Sheaderia bifida, 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 : 38-41

Sheaderia bifida n. gen. et n. sp.

Type material: Holotype ♀ (dissected and mounted on a glass slide) from unknown host; St. Magnus Bay , Shetland (60º 23.44’N, 01º 33.84’W), depth 146 m, collected by S. Hamilton, 04 May 1993; BMNH Reg. No. 2012.1385.

Paratype ♀ (dissected and mounted on a glass slide) from the maldanid Euclymene oerstedii , northern North Sea , no other locality data, collected by M. Sheader; BMNH Reg. No. 2012.1392 .

Paratype ♀ found loose in sample containing Clymenura tricirrata and other maldanid species; central North Sea , Lundin Block 21-8, Stn 6 – F1 (57 o 40.8664’N, 00 o 25.0638’E), depth 104 m, April 2007; BMNH Reg. No. 2012.1393 .

Female. Body ( Fig. 21A ) elongate, with well-defined somites. Body length 1.88 mm, excluding caudal setae. Prosome consisting of cephalothorax and second to fifth pedigerous somites. Urosome consisting of genital complex and 2-segmented abdomen ( Fig. 21B ). Cephalothorax tapering anteriorly and 472×494 µm, with ventrolaterally folded margins to dorsal cephalothoracic shield ( Fig. 21D ), and rounded frontal margin and posterolateral corners. Second to fifth pedigerous somites well-delimited, with convex lateral margins. Fifth pedigerous somite only slightly narrower than preceding somite and 438 µm wide. Genital complex 157×273 µm, with convex lateral margins; genital areas located ventrally but hardly discernible. First abdominal somite very short, about one-fifth as long as anal somite. Anal somite 200×169 µm and unornamented. Caudal ramus ( Fig. 21C ) slender, tapering and 212×52 µm (ratio 4.08:1), with 1 lateral and 3 distal setae.

Rostrum with truncate posterior margin ( Fig. 21D ). Antennule ( Fig. 21E ) small, 5-segmented, gradually narrowing from proximal to distal; armature formula 3, 8, 4+aesthetasc, 2+aesthetasc, and 4+aesthetasc; all setae naked and short. Antenna ( Fig. 21F ) 4-segmented; first segment smooth and unarmed; second segment with 1 small seta and patch of large spinules mediodistally; third segment with 3 distal claws (two of them small) and ornamented with numerous large spinules on medial surface; terminal segment as long as wide, much smaller than proximal segments and armed with 4 claws.

Labrum ( Fig. 21G ) comprising small ventral and large dorsal plates; both plates strongly tapering distally. Mandible ( Fig. 21H ) with 1 large, tapering distal blade articulated at base, with membranous flange along distal part of medial (anterior) margin. Maxillule ( Fig. 21I ) lobate, distally with 2 small inner and 2 large outer setae. Maxilla ( Fig. 22A ) 2-segmented; large proximal segment unarmed; stout distal segment wider than long, with 2 thick setae near middle and ornamented with numerous spinules on distal surface. Maxilliped ( Fig. 22B ) stout and 3-segmented; first segment much wider than long and unarmed; second segment broader than long, with 2 small setae on medial margin; third segment with 1 small lateral seta and dense spinules on distal surface.

Legs 1 and 2 ( Fig. 22C, D ) with broad coxa and basis, and stocky 2-segmented rami, bearing dense covering of spinules on outer surfaces. Leg 3 ( Fig. 22E ) lobate and tipped with 1 naked seta. Leg 4 absent. Armature formula of legs 1 and 2 as follows:

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

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

Leg 5 ( Fig. 22F ) 2-segmented; proximal segment large but unarmed; distal segment slightly narrowing distally, 92×53 µm (ratio 1.74:1), with 1 small subdistal and 2 distal setae, and ornamented with distal patch of spinules. Leg 6 not discernible.

Male. Unknown.

Etymology. The specific name bifida is derived from the Latin bifidus, meaning “split into two parts”. It refers to the possession of the double plates of the labrum and the two-segmented abdomen.

Remarks. The undissected paratype female from the central North Sea (BMNH 2012.1393) has a single distal seta on the left leg 3 and two distal setae on the right leg 3. This specimen also has a small papilla-like, unarmed leg 4. However, no other significant difference from the holotype was noted.

Figures

FIGURE 21. Sheaderia bifida n. gen. et n. sp., female. A, habitus, dorsal; B, urosome, ventral; C, right caudal ramus, dorsal; D, anterior part of cephalothorax, ventral view showing limbs in situ; E, antennule; F, antenna; G, labrum, ventral; H, mandible; I, maxillule. Scale bars: A, 0.2 mm; B–D, 0.1 mm; E–I, 0.02 mm.

FIGURE 22. Sheaderia bifida n. gen. et n. sp., female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 3; F, leg 5. Scale bars: A–E, 0.2 mm; F, 0.05 mm.