Rhodinicola rugosum ( Giesbrecht, 1895 )

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 : 19-23

Rhodinicola rugosum ( Giesbrecht, 1895)

Seridium rugosum Giesbrecht, 1895: 223 , pl. ix.

Seridium rugosum: Wilson and Illg, 1955: 134 .

Rhodinicola rugosa: Bresciani, 1964a: 232 .

Material examined: 3 ♀ (2 ♀ dissected), attached to fragment of Clymenura Verrill, 1900 ; English Channel off Littlehampton , West Sussex (50 o 40.143’N, 0 o 31.200’W), depth 15 m (sample taken by Hamon Grab), collected by J. Weir at EMU Ltd, 29 September 2004; BMNH Reg. No. 2012.1377 (undissected ♀) .

1 ♀ detached from host; Inner Gabbard Ground off Harwich (51 o 54.07’N, 01 o 45.15’E); depth unknown, recovered by David Hall, 14 June 2000; BMNH Reg. No. 2012.1378 .

1 ♀ attached to Euclymene sp. , Central North Sea , Lundin Block 21-8, Stn 5 (57 o 40.3878’N, 00 o 24.4776’E), depth ~ 104 m, collected by Sue Hamilton, April 2007; BMNH Reg. No. 2013.10 .

3 ♀ attached to Clymenura tricirrata , Central North Sea , Lundin Block 21-8, Stn 6 (57 o 40.8664, 00 o 25.0638’E), depth ~ 104 m, collected by Sue Hamilton, April 2007; BMNH Reg. No. 2012.1379 .

1 ♀ attached C. tricirrata , Central North Sea , Lundin Block 21-8, Stn 14 (57 o 40.3878’N, 00 o 25.0961’E), depth ~ 104 m, collected by Sue Hamilton, April 2007; BMNH Reg. No. 2012.1380 .

1 ♀ detached from host, Central North Sea , Lundin Block 21-8, Stn 15 (57 o 40.2902’N, 00 o 24.6928’E), depth ~ 104 m, collected by Sue Hamilton, April 2007; BMNH Reg. No. 2013.11 .

1 ♀ attached to C. tricirrata , Central North Sea , Lundin Block 21-8, Stn 18 (57 o 39.9607’N, 00 o 24.3614’E), depth ~ 104 m; collected by Sue Hamilton, April 2007; BMNH Reg. No. 2013.12 .

2 ♀ detached but 4 Praxillella affinis in sample, 15 miles east of Harwich , Suffolk (51 o 49.88’N, 01 o 45.07’E), depth 35 m, collected by Tim Worsfold, May 1998; BMNH Reg. No. 2013.13 .

1 ♀ attached to fragment of P. affinis, Hastings , East Sussex, CEFAS Stn 169Y (50 o 44.05’N, 00 o 35.90’E); collected David Hall, July 2001; BMNH Reg. No. 2012.1381 .

Additional records:

North Sea:

1 ♀ detached from host, Golden Eagle Oilfield (Blocks 21/1N, 20/1S) Stn 01-FB, 07 March 2008.

1 ♀ immature from maldanid fragment, Arundel/Farragon Oilfield, Stn A09-22-a, 09 September 2009.

1 ♀ attached to Clymenura sp. , Sycamore Oilfield, Stn ENV-FA, 05 January 2010.

1 copepodite on Clymenura johnstoni (McIntosh, 1915) , Moray Firth, Stn MSS MF1.2 (57 o 51.01’N, 03 20.97’W), depth 64 m; found by Stephen Nowacki, 14 January 2010 .

Western Scotland:

1 copepodite from Clymenura sp. , Fishnish, Isle of Mull, collected by Julian Hunter, 2006.

1 ♀ detached from host, Firth of Clyde , Scotland, Stn G 03-1 (55 o 44.922’N, 04 o 53.110’W) collected David Hall, 26 June 2009 .

1 ♀ attached at setiger 9 (of 10) on anterior fragment of Clymenura sp. , Loch Laxford, SNH Stn 24 (58 o 23.67’N, 05 o 03.76’W); collected Sue Hamilton, 21 October 2009.

1 ♀ Loch Fyne, SEPA Surveillance site (56 o 02.76’N, 05 o 18.89’W), depth 43 m; collected Stephen Nowacki, 11 March 2010 .

1 ♀ Loch Roag , Isle of Lewis, SEPA site at Fuaigh Beag (58 o 12.03’N, 06 o 53.63’W), depth 29 m; collected Stephen Nowacki, 24 July 2012 .

