Mesnilia cluthae, : Canu, 1898

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 : 12-15

Mesnilia cluthae (T. and A. Scott, 1896)

Clausia cluthae T. and A. Scott, 1896: 1, pl. 1, figs. 1–12; Wilson and Illg, 1955: 134.

Mesnilia cluthae: Canu, 1898: 402 ;

Mesnilia cluthae: Bocquet and Stock, 1959: 5 , figs. 1–5.

Mesnilia martinensis Canu, 1898: 401 , pls. VIII, IX. New synonym.

Material examined: 1 ♀ (dissected and figured) found among crushed Turritella shells in sample where two spionid species were present, Dipolydora socialis (Schmarda, 1861) and a smaller species; off Teignmouth, Devon, 3 km from mouth of River Teign, depth 15 m; collected by P. Garwood, 18 April 1990.

1 ♀ found loose in sample which included Clymenura tricirrata (Bellan & Reys, 1967) and other maldanid species; Central North Sea , Lundin Block 21-8, Stn 12 – F3 (57 o 40.3878’N, 00 o 24.2905’E), depth 104 m, found by S. Hamilton, April 2007; BMNH Reg. No. 2012.1375 .

1 ♀ collected from washings of littoral algae/ Sabellaria ; Dovercourt , Essex, England (51 o 53.3'N, 01 o 16.3'E), depth intertidal; collected by I. Killeen, found by R. Bamber, 08 March 1993; BMNH Reg. No. 2012.1375 .

Additional records. 1 ♀ from clump of Modiolus Lamarck, 1799 , Loch Creran , Scotland (56 o 32.76'N, 05 o 16.14'W), depth 15.5 m, collected by Scottish Natural Heritage / Sue Hamilton, 21 October 2005: deposited in National Museum of Scotland, NMSZ 2008.107 .2.

1 ♀ ovigerous, 1 ♂ from tube of Dipolydora flava, Sound of Harris , Scotland, Scottish Natural Heritage, Stn SA 105 (57 o 42.173'N, 07 o 00.390'W), depth 43 m; collected by Sue Hamilton, 10 November 2005: NMSZ 2008.107 .3.

1 ♀, 3 ♂ Stour Estuary, Suffolk, England, Unicomarine Stn 189a, collected by David Hall, 17 July 2008 .

1 ♀, Larne Lough , Northern Ireland, EHS Stn LL 2 (54 o 49.05'N, 05 o 45.35'W), depth 3 m; collected by Tim Mackie, 01 November 2008 .

1 ♀ Larne Lough , Northern Ireland, EHS Stn LLS2 (54 o 48.53'N, 05 o 44.37'W), depth 2.6 m; collected by Tim Mackie, 29 January 2009 .

1 ♀ Strangford Lough , Northern Ireland, EHS Stn Green Island (54 o 27.73'N, 05 o 36.64'W), depth 19.4 m; collected by Tim Mackie, 02 February 2009 .

1 ♀ in tube with complete Dipolydora flava , Shetland, Scotland, SEPA Stn Lerwick UWWTD B (60 o 12.60'N, 01 o 08.34'W), depth 45 m, found by Stephen Nowacki, 12 January 2012 .

Female. Body ( Fig. 5A ) elongate and dorsoventrally depressed, without prosome-urosome distinction. Body length 2.11 mm (body lengths of other 2 examined specimens 2.38 and 2.17 mm). Body somites distinct, demarcated by constrictions and arthrodial membranes between somites. Cephalothorax and succeeding 3 metasomal somites (second to fourth pedigerous somites) similar in width, 421×462, 185×456, 200×446, and 220×441 µm, respectively. Fifth pedigerous somite 200×364 µm. Genital and abdominal somites gradually narrowing from anterior to posterior. Genital somite 159×313 µm, relatively small; genital areas positioned dorsolaterally. Four free abdominal somites 205×281, 190×256, 144×226, and 179×179 µm, without ornamentation on ventral surface. Caudal rami divergent and distinctly separated from one another; each ramus ( Fig. 5B ) 108×47 µm (ratio 2.30:1) and armed with 6 smooth setae; mid-terminal seta distinctly larger than other 5 setae.

Rostrum ( Fig. 5C ) broad, with truncate anterior margin; suture line distinct between rostrum and dorsal cephalothoracic shield. Antennule ( Fig. 5D ) 229 µm long, 6-segmented, and gradually narrowing from proximal to distal; armature formula 4, 13(?), 10(?), 4, 2+aesthetasc, and 7+aesthetasc; all setae smooth; first segment with patch of spinules on proximal region of anterior surface. Antenna ( Fig. 5E ) 3-segmented; first segment with 1 seta mediodistally and patches of setules on distal half on medial side; second segment with 1 small seta on ventral surface and ornamented with patch of minute spinules on medial side; terminal segment (fused second and third endopodal segments) about twice as long as wide, armed with 1 claw, broad seta with flagellate tip and 1 small seta on medial margin, 4 claws of unequal size on distal margin, 2 weakly pinnate subdistal setae on outer margin, 1 patch of spinules on outer side and another patch of spinules on proximal half of medial margin.

