A novel myxozoan parasite is identified and described from mudskipper, Boleophthalmus dussumieri, collected from a brackishwater ecosystem in Maharashtra, India. Ellipsomyxa boleophthