Rhodinicola tenuis, Kim & Sikorski & O’Reilly & Boxshall, 2013

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 : 23-26

Rhodinicola tenuis n. sp.

Type material: Holotype ♀ (dissected and mounted on a glass slide) from unknown host; R / V Smolensk, Stn 25-3 (70°08.0’N, 56°58.5’E), depth 69 m, 15 August 2004; BMNH Reg. No. 2012.1382.

Female. Body ( Fig. 11A ) slender, elongate, and composed of cephalothorax, unsegmented trunk and 4- segmented abdomen. Body length 5.15 mm, excluding caudal setae. Cephalothorax 770×640 µm, slightly expanded posterolaterally, not articulated from trunk but clearly defined from it by prominent lateral constriction. Trunk incorporating second to fifth pedigerous somites and genital somite, narrower than cephalothorax, and gradually narrowing from anterior to posterior, with paired lateral expansions at level of insertions of legs 2–5. Area of genital somite expanded laterally, 570 µm wide across this area; paired genital apertures located ventrolaterally ( Fig. 11B ). Abdomen small: four free abdominal somites 192×269, 123×246, 92×200, and 192×208 µm, respectively. Caudal ramus ( Fig. 11C ) rectangular, 119×62 µm (ratio 1.92:1), with 7 naked setae, distal seta much larger than others.

Rostrum as rounded ventral protuberance ( Fig. 11D ). Antennule ( Fig. 11D ) 257 µm long and 6-segmented; armature formula 4, 9, 5, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; second seta of first segment weakly pinnate; distalmost seta of this segment thick and plumose ( Fig. 11D ). Antenna ( Fig. 11E ) 4-segmented; first segment with 1 distal pinnate seta; second segment with 1 small subdistal seta; third segment with 1 claw and 1 seta distally and with longitudinal row of 6 foliaceous scales ornamenting segment; terminal segment 36×21 µm (ratio 1.71:1), bearing 4 claws and 2 long pinnate setae.

Labrum ( Fig. 11F ) with roundly convex posterior margin and ornamented with patches of minute spinules. Mandible ( Fig. 11G ) terminating in 1 or 2 cusps distally and carrying on distal margin 1 large plumose seta and 1 rounded hyaline element terminating in 2 small points. Maxillule ( Fig. 11H ) with 1 minute lateral, 1 subdistal and 3 distal setae. Maxilla ( Fig. 11I ) 2-segmented; proximal segment unarmed; distal segment with slightly recurved and pointed apex, armed with 1 minute seta and 1 dentiform process on concave margin and spinulose pad on slightly curved distal margin. Maxilliped ( Fig. 11J ) 3-segmented; first segment with 1 distal seta on medial margin; second segment with 1 seta in distal third of medial margin; third segment tapering into spiniform distal process with 2 setae and 1 small spine.

Legs 1–4 ( Fig. 12A–D ) biramous with 3-segmented rami; basis ornamented with 2 patches of spinules in leg 1 and 1 patch in legs 2–4. All segments of both rami of all legs with spinulose outer margins. Inner seta on coxa of legs 1–4 small and pinnate, outer seta on basis, large and naked. All setae on rami of legs 1–4 naked proximally and weakly pinnate distally. Armature formula of legs 1–4 as follows:

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

Leg 2: coxa 0-1; basis 1-0; exp. I-0; I-1; II, II, 4 (or II, I, 5); enp. 0-1; 0-2; I, II, 3

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

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

Leg 5 ( Fig. 12E ) 2-segmented; proximal segment fused with somite, with 1 outer seta; free distal segment (exopod) 82×32 µm (ratio 2.56:1), with 1 outer and 2 distal setae. Leg 6 represented by 2 minute spinules in genital area ( Fig. 11B ).

Male. Unknown.

Etymology. The specific name tenuis , meaning “slender” in Latin, alludes to the slender body of the new species.

Remarks. The new species belongs in the genus Rhodinicola because it has three-segmented rami of legs 1–4 and no posteromedian element on the basis of leg 1. The ventral location of leg 5 on its somite is also a feature of Rhodinicola , as Boxshall and Halsey (2004) considered it a key character of that genus. The species R. laticauda and R. polydorae both have a laterally located leg 5, unlike typical Rhodinicola species , futher highlighting the need for the affinities of these species to be reassessed. Within the genus Rhodinicola , the new species is most closely related to R. elongata (as redescribed by Bresciani, 1964a). They share a number of characteristics such as the 6-segmented antennules, the 4-segmented abdomen and antenna, the 3-segmented maxilliped, and the similar shape of the maxilla.

According to the Bresciani’s redescription and illustrations, R. elongata has, unlike R. tenuis n. sp., two lanceolate spines and three setae on the first antennular segment, only one element on the third antennary segment, a simple mandible bearing only one spiniform distal element, nine or ten elements (having ten is certainly abnormal) on the third exopodal segment of leg 2, and a more slender free exopodal segment of leg 5. These features of R. elongata differentiate it from R. tenuis n. sp. It should be noted that Fig. 1F of Bresciani (1964a), that was labeled leg 1, is in fact leg 4.

Figures

FIGURE 1. Anomoclausia indrehusae Gotto, 1964, female. A, habitus, dorsal; B, habitus, lateral; C, urosome, dorsal; D, left side of genital double and first abdominal somites, dorsal; E, left caudal ramus, dorsal; F, egg sac; G, antennule; H, antenna. Scale bars: A, B, 0.2 mm; C, F, 0.1 mm; D, 0.05 mm; E, G, H, 0.02 mm.

FIGURE 11. Rhodinicola tenuis n. sp., female. A, habitus, dorsal; B, urosome, ventral; C, left caudal ramus, ventral; D, rostrum and antennule, dorsal; E, antenna; F, labrum, ventral; G, mandible; H, maxillule; I, maxilla; J, maxilliped. Scale bars: A, 0.5 mm; B, 0.2 mm; C–J, 0.05 mm.

FIGURE 12. Rhodinicola tenuis n. sp., female. A, leg 1; B, leg 2; C, leg 3; D, leg 4; E, leg 5. All scale bars: 0.05 mm.