Labrum ( Fig. 5F ) with prominent, tapering mid-terminal process on posterior margin and with membranous areas on each side of process; each membranous area with patch of setules. Mandible ( Fig. 5G ) with 2 spiniform elements; elongate distal element with 8 denticles distally, subdistal element shorter than distal, with spinules on posterior (outer) surface. Maxillule ( Fig. 5H ) lobate, densely covered with minute spinules on ventral surface and armed with 3 outer and 2 smaller inner setae. Maxilla ( Fig. 5I ) 2-segmented; proximal segment unarmed and smooth; distal segment truncate, with dense covering of minute spinules on distal surface and 2 setae near middle. Maxilliped ( Fig. 6A ) 3-segmented; first segment with 1 smooth seta mediodistally; second segment with 2 similar setae on medial margin; terminal segment blunt, with dense distal covering of minute spinules and 4 setae, 2 (one spiniform) located subdistally and 2 smaller setae located proximally.

Legs 1 and 2 ( Fig. 6B, C ) biramous with 3-segmented rami. Legs 3 and 4 ( Fig. 6D, E ) uniramous, with 3- segmented exopod, lacking endopod. Second exopodal segment of leg 3 armed with 1 outer spine and 1 inner seta (formula I-1) but occasionally inner seta lacking (formula I-0) (in one of 4 specimens). Both sides of intercoxal sclerite of legs 1 and 2 projecting (those of leg 1 more prominent), with patch of spinules ( Fig. 6B, C ). Outer margin of rami of legs 1–4 covered with spinules. Armature formula of legs 1–4 as follows:

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

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

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

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

Leg 5 ( Fig. 6F ) 2-segmented; proximal protopodal segment clearly defined from somite, with 1 dorsal seta; distal segment (exopod) 105×61 µm (ratio 1.72:1), distally with 4 setae and patches of minute spinules. Leg 6 not seen.

Remarks. T. and A. Scott (1896) recorded a single female in their original description of Mesnilia cluthae (as Clausia cluthae ) but they were in fact dealing with a male. The maxilliped (pl. 1, fig. 18) they illustrated is of male form and the morphology of the swimming legs is very different from that of female swimming legs described subsequently by Bocquet and Stock (1959). Similarities in the detailed structure of the male maxilliped and in the strong posterolateral projections on the intercoxal sclerite of leg 1 in both sexes serve to confirm that our specimen and the specimens of T. and A. Scott (1896) and Bocquet and Stock (1959) are conspecific.

Bocquet and Stock (1959) noted discrepancies between their male M. cluthae and that described by T. and A. Scott which they attributed to errors on the part of the latter authors. The rudimentary endopods on legs 3 and 4, observed by T. and A. Scott were not seen by Bocquet and Stock or in any of the present material. A very similar species Mesnilia martinensis Canu, 1898 was described from the Channel coast of France (near Cherbourg). Canu (1898) was aware of the similarities between M. cluthae and M. martinensis but only had female material available and did not consider that they might be male and female of the same species. Bocquet and Stock (1959) maintained M. martinensis as a separate species based on a number of minor differences in the antennae and mouthparts. It seems much more likely that these differences are simply descriptive inaccuracies by Canu and the two species are treated here as synonymous. The genus Mesnilia becomes monotypic, comprising only M. cluthae . Specimens examined subsequently by Gotto (1965) from Plymouth, and by Hamond (1973) from Norfolk are consistent with the redescription of Bocquet and Stock (1959). It is now evident that M.cluthae is widely distributed around the coast of the British Isles as well as the Channel coast of France.

Genera of the family Clausiidae have typically been distinguished mainly by leg morphology. It is notable that the morphology of cephalic appendages such as the antenna and mandible in M. cluthae is very close to that of Clausia lubbockii redescribed above, even though they have different leg morphologies.

Figures

FIGURE 5. Mesnilia cluthae (T. and A. Scott, 1896), female. A, habitus, dorsal; B, left caudal ramus, dorsal; C, rostrum, dorsal; D, antennule (open circles indicating insertion scars of missing setae); E, antenna; F, labrum, ventral; G, mandible; H, maxillule, medial; I, maxilla, posterior. Scale bars: A, 0.2 mm; B–E, 0.05 mm; F–I, 0.02 mm.

FIGURE 6. Mesnilia cluthae (T. and A. Scott, 1896), female. A, maxilliped; B, leg 1; C, leg 2; D, leg 3; E, leg 4; F, leg 5. Scale bars: A, 0.02 mm; B–E, 0.05 mm; F, 0.1 mm.