The marine myxosporean Sigmomyxa sphaerica (Thélohan, 1895) gen. n., comb. n. (syn. Myxidium sphaericum) from garfish (Belone belone (L. )) uses the polychaete Nereis pelagica L. as invertebrate host Author Karlsbakk, Egil Institute of Marine Research, P. O. Box 1870, Nordnes, 5817 Bergen, Norway egil.karlsbakk@imr.no Author Køie, Marianne Marine Biological Laboratory, University of Copenhagen, DK- 3000 Helsingør, Denmark text Parasitology Research 2012 211 2011-06-15 110 1 211 218 http://dx.doi.org/10.1007/s00436-011-2471-8 journal article 298362 10.1007/s00436-011-2471-8 2f5db060-3dd3-4119-a9bc-111af809e567 1432-1955 11376440 Description of actinospores from N. pelagica All actinospores were of the tetractinomyxon type ( Fig. 3 ). They all occurred free in the decaying polychaete body. No pansporocysts were found. The thick-walled actinospores were spherical to slightly ellipsoidal, length 7.0–8.0 (mean 7.6; n =10) and diameter 6.0–7.5 (6.7). The actinospores were composed of eight cells most easily identified by the presence of their nuclei; the three nuclei of the shell valve cells appeared as small thickenings internally on the spore wall, the three nuclei of the polar capsules and the two nuclei of the sporoplasm. The diameter of the three identical spherical polar capsules was 2.0–2.3 (2.1). It was not possible to provoke extrusion of the polar filaments. SSU rDNA sequences Partial SSU rDNA sequences were obtained from M. sphaericum -infected gall bladders of two B. belone from Denmark (sequence isolates SigBel-1 and 2, GenBank accession nos. JN033225, JN033226) and the studied infection from Norway (sequence isolate Msph, JN033227). These were identical (1696 nt compared). Fig. 2 Line drawings of S. sphaerica myxospores from B. belone . a Valvular view and b sutural view. Scale bar 5 μm Table 1 Measurements (in micrometres) of S. sphaerica from B. belone in Denmark and Norway (this study) compared with those published previously from B. belone

Thélohan (1895)	Lubat et al. (1989)	Mladineo et al. (2009)	Present study range (mean±SD; N )
Plasmodia, diameter	20–22	20–22	44 (in image 1A)	21–37
Plasmodia	Disporic	Disporic	Disporic	Disporic a
Spore length	15–20	14–20 (15)	12.95±1.1b	16.7–19.4 (18.0±0.8; 22)
Spore width	7 8c –	7 10 (8)c –	13.16±2.16	10.2–12.8 (11.7±0.8; 19)
Spore thickness	8.17±1.05	7.9–9.1 (8.2±0.6; 4)
PC length	5	5.89±0.98	6.3–9.3 (7.5±0.7; 41)
PC width	3	2.83±0.52	3.5–4.9 (4.0±0.4; 43)
PC coil dia	–	–	2.4–3.5 (2.9±0.3; 27)
PC windings	–	8–9	9–12 (10.3, mode 10; 27)
PC-PC d	–	1.9–4.8 (3.3± 0.9; 21)

a Plasmodia releasing spores seen to contain a second pansporoblast at an early stage in sporogony b Length less than width; likely erroneous c Width and thickness apparently not distinguished d Valvular view Two different parts of a N. pelagica infected with tetractinomyxon actinospores produced two identical partial SSU sequences (sequence isolates Npel 1 and 2, JN033228) (1696 nt compared). These sequences were identical with the M. sphaericum sequences from B. belone , apart for four substitutions (99.8 % identity, 1696 nt compared). On this basis the actinosporean infection in N. pelagica is identified with the myxosporean M. sphaericum infecting B. belone . Blast searches returned Ellipsomyxa spp. as most similar to the partial M. sphaericum SSU rDNA sequences. Phylogenetic analyses on the basis of the SSU rDNA sequences supported a close relationship between genus Ellipsomyxa and M. sphaericum ( Fig. 4 ). Myxidium queenslandicus Gunter and Adlard, 2008 represent a sister group to Ellipsomyxa spp. / M. sphaericum in these analyses ( Fig. 4 ). The congeneric marine clade members M. laticurvum , Myxidium incurvatum Thélohan, 1892 Myxidium gadi Georgévitch, 1916 and M. bergense are not closely related to M. sphaericum ( Fig. 4 ). A schematic illustration of the life cycle of Sigmomyxa sphaerica (syn. M. sphaericum , see below) is shown in Fig. 5 .