Melinnacheres steenstrupi ( Bresciani & Lützen, 1961 )

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 : 37-39

Melinnacheres steenstrupi ( Bresciani & Lützen, 1961)

Syn: Saccopsis steenstrupi Bresciani & Lützen, 1961

Norwegian material examined: 1♀ from Terebellides stroemi -complex, Ba-1992, Slope between Spitsbergen Bank and Hopen Trough, Stn 14-3 (75° 22.0’N, 26° 37.0’E), depth 189 m, 0 9 August 1992; collected by A. Sikorski. 1♀ from T. stroemi -complex, Glitne , Stn 6-5 (58.71169°N, 01.675149°E), depth = 105 m, 30 May 2000; collected by A. Sikorski. 1♀ from T. stroemi -complex, R/V “ Jan Mayen ”, Hinlopen , Stn 1137-1 (79.67333°N, 18.62767°E), depth 267 m, 21 September 2001; collected by A. Sikorski. 1♀ from T. stroemi -complex, Alfa Nord , Stn A-1, 0-3 (58° 29.946’N, 01° 43.422’E), depth 108 m, 0 4 – 11 September 2003; collected by A. Sikorski. 1♀ from T. stroemi -complex, SVAN, Stn ALF 3 (58.5059°N, 01.7591°E), depth 108 m, 20 April 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 18-5 (60.7127°N, 02.9082°E), depth 152 m, 25 May 2004; collected by A. Sikorski. 4♀♀ from 3 specimens of T. stroemi -complex, Troll B, Stn 10-1 (60.7112°N, 03.5105°E), depth 314 m, 0 2 June 2004; collected by A. Sikorski. 1♀ from T. stroemi -complex, Barents Sea , Hopen Bank Stn 12-5 (75° 55.1’N, 25° 19.2’E), depth 111 m, 24 May 2005; collected by A. Sikorski. 1♀ juvenile from T. stroemi -complex, Nucula , Stn 2-3 (71.55047°N, 25.23236°E), depth 292 m, 0 5 September 2006; collected by A. Sikorski. 2♀♀ juveniles from Terebellides stroemi -complex, Nessar , Hopen Bank slope Stn G-14 (75° 21.94’N, 26° 37.12’E), depth 191 m, 16 August 2007; collected by A. Sikorski. 2♀♀ from 2 specimens of T. stroemi -complex, Nessar , Stn G-12 (75° 55.12N, 25° 20.88’E), depth 111 m, 29 April 2008; collected by A. Sikorski. 2♀♀ juveniles from T. stroemi -complex, Kristin , Stn Q5-5 (64.85565°N, 06.451107°E), depth 330 m, 0 6 June 2009; collected by A. Sikorski. 6♀♀ from 2 specimens of T. stroemi -complex, Codfarmers , Mørkvedbukta, Stn Dyp 1-2 (67° 16.591’N, 14° 33.314’E), depth 32 m, 15 July 2009; collected by A. Sikorski. 1♀ from T. stroemi - complex, Mareano 2010110, Stn 531, sample 389 (70° 42.0081’N, 18° 33.3673’E), depth 372 m, 31 July 2010; collected by A. Sikorski. 1♀ from T. stroemi -complex, Niva 2014, Stn 525 - G, sample B05- IIIE (58.3252°N, 08.6295°E), depth 52 m, 0 2 March 2013; 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. NHMUK Reg. Nos 2016.553-562 . 5♀♀ from 2 specimens of Terebellides atlantis Williams, 1984 , 5796 Yttergryta 2012, Stn YTG7-4 (65.10969°N, 07.512037°E), depth 302 m, 29 May 2012; collected by A. Sikorski. 1♀ from T. atlantis , 5463 Stjernsund , Stn 12-3 (70.27983°N, 22.4015°E), depth 402 m, 15 August 2012; collected by A. Sikorski ; NHMUK Reg. Nos 2016.521-526 .

British materal examined: 1 ovigerous ♀, 1 mature ♀ from gill of T. stroemi , Shetland BGI, depth unknown, 2002; collected by P. R. Garwood. 1 mature ♀ from gill of T. stroemi , Shetland BGIN S5 OA, depth unknown, 2003 ; collected by P. R. Garwood. 5 ovigerous ♀♀ from single specimen of T. stroemi , Shetland, Flotta Stn N50B, depth unknown, 2003 ; collected by P. R. Garwood; NHMUK Reg. Nos 2017.487-490. 7 mature and juvenile ♀♀ on gills of T. stroemi, Skye, Loch Greshornish , depth unknown, 0 7 July 2004 ; collected by P. R. Garwood. 2 ovigerous ♀♀ from single T. stroemi, Cole Deep , depth unknown, 2004; collected by P. R. Garwood. 1 ovigerous ♀ from gill of T. stroemi , Belfast Lough, North Channel, EHS Stn CON/ Muck Isle C, (54° 50.5101’N, 05° 42.8499’W), depth 16 m, collected 14 March 2013 by Tim Mackie. NHMUK Reg. Nos 2018.153-162 .

Differential diagnosis. Adult female body ovoid ( Fig. 15A ) and lacking externally expressed segmentation: mean ectosoma length 1.18 mm, with range of 0.57 to 1.94 mm (based on 10 ovigerous specimens), mean width 0.92 mm (range 0.55 to 1.65 mm), mean depth 0.77 mm (range 0.35 to 1.61 mm). Paired genital openings carried on prominent swelling located close together ( Fig. 15A ) on posterior margin of ectosoma. No anal opening present. Paired cement glands conspicuous, located in posterior part of ectosoma and extending anteriorly up to 40% of ectosoma length ( Fig. 15 A–C). Egg sacs multiseriate ( Fig. 15D ); typically curved and from 1.4 to 2.5 times longer than ectosoma; mean length 1.69 mm (range 0.88 to 3.87 mm).

Remarks. The original description of M. steenstrupi included data on the external morphology and internal anatomy of the female, based on serial sections, as well as descriptions of the adult male and a late copepodid stage ( Bresciani & Lützen 1961). Bresciani & Lützen (1961) distinguished M. steenstrupi from its congener M. terebellidis , which occurs on what was regarded as the same host at that time (under the name Terebellides stroemi ) by reference to female body size which was up to 1.8 mm in the former compared with up to 4.0 mm in the latter. Based in part on observations made on live material, Bresciani & Lützen (1961) also stated that M. steenstrupi has an ovoid body shape in contrast to the more oblong, conical body of M. terebellidis , and that the paired swellings bearing the female gonopores are larger and positioned closer together in the former than in the latter.

We found that the body shape and form of the genital swellings varies a little according to the state of contraction of the fixed specimens but the basic shape of M. steenstrupi is more globular and can be readily differentiated from the tapering and more flattened M. terebellidis . Our material of M. steenstrupi , with its mean ectosoma length of 1.18 mm for ovigerous females (range 0.57 to 1.94 mm), is smaller than that examined by O’Reilly (2016) who reported a mean length of 1.6 mm (range 1.24 to 1.88 mm). O’Reilly’s material of M. steenstrupi came from the western Scotland, but included some specimens from the southern North Sea, the Celtic Sea and from Kosterfjord ( Sweden).

Previous reports of M. steenstrupi are largely from Terebellides stroemi , however this is now recognised to be a species complex, so the majority of the hosts examined during this study were identified only as T. stroemi - complex. In addition, we report here M. steenstrupi on T. atlantis for the first time.

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.