Myxidium sphaericum, Thelohan, 1895, Thelohan, 1895

Karlsbakk, Egil & Køie, Marianne, 2012, 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, Parasitology Research (211) 110 (1), pp. 211-218 : 212-213

Description of M. sphaericum from B. belone

Plasmodia were spherical to irregular ( Fig. 1a, b ), attached to gall bladder epithelium or free, often with brushy region representing the zone of epitheliar adhesion. Parts of plasmodia with distinct ectoplasm when unsporulated ( Fig. 1a ), while ectoplasm often not apparent in fully sporulated ones ( Fig. 1a, b ). Plasmodia contained refractive granules, scattered or in aggregations, increasing in number during sporogony. Mature plasmodia were usually markedly vacuolate ( Fig. 1b ). Plasmodia were generally disporic, rarely tetrasporic. Sporogony was disporic. Occasionally, plasmodia releasing spores were seen to contain a second sporoblast at an early stage in sporogony. Plasmodia without spores measured up to 36 μm in average diameter (N = 16), plasmodia with immature spores 20–30 μm (N =4), and plasmodia with two mature spores 23–37 μm (mean 28 μm, N =11).

Spore main outline was ellipsoid ( Fig. 1c ), but valvular protrusions were associated with the tip of the polar capsules (PC), giving a sigmoid appearance in sutural view and spindle shape in valvular view ( Fig. 2 ). Immature spores were occasionally crescent shaped. Valves were smooth, thicker along the ellipsoid outline of the main spore body and thin surrounding the protruding part of the PCs ( Fig. 1c, d ). Suture was weakly sigmoid, faint and symmetrical ( Fig. 2 ). PCs were terminal, equal, elongate pyriform, PC axis in medial plane in valvular view, but with an angle reaching c. 47° to spore axis in sutural view. Polar filament coils are perpendicular to PC axis, with filament coil diameter averaging 70% of PC diameter. Coils are not present in the protruding part of the PCs ( Fig. 1c–e ). Polar capsule length to spore length was 1:2.1–2.8 (mean 2.3± 0.2; N =21). Fully extruded polar filaments reach 134– 153 μm in length. Sporoplasm was binucleate, filling the barrel-shaped spore cavity between the PC cells. Spore measurements are given in Table 1 .

Figures

Fig. 1 Plasmodia and myxospores of S. sphaerica from the gallbladder of B. belone. a Plasmodium (flattened) without visible indication of sporogony, showing distinction between ecto- and endoplasm. b Sporulated plasmodium (flattened) showing spores in valvular view, vacuolate appearance and refractive granules. Note that any polar capsule lengths taken in valvular view may be erroneously short due to their oblique orientation in the spores. c Spore in sutural view. d, e Spores as seen in the focal plane of one polar capsule, showing polar filament coils and the valvular extensions associated with the protruding part of the capsules. Scale bars a, b 10 μm, c, d 5 μm

Fig. 2 Line drawings of S. sphaerica myxospores from B. belone. a Valvular view and b sutural view. Scale bar 5 μm