Melinnacheres terebellidis ( Levinsen, 1878 )

Boxshall, Geoff A., O’Reilly, Myles, Sikorski, Andrey & Summerfield, Rebecca, 2019, Mesoparasitic copepods (Copepoda: Cyclopoida) associated with polychaete worms in European seas, Zootaxa 4579 (1), pp. 1-69 : 39-42

Melinnacheres terebellidis ( Levinsen, 1878)

Syn: Saccopsis terebellidis Levinsen, 1878

Norwegian material examined: 1♀ from Terebellides stroemi -complex, TOGI, Stn 10-4 (60.57633°N, 03.65566°E), depth 304 m, 10 May 1998; collected by A. Sikorski. 1♀ from T. stroemi -complex, Sygna, Stn 5-2 (61.4645°N, 1.98727°E), depth 296 m, 11 June 1999; collected by A. Sikorski. 2♀♀ from T. stroemi -complex, Statfjord A, Stn 9-5 (61.26239°N, 01.839069°E), depth 147 m, 15 June 1999; collected by A. Sikorski. 1♀ from T. stroemi -complex, Gullfaks Satelitter, Stn GFK 3-4 (61.12791°N, 02.023441°E), depth 138 m, 18 June 1999; collected by A. Sikorski. 1♀ from Terebellides sp., Gullfaks Satelitter, Stn GFK 2-5 (61.0518°N, 02.078563°E), depth 134 m, 21 June 1999; collected by A. Sikorski. 1♀ from T. stroemi -complex, Gullfaks Satelitter, Stn GFH1-3 (61.05359°N, 02.075616°E), depth 134 m, 21 June 1999; collected by A. Sikorski. 1♀ from Terebellides sp., Vigdis, Stn 3-2 (61.39485°N, 02.072259°E), depth 278 m, 31 May 1999; collected by A. Sikorski. 2♀♀ from T. stroemi -complex, Oseberg East, Stn 3-4 (60.70634°N, 02.946468°E), depth 164 m, 23 May 2000; collected by A. Sikorski. 1♀ from T. stroemi -complex, Oseberg East, Stn 2-2 (60.70316°N, 02.939989°E), depth 161 m, 24 May 2000; collected by A. Sikorski. 1♀ from T. stroemi -complex, Oseberg East, Stn 6-1 (60.69365°N, 02.92649°E), depth 159 m, 24 May 2000; collected by A. Sikorski. 1♀ from T. stroemi -complex, Glitne, Stn 2-5 (58.71169°N, 01.667961°E), depth = 105 m, 30 May 2000; collected by A. Sikorski. 1♀ from T. stroemi -complex, Balder, Stn 46- 5 (59.19403°N, 02.351991°E), depth 123 m, 0 1 June 2000; collected by A. Sikorski. 1♀ from T. stroemi -complex, Jotun, Stn 13-1 (59.4489°N, 2.362146°E), depth = 115 m, 0 5 June 2000; collected by A. Sikorski. 1♀ from T. stroemi -complex, Troll B, Stn 50-4 (60.7272°N, 03.157842°E), depth 321 m, 26 May 2001; collected by A. Sikorski. 2♀♀ from 2 specimens of T. stroemi -complex, TOGI, Stn 9-3 and 4 (60.5739°N, 03.6194°E), depth 301 m, 28 May 2001; collected by A. Sikorski. 1♀ from T. stroemi -complex, R/V “ Jan Mayen ”, Duvefjorden, Stn 1121-4 (80.2285°N, 23.21783°E), depth 112 m, 19 September 2001; collected by A. Sikorski. 1♀ from T. stroemi - complex, Alfa Nord, Stn A5, 1-3 (58° 29.799’N, 01° 43.422’E), depth 108 m, 4–11 September 2003; collected by A. Sikorski. 1♀ from T. stroemi -complex, Alfa Nord, Stn A5, 0-4 (58° 29.799’N, 01° 43.611’E), depth 108 m, 4–11 September 2003; collected by A. Sikorski. 2♀♀ from 2 specimens of T. stroemi -complex, Alfa Nord, Stn A1, 0-3 (58° 29.946’N, 01° 43.422’E), depth 108 m, 4–11 September 2003; collected by A. Sikorski. 1♀ from T. stroemi - complex, Alfa Nord, Stn A11, 1 (58° 29.835’N, 01° 43.118’E), depth 108 m, 4–11 September 2003; collected by A. Sikorski. 