Abstract
The present paper describes a novel species of Myxobolus parasitizing the gill filaments of the largescale mullet, Planiliza macrolepis from Cochin backwaters, Kerala, India. The parasite develops in the gill filaments; plasmodia elongated, milky white, measured 1.37-2.18 (1.78 ± 0.35) mm × 0.07-0.12 (0.10 ± 0.02) mm in size. Mature myxospores ovoid in valvular view, biconvex in sutural view with smooth shell valves and measured 6.24-7.02 (6.63 ± 0.23) × 5.01-6.18 (5.68 ± 0.25) μm in size. Polar capsules equal, oval with pointed anterior ends, 3.07-3.58 (3.33 ± 0.12) × 1.68-2.42 (2.09 ± 0.18) μm in size. Polar filamentswith 4 coils, measured 29.61 ± 4.75μm in length when extruded. Sporoplasm binucleate with a rudimentary nucleus and a vacuole. A comparison with related Myxobolus species revealed significant morphological and morphometric differences. In BLASTN and genetic distance analysis, the present parasite showed high divergence with other myxosporean sequences, indicating its molecular uniqueness. In Maximum Likelihood and Bayesian Inference analysis, the present species stands out with M. ramadus as sister branch within the Myxobolus clade. In infected gill filaments, the plasmodia caused swelling/deformation, compression of lamellae and reduction in respiratory surface area. Three of 222 P. macrolepis screened were infected, indicating a prevalence of 1.3%. Considering the morphological, morphometric, molecular and phylogenetic differences with the previously described species of myxosporeans, along with the dissimilarities in host and geographical locations, the present parasite is treated as a new species and the name Myxobolus cochinensis n. sp. is proposed.
Highlights
Myxosporeans are a diverse, exclusively microscopic, group of metazoan parasites belonging to the phylum Cnidaria
The present study describes a new species of myxosporean, M. cochinensis n. sp. infecting the largescale mullet, P. macrolepis from Cochin backwaters
Myxospore morphology and morphometry constitute the foundation for myxosporean systematics, recent advances in molecular systematics using 18S SSU rDNA based phylogenetic inferences have greatly improved the perception of myxosporeans (Ye et al 2014)
Summary
Myxosporeans are a diverse, exclusively microscopic, group of metazoan parasites belonging to the phylum Cnidaria. The genus Myxobolus is characterized by bivalvular myxospores which are ellipsoidal to ovoid or rounded in valvular view and biconvex in sutural view; with smooth shell valves and two pyriform, sometimes unequal polar capsules and binucleate sporoplasm, often with an iodinophilous vacuole. They are histozoic in nature, infecting various tissues as intercellular or sometimes intracellular cysts (Lom & Dykova 2006)
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