Description of Myxidium pseudocuneiforme n. sp. (Myxosporea: Myxidiidae) from Cyprinus carpio in China, with the resolution on a taxonomic dilemma of Myxidium cuneiforme.

Investigations on myxozoan parasites of fish from Chongqing in China, revealed two Myxidium cuneiforme-like myxosporeans infecting the gallbladder of Cyprinus carpio carpio and Carassius auratus. We researched their myxospore morphology, and analyzed their genetic similarity and phylogenic relationships to other myxozoans based on small subunit ribosomal DNA (18S rDNA) sequences. Although both parasites recovered were morphologically similar, the myxosporean isolated from C. auratus was consistent in morphology to Myxidium cuneiforme, which was described from this host species. The parasite isolated from C. c. carpio had overlapping myxospore dimensions to M. cuneiforme, but on average, the polar capsules were not as long. More importantly, this parasite was genetically distinct from M. cuneiforme with 96.3% and 96.5% similarity in two sequences of 18S rDNA, and we propose the name Myxidium pseudocuneiforme n. sp. for this myxozoan from common carp. Its mature myxospores are ellipsoidal and asymmetric with pointed ends in valvular view, arc-shaped or fusiform in sutural view. The pyriform polar capsules are equal in size, and polar filament with 5-6 coils. This study highlights that molecular characteristics and host specificity are indispensable for myxozoan species identification when presented with the taxonomic dilemma of whether we are observing one species that exhibits slight morphological differences or multiple, but similar, species in different hosts.

Morphological and molecular identification of Myxobolus parakoi sp. nov (Myxozoa: Myxobolidae), from Cyprinus carpio in Chongqing China.

During an ongoing investigation into the myxosporean diversity of common carp in Chongqing, China, Myxobolus parakoi sp. nov. was found to infect the gill lamellae of Cyprinus carpio (Linnaeus, 1758). Both morphological and SSU rDNA data revealed that M. parakoi sp. nov. was distinct from other myxosporeans. Mature myxospores of M. parakoi sp. nov. were pyriform in the frontal view. The spores were 15.98 ± 0.78 (14.59-17.72) µm in length and 7.84 ± 0.78 (6.66-9.75) µm in width. The two polar capsules were pyriform and equal in size, exhibiting 8.72 ± 0.50 (7.76-9.92) µm in length and 3.03 ± 0.23 (2.63-3.56) µm in width. Polar filaments within the polar capsules were coiled with 11 or 12 turns. Phylogenetic analysis revealed that M. parakoi sp. nov. and Myxobolus koi (FJ710800) were clustered together, forming a sister subclade with Myxobolus tanakai. This study also implied that the morphology of the myxospores was generally correlated with their phylogenetic relationship, while such correlation was not strong or consistent.

Morphological and Molecular Identification of a Novel Species, Ceratomyxa siganicola n. sp. (Myxozoa: Ceratomyxidae) from Siganus fuscescens, in East China Sea.

INTRODUCTION: Ceratomyxa Thélohan, 1892 is one of the largest genera under Myxosporea Butschli, 1881, and has a worldwide distribution, but little attention has been paid to myxosporean parasites from the Chinese seawaters, East China Sea. METHODS: Morphology and molecular biology methods were combined for species identification and phylogenetic analysis. RESULTS: A new coelozoic myxosporean species, Ceratomyxa siganicola n. sp., was found to infect the gallbladder of Siganus fuscescens (Houttuyn, 1782) (Perciformes, Siganidae) from coastal waters of Xiamen, East China Sea, China. Mature myxospores of the novel species exhibited the morphologically typical features of the genus Ceratomyxa. They were slightly crescent shaped with rounded ends, measuring 5.6 ± 0.5 (4.8-6.5) µm in length and 19.1 ± 1.8 (16.0-22.1) µm in thickness. The posterior angle was slightly convex to straight and measured 177.1 ± 0.5 (175.2-178.4)°. Spore valves were slightly unequal and smoothly ovoid in the lateral view. Two polar capsules were spherical, equal in size and measured 2.7 ± 0.2 (2.1-3.0) µm in diameter. The 18S rDNA sequence of C. siganicola n. sp. was unique among all myxozoans, and the highest similarity was 97.4% with Ceratomyxa barnesi. Phylogenetic analysis showed that C. siganicola n. sp. was clustered within the clade of siganid ceratomyxids. The present results also indicated that the species radiation of Ceratomyxa occurred not only within host affinity but also within locality.