1♀ from T. stroemi -complex, Alfa Nord, Stn Ref, (58° 29.300’N, 01° 43.361’E), depth 108 m, 4–11 September 2003; collected by A. Sikorski. 9♀♀ from 3 specimens of T. stroemi -complex, Alfa Nord, Stn A8, 0-4 (approx. 58° 29’N, 091° 53’E), depth 108 m, 4–11 September 2003; collected by A. Sikorski. 4♀♀ from 3 specimens of T. stroemi -complex, SVAN, Stn 1bio-1, 8bio-2 & 3 (approx. 58° 29’N, 091° 53’E), depth 108 m, 4–11 September 2003; collected by A. Sikorski. 1♀ from T. stroemi -complex, Finnmark, Stn 592-C (70.065°N, 29.0663°E), depth 88 m, 13 September 2003; collected by A. Sikorski. 2♀♀ from 2 specimens of T. stroemi - complex, SVAN, Stn ALF 2 (58.50145°N, 01.7242°E), depth 108 m, 20 April 2004; collected by A. Sikorski. 2♀♀ from 2 specimens of T. stroemi -complex, SVAN, Stn ALF 1-3 (58.49923°N, 01.723466°E), depth 108 m, 20 April 2004; collected by A. Sikorski. 3♀♀ from 3 specimens of T. stroemi -complex, SVAN, Stn ALF 17 (58.4986°N, 01.7242°E), depth 108 m, 20 April 2004; collected by A. Sikorski. 2♀♀ from T. stroemi -complex, Oseberg Øst, Stn 7-3 (60.6873°N, 02.960°E), depth 155 m, 21 May 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, Oseberg Øst, Stn 16-2 (60.6746°N, 02.986°E), depth 157 m, 24 May 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, Oseberg Øst, Stn 3-1 (60.7069°N, 02.9459°E), depth 158 m, 24 May 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, Brage, Stn 10-2 (60.531°N, 03.06337°E), depth 133 m, 27 May 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, TOGI, Stn 10-5 (60.5743°N, 03.654°E), depth 300 m, 0 1 June 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, TOGI, Stn 11R-4 (60.5727°N, 03.8383°E), depth 298 m, 0 1 June 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, Troll B, Stn 8-5 (60.7508°N, 03.4456°E), depth 325 m, 0 2 June 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, Troll C, Stn 1-2 (60.8942°N, 03.582°E), depth 347 m, 0 3 June 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, Troll C, Stn 8-5 (60.8942°N, 03.6765°E), depth 340 m, 0 3 June 2004; collected by A. Sikorski. 3♀♀ from T. stroemi - complex, Troll C, Stn 99r-G (61.02043°N, 03.4643°E), depth 350 m, 0 4 June 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, Stj Sund, Stn 12-1 (70.279°N, 23.40095°E), depth 401 m, 17 September 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, Barents Sea, Hopen Bank, Stn 12-2 (75° 55.1’N, 25° 19.2’E), depth 111 m, 24 May 2005; collected by A. Sikorski. 1♀ from T. stroemi -complex, Visund Nord, Stn 5-1 (61.4295°N, 02.557536°E), depth 380 m, 0 6 June 2005; collected by A. Sikorski. 2♀♀ from T. stroemi -complex, Vigdis F, Stn 2-5 (61.32626°N, 02.078652°E), depth 235 m, 13 June 2005; collected by A. Sikorski. 1♀ from T. stroemi - complex, Narvik, Stn 10-2 (68.43667°N, 17.34583°E), depth 159 m, 0 4 July 2005; collected by A. Sikorski. 1♀ from T. stroemi -complex, Resi Stagnes, Stn 7-3 (68° 45.498’N, 16° 35.701’E), depth 93 m, 28 June 2006; collected by A. Sikorski. 1♀ from T. stroemi -complex, Vega, Stn 3-2 (65.69202°N, 12.131583°E), depth 130 m, 0 4 December 2006; collected by A. Sikorski. 1♀ from T. stroemi -complex, FFH 3958, Stn B3 (65.9283°N, 12.25177°E), depth 105 m, 23 March 2007; collected by A. Sikorski. 