of legs 2–4 with 2 posterior patches of spinules. Setae small on both rami of legs 1–4. Armature formula of legs 1–4 as follows:

Leg 1: coxa 0-1; basis 1-0; exp. I-0; I-1; II, 2, 2; enp. 0-0; 0-1; I, 2, 2

Leg 2: coxa 0-1; basis 1-0; exp. I-0; 0-1; III, 2, 4; enp. 0-1; 0-2; 1, 2, 2

Leg 3: coxa 0-1; basis 1-0; exp. I-0; I-1; I, 2, 5; enp. 0-1; 0-2; 0, 1, 2

Leg 4: coxa 0-1; basis 1-0; exp. I-0; I-1; II, 1, 5; enp. 0-1; 0-2; 0, 1, 2

Leg 5 ( Fig. 8H ) 2-segmented but proximal protopodal segment incorporated into somite, with 1 posterolateral seta; free distal segment (exopod) roughly rectangular, wider than long, with 4 setae and several patches of spinules. Leg 6 not seen.

Remarks. The large subdistal seta on the mandible was omitted from the original description, probably due to its transparency. We were able to find only four distal elements on the maxillule and were unable to confirm the presence of a subdistal seta as illustrated by Bresciani (1964a). Some of the small setae on the rami of swimming legs were also apparently overlooked in the original description. Our specimens were all taken from the type host, the maldanid P. praetermissa , or were found detached in macrobenthos samples.

Figures

FIGURE 7. Rhodinicola gibbosus Bresciani, 1964, female. A, habitus, dorsal; B, urosome, ventral; C, left caudal ramus, dorsal; D, egg sac; E, rostrum and antennule; F, antenna; G, labrum; H, mandible; I, maxillule. Scale bars: A, D, 0.5 mm; B, 0.2 mm; C, 0.1 mm; E, 0.05 mm; F–I, 0.02 mm.

FIGURE 8. Rhodinicola gibbosus Bresciani, 1964, female. A, maxilla, medial; B, distal segment of maxilla, ventral; C, maxilliped; D, leg 1; E, leg 2; F, leg 3; G, leg 4; H, leg 5. All scale bars: 0.02 mm.