England:

1 ♀ detached but 16 Praxillella affinis (M. Sars, 1872) in sample, 15 miles east of Harwich , Suffolk (51 o 52.16’N, 01 o 45.51’E), depth 35 m; collected by Tim Worsfold, May 1998 .

Ireland:

1 ♀ on maldanid fragment ( Praxillella ?), Northern Irish Sea , Block 109, Stn 3 (53 o 45.27’N, 04 o 07.12’W), depth 46 m; collected by Sue Hamilton, September 1995 .

1 ♀ northern Irish Sea , Block 109, Stn 12 (53 o 54.85’N, 04 o 15.98’W), depth 44 m; collected by Sue Hamilton, September 1995 .

1 ♀ attached to Praxillella sp. ? fragment, Belfast Lough (54 o 42.180’N, 05 o 35.538’ W), depth 25 m; collected by Tim Mackie, 30 April 1999 .

1 ♀ and 2 juveniles attached to Clymenura johnstoni, Stn 619, Irish Sandbanks Survey, collected by Peter Garwood.

1 ♀ detached from host, Arklow Bank, collected David Hall, 05 October 2006.

1 ♀ detached from host, Belfast Lough , EHS Stn F 02-b (54 o 43.47’N, 05 o 34.02’W), depth 36 m; collected by Tim Mackie, 04 April 2008 .

1 ♀ Larne Lough , Stn LL 4-d (54 o 50.35’N, 05 o 47.80’W); depth 5 m; collected by Tim Mackie, 01 November 2008 .

Female. Body ( Fig. 9A, B ) elongate, dorsoventrally depressed, and consisting of cephalothorax, 4 pedigerous somites, genital somite, and 4 free abdominal somites, lacking conspicuous prosome-urosome division. Somites clearly divided by deep constrictions between them. Body lengths of 2 dissected specimens 2.79 and 2.47 mm. Cephalothorax triangular in dorsal view, 412×461 µm, with 1 prominent posterodorsal tubercle ( Fig. 9A ). Second to fifth pedigerous somites 312×486, 369×492, 326×486, and 252×436 µm, respectively; these somites typically rectangular in outline but more sub-circular in inflated specimens, with transverse crease on dorsal surface of each ( Fig. 9A, B ). Genital somite 369×196 µm, width measured across genital prominences ( Fig. 10K ), 424 µm; somite broader anteriorly and narrower posteriorly. Four free abdominal somites 135×233, 129×212, 104×184, and 98×146 µm, respectively. Dorsal suture line incomplete between third abdominal and anal somites. Anal somite characteristically narrower than preceding abdominal somites, with patch of minute spinules on ventrodistal surface near base of caudal ramus ( Fig. 9C ). Caudal rami divergent; each ramus gradually narrowing from proximal to distal, 138×48 µm (ratio 2.88:1), with 6 setae and 1 minute outer proximal seta ( Fig. 9C ).

Rostrum directed anteriorly and clearly defined from dorsal cephalothoracic shield ( Fig. 9D ). Antennule ( Fig. 9E ) 180 µm long and 4-segmented; armature formula 3+spine, 10+spine, 6+2 aesthetascs, and 7+aesthetasc; spines on first and second segment short and spinulose; first segment with large patch of spinules on ventral surface; third segment with 5–8 scale-like processes on distal part of ventral surface. Antenna ( Fig. 9F ) 4-segmented; first segments (coxa-basis) smooth and unarmed; second segment (first endopodal segment) also unarmed but with 2 patches of spinules on medial side; third segment with 1 claw and 1 seta, and ornamented with 4 or 5 epicuticular scales (proximalmost scale directed distally and remaining scales directed proximally) in mediodistal region; terminal segment 23×11 µm (ratio 2.09:1), armed with 4 claws and 2 smooth setae on distal margin and ornamented with several small spinules on outer margin; 2 medial claws on terminal segments each with rows of fine spinules bilaterally; 2 outer claws each with 3 or 4 spinules on concave medial margin.

Labrum ( Fig. 9G ) with patch of spinules on each side and a pair of curved digitiform processes in middle of posterior margin. Mandible ( Fig. 10A ) with 1 large plumose seta distally (this seta transparent and easily detached) and 1 spiniform element with bifurcate apex and lateral membranous flange. Paragnath ( Fig. 10B ) a densely spinulose lobe with small process on posterior margin. Maxillule ( Fig. 10C ) lobate, with naked 5 setae. Maxilla ( Fig. 10D ) 2-segmented; proximal segment unarmed but with 1 pointed ventrodistal process; distal segment stout, distally curved giving claw-like appearance, densely covered with spinules and armed with 1 robust, spinulate spine on dorsal surface and 1 minute, tubercle-like, seta on ventral surface. Maxilliped ( Fig. 10E ) slender and 4- segmented; first and third segments unarmed; second segment with 2 naked setae in middle of medial margin; terminal segment armed with 2 setae, 1 spine and 1 spiniform process fused to segment, distal seta markedly longer than distal spine.

Legs 1–4 ( Fig. 10F–I ) biramous, with 2-segmented rami, all ornamented with patches of spinules on coxa, basis and outer surface of rami. Inner seta on coxa of legs 1–4 small and smooth; outer seta on basis of legs large and smooth. Posterior margin of basis of legs 1–4 each with 1 or 2 inner setules. Armature formula of legs 1–4 as follows:

Leg 1: coxa 0-1; basis 1-0; exp. I-0; II, 2, 4; enp. 0-0; 3

Leg 2: coxa 0-1; basis 1-0; exp. I-0; I, 2, 3; enp. 0-0; 4

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

Leg 4: coxa 0-1; basis 1-0; exp. I-0; 2, 3, 2; enp. 0-0; 0

Leg 5 ( Fig. 10J ) 2-segmented but proximal protopodal segment incorporated into somite, with 1 posterolateral seta; free distal segment (exopod) small, rectangular, wider than long, armed with 4 setae (1 small seta on medial margin, 1 large plus 2 small setae on distal margin). Leg 6 not seen.

Remarks. In all of four species of Rhodinicola observed in the present work ( R. gibbosus , R. rugosum , R. tenuis n. sp. and R. similis n. sp.), the mandible is armed distally with a large plumose seta plus either a spiniform process or an articulated element. The plumose seta is transparent and easily detached and, therefore, has probably gone unnoticed in previous descriptions of R. rugosum and R. gibbosus . The mandibles of R. elongata Levinsen, 1878 and R. thomassini Laubier, 1970 are in need of re-examination to check for the presence of this plumose seta. However, this characteristic form of mandible, as shared by the four species listed above, differs markedly from the mandible of R. laticauda Ho and Kim, 2003 and R. polydorae Björnberg & Radashevsky, 2011 , both of which have two spiniform elements, one distal and one subdistal ( Ho and Kim, 2003; Björnberg and Radashevsky, 2011). In addition, the maxilliped of female R. laticauda and R. polydorae , which is rudimentary, differs from the welldeveloped limbs present in females of all other Rhodinicola species. We anticipate that R. laticauda and R. polydorae may well have to be assigned to a new genus in a future revision of the family Clausiidae .

R. rugosum was originally described in 1895 associated with Praxilla sp. from Naples. Surprisingly there have been no records since, until its re-discovery by Sue Hamilton in the Irish Sea exactly 100 years later. It appears to be widely distributed around the British Isles on a range of maldanid hosts including Euclymene sp. , Praxillella affinis , Clymenura tricirrata and Clymenura johnstoni . One of the observed specimens was still attached to the skin of the host using its left and right maxillae together as pincers. It has also recently been observed on the west coat of Ireland in inner Galway Bay (pers. comm. Eddie McCormack, Aqua-Fact International Services Ltd, 2009). The Rhodinicola sp. copepodites found by Gotto & O’Connor (1980) in Galway Bay and by Capaccioni et al (1993) in the Ebro Delta (western Spain) probably belong to this species.

Figures

FIGURE 9. Rhodinicola rugosum (Giesbrecht, 1895), female. A, habitus, dorsal; B, habitus, lateral; C, posterior part of abdomen with caudal rami, ventral; D, rostral area, dorsal; E, antennule, ventral; F, antenna; G, labrum, ventral. Scales bars: A, B, 0.2 mm; C, 0.1 mm; D, E, 0.05 mm; F, G, 0.02 mm.

FIGURE 10. Rhodinicola rugosum (Giesbrecht, 1895), female. A, mandible; B, paragnath; C, maxillule; D, maxilla, dorsal; E, maxilliped; F, leg 1; G, leg 2; H, leg 3; I, leg 4; J, right leg 5, ventral; K, genital area. Scale bars: A–J, 0.02 mm; K, 0.05 mm.