1♀ from T. stroemi -complex, Nessar, Hopen Bank Stn 20-5 (76° 22.65’N, 27° 38.19’E), depth 109 m, 2007; collected by A. Sikorski. 3♀♀ from 3 specimens of T. stroemi -complex, 4475 Eidsfjord, Stn DYP1-1 (68.6987°N, 15.03037°E), depth 159 m, 0 7 October 2008; collected by A. Sikorski. 4♀♀ from 4 specimens of T. stroemi -complex, 4475 Eidsfjord, Stn DYP2-1 (68.7092°N, 15.05468°E), depth 147 m, 0 7 October 2008; collected by A. Sikorski. 1♀ from T. stroemi -complex, 4391 Vannområder Rana, Stn 86S (66.21793°N, 13.59785°E), depth 86 m, 15 October 2008; collected by A. Sikorski. 2♀♀ from 2 specimens of T. stroemi -complex, Narvik Kom, Stn T2, 2-4 (68.45588°N, 17.43487°E), depth 334 m, 19 July 2009; collected by A. Sikorski. 2♀♀ from 2 specimens of T. stroemi -complex, 3566 Nessar, Stn G-12-5 (75° 55.23’N, 25° 19.42’E), depth 109 m, 0 1 October 2009; collected by A. Sikorski. 5♀♀ from 5 specimens of T. stroemi -complex, Tysfjord, Stn T3 (67° 53.776’N, 16° 13.393’E), depth 166 m, 14 October 2009; collected by A. Sikorski. 5♀♀ from 4 specimens of T. stroemi -complex, Mørsvikbotn 2010, Stn Mø 3-1 (67.69995°N, 15.82092°E), depth 157 m, 16 June 2010; collected by A. Sikorski. 2♀♀ from 2 specimens of T. stroemi -complex, Digermulen, Stn S3-A (66.67955°N, 12.34188°E), depth 210 m, 25 November 2010; collected by A. Sikorski. 1♀ from T. stroemi -complex, Nord Fugløya, Stn S2-A (67.08334°N, 13.86458°E), depth 100 m, 31 March 2011; collected by A. Sikorski. 1♀ from T. stroemi -complex, Mareano 2012106, Stn 844, sample 101, depth unknown, 10 May 2012; collected by A. Sikorski. 1♀ from T. stroemi -complex, 5796 Garn Vest, Stn GAW 02-2 (64.34634°N, 07.728725°E), depth 263 m, 12 June 2012; collected by A. Sikorski. 1♀ from T. stroemi -complex, 6489 Suncor, Stn S2 MFB (61.64353°N, 02.09707°E), depth 375 m, 24 July 2013; collected by A. Sikorski. 1♀ from T. stroemi - complex, 6987 Linesvika, Stn 3A (66.54667°N, 13.32928°E), depth 319 m, 24 March 2014; collected by A. Sikorski. 1♀ from T. stroemi -complex, 7178 Kornstad C, Stn 5-3 (62.95308°N, 07.459533°E), depth 181 m, 16 June 2014; collected by A. Sikorski. 1♀ from T. stroemi -complex, 7288 Lerøy Vest 2014, Stn Ap3 (60.00465°N, 05.3126°E), depth 350 m, 16 June 2014; collected by A. Sikorski. 1♀ from T. stroemi -complex, 7299 Ånholmen, Stn Ånh 2-1 (64.72338°N, 11.44812°E), depth 256 m, 13 August 2014; collected by A. Sikorski. 2♀♀ from T. stroemi -complex, 7884 Salasbruket 2015, Stn SAL 3-1 (64.79697°N, 11.83655°E), depth 51 m, 24 August 2015; collected by A. Sikorski. 1♀ from T. stroemi -complex, 7886 Daljorda, Stn Da 3-2 (68.68988°N, 14.96113°E), depth 181 m, 24 September 2015; collected by A. Sikorski. 1♀ from T. stroemi -complex, 8190 Hammer ASC, Stn C2-2 (67.96502°N, 15.1663°E), depth 108 m, 31 March 2016; collected by A. Sikorski. NHMUK Reg. Nos 2016.563- 572. 1 mature ♀ with 3 ♂♂ on gill stalk of T.shetlandica , ( APEM), site KVE1-2 Solund (61° 00.025’N, 04° 44.803’E), depth 66 m, 13 June 2017. 1 ovigerous ♀ with 3 ♂♂ on dorsum of T. shetlandica , ( APEM), site JOR2- 2 Finnoy (59° 17.907’N, 05° 56.325’E), depth 366 m, 0 1 June 2017 .

