Histopathological and ultrastructural studies of Myxobolus turpisrotundus from allogynogenetic gibel carp Carassius auratus gibelio in China.

During an ongoing systematic survey on species diversity of myxozoans parasitising allogynogenetic gibel carp Carassius auratus gibelio (Bloch) in China, plasmodia were detected in the fins, lip, jaw, gill chamber, gill arches, operculum and oral cavity of infected fish. Combining the morphological and molecular data, the present species was identified as Myxobolus turpisrotundus Zhang, Wang, Li et Gong, 2010. Histopathological examination revealed that despite infecting different organs, M. turpisrotundus always occurred in dermis, demonstrating its affinity to this tissue. Histopathological effect of M. turpisrotundus on the host is relatively mild except parasites in the gill arches producing compression of the adipose tissue and heavy adductor muscles deformation with lymphohistiocytic infiltrates. In addition, the plasmodia in different sites were with the same complex structure arrangement: cup-like cells with unknown derivation, a thin collagenous fibril layer, areolar connective tissue, basement membrane and host epithelial cell. Ultrastructural analysis showed that the parasite has monosporic pansporoblast and sporogenesis followed the usual pattern of most of the myxosporeans.

Myxobolus oralis sp. n. (Myxosporea: Bivalvulida) infecting the palate in the mouth of gibel carp Carassius auratus gibelio (Cypriniformes: Cyprinidae).

During a survey on the myxosporean fauna of gibel carp Carassius auratus gibelio (Bloch) in China, a species of Myxobolus Bütschli, 1882 that did not conform to any known species was found. The species is characterised by the presence of round to ellipsoidal plasmodia of 2.6-4.0 mm in diameter in the palate of host. Mature spores are obovate in frontal view and lemon-shaped in lateral view, with the following range, mean and standard deviation of dimensions: 10.8-12.8 µm (11.7 ± 0.4 µm) long, 8.2-9.9 µm (8.9 ± 0.4 µm) wide and 6.0-7.5 µm (6.8 ± 0.3 µm) thick. Two polar capsules are pyriform, 4.0-5.5 µm (4.8 ± 0.3 µm) long by 2.9-3.6 µm (3.0 ± 0.2 µm) wide. Polar filaments are coiled, with 5 to 6 turns. A small proportion of spores possesses a short caudal process. Scanning electron microscopy revealed discoid spores with a low sutural ridge and middle bulge. The small subunit ribosomal DNA sequence of this species did not match any available sequences in GenBank. Phylogenetically, this species is sister to M. nielii (Nie et Li, 1973) and M. hearti Chen, 1998 in a Henneguya-Myxobolus clade with robust support. Given the morphological and molecular differences between this species and other Myxobolus species, we propose the name Myxobolus oralis sp. n. for this parasite from gibel carp.

Ultrastructure, surface topography, morphology and histological observations of a new parasitic cnidarian of the marbled swamp eel from the world's largest tropical wetland area, Pantanal, Brazil.

Myxosporeans are a diverse group of microscopic cnidarians of wide distribution that evolved into a parasitic lifestyle. A new myxosporean species, Myxobolus sp., is herein described infecting the mandible of wild specimens of Synbranchus marmoratus, caught in the world's largest tropical wetland area, Pantanal, Brazil. Light, scanning, transmission electron microscopy and histological observations unveiled detailed taxonomic information of the new myxosporean cnidarian. Ultrastructural analysis revealed a detailed description of plasmodia structures which can be used for comparison with plasmodia from other species of myxobolids. Both histological and ultrastructural observations evidenced a connective tissue capsule surrounding the plasmodia of Myxobolus sp. as a histopathological host reaction to the infection of this parasitic cnidarian. Histology showed that tissue tropism of the new myxosporean occurs in a well-defined part of the mandible, with development of plasmodia occurring in the epidermis layer. Mature myxospores from the valvular view featured an ovoid shape and had a short prolongation of the spore valves in the posterior end. Myxospores measured 22.7 ± 1.2 µm (21.5-23.9 µm) in length, 12.5 ± 0.4 µm (12.1-12.9 µm) in width and 11.3 ± 0.5 (10.8-11.8 µm) in thickness. Polar capsules were pyriform equally-sized and measuring 4.6 ± 0.3 µm (3.9-4.3 µm) in length and 2.9 ± 0.1 µm in width (2.8-3.0 µm). Finally, this study substantiates the still hidden myxosporean diversity from South America.