British material examined: 5♀♀ from 3 specimens of T. stroemi -complex, northern North Sea (near Faeroes), UKCS 210 /29, Stn 68-9678, depth 160 m, collection date unknown; collected by R. Bamber. 1 ovigerous ♀ with 2 ♂♂ detached from host, APEM project, North Sea , location UKCS 13 /24 Bagpuss, ENV1-B collection data unknown. 1 ovigerous ♀ on “host”, APEM project 413646, location UKCS 9 /13 Beryl, A 9-MFA, location UKCS 9 /13 Beryl collection data unknown. 1 mature ♀ on “host”, APEM project 413646, location UKCS 9 /13 Beryl , B8- MFA, collection data unknown. 1 ovigerous ♀ from “host”, ( APEM), North Sea , location GG1-FA (57° 13.5512’N, 01° 59.6894’E), depth 96 m, 0 4 August 2018; collected by Fugro EMU Ltd. 1 immature ♀ from “host”, ( APEM), North Sea , location GG2-FA (57° 13.0762’N, 01° 58.9468’E), depth 94 m, 0 4 July 2013; collected by Fugro EMU Ltd. 1 ovigerous ♀, 3 immature ♀♀ from 2 specimens of T. shetlandica CNS 72, collection data unknown. collected by P. R. Garwood. 3 ovigerous ♀♀ from 3 specimens of T. shetlandica , RMA CORDAH locality data unknown, 11 December 2003; collected by P. R. Garwood. 1 ovigerous ♀ on T. shetlandica ( APEM), Stn GBRCUGR_14, Curlew Field, North Sea (56° 44.205’N, 01° 36.690’E), depth 98 m, 23 July 2016; collected by Fugro EMU Ltd. 1 ovigerous ♀ on T. shetlandica , ( APEM), Stn GBRCUGR_24, Curlew Field, North Sea (56° 43.164’N, 01° 41.426’E), depth 93 m, 22 July 2016; collected by Fugro EMU Ltd. NHMUK Reg. Nos 2018.163- 172 .

Differential diagnosis. Female ectosoma dorso-ventrally flattened, tapering towards anterior end from maximum width located near posterior end ( Fig. 15E, F ), ectosoma about 2.07 times longer than maximum width (range 1.6 to 2.69 times longer); mean ectosoma length 1.41 mm, with range of 0.88 to 2.07 mm (based on 10 ovigerous specimens), mean greatest width 0.69 mm (range 0.44 to 1.12 mm), mean depth 0.55 mm (range 0.31 to 0.92 mm). Genital apertures carried on small swellings on posterior margin, separated by distinct gap greater than width of each swelling. Paired cement glands curved, extending only over about posterior 25% of ectosoma length Fig. 15E, F ). Egg sacs multiseriate ( Fig. 15G ); varying from slightly curved to loose spiral in form; typically about 1.1 times longer than ectosoma, varying from shorter than to 1.5 times longer than ectosoma; mean length 1.62 mm (range 0.86 to 2.90 mm).

Remarks. Levinsen (1878) based his description of M. terebellidis on a single adult female from Greenland, and this species was commonly confused with M. steenstrupi prior to the careful documentation of the differences between them by Bresciani & Lützen (1961) which led to the establishment of the latter. Bresciani & Lützen (1961) considered that the most reliable characters for identifying the adult female of M. terebellidis are its relatively large body size, up to 4.0 mm, and the limited extent of the cement glands which extend over only about the posterior quarter of the ectosoma, as figured by Levinsen (1878). After examination of large samples of both M. terebellidis and M. steenstrupi , we found that ectosoma shape is the most useful character. All the M. terebellidis found on their hosts by O’Reilly (2016) were attached to the anterior dorsum whereas the M. steenstrupi were attached to the gill or the gill stalk. One of the Norwegian specimens of M. terebellidis found here (penultimate specimen cited above) was found on the gill stalk of its host. This seems to be an unusual location for this parasite, although Levinsen (1978) in the type description did highlight a juvenile female attached to the host gill.

The body size cited by Bresciani & Lützen (1961) for M. terebellidis was up to 4.00 mm, whereas the largest specimen in our collection that exhibited this tapering, flattened ectosoma shape was 2.07 mm. O’Reilly (2016) reported an average length of 1.1 mm (range 0.61 to 1.60 mm) for a large sample of ovigerous females of M. terebellidis taken mostly from the northern North Sea, but including some from the southern North Sea, Celtic Sea and from Kosterfjord ( Sweden). The largest specimen he recorded from Scottish waters was 1.6 mm in length and carried egg sacs 2.2 mm long. The mean and range of ectosoma sizes exhibited by the ovigerous females in our materal is very similar to that reported by O’Reilly, although the maximum size (2.07 mm long and with egg sacs 2.9 mm) was longer. The size variation is very marked and it is possible that this is indicative of cryptic taxonomic diversity.

The polychaete Terebellides stroemi was originally recorded as the host of both M. terebellidis and M. steenstrupi , but T. stroemi has recently been shown to be a species complex ( Parapar et al. 2011, 2016). O’Reilly (2016) reported Terebellides shetlandica Parapar, Moreira & O’Reilly, 2015 as host of M. terebellidis in British and Swedish waters. Above we reported the discovery of M. streenstrupi on T. atlantis , as well as on T. stroemi - complex. A recent investigation of the genetics of Terebellides in the North East Atlantic ( Nygren et al. 2018) indicated that more than 25 species occur in the area, of which only seven have been formally described. Future studies may reveal comparable diversity within the parasitic copepods that exploit these polychaetes, but molecular evidence will undoubtedly be needed to support the very limited morphological evidence available from these highly modified and reduced parasites.

The male of M. terebellidis was briefly described by O’Reilly (2016) who noted that it was similar to that of M. steenstrupi as described by Bresciani & Lützen (1961). The male described by O’Reilly (2016) had a body length of about 140 µm, slightly smaller than the male described here for M. ergasiloides .

Figures

FIGURE 15. Melinnacheres steenstrupi Bresciani & Lützen, 1961. A, ovigerous female, dorsal; B, same, ventral; C, same, lateral; D, detached egg sac. Melinnacheres terebellidis Levinsen, 1878. E, ovigerous female, dorsal; F, same ventral; G, detached egg sac. All scale bars 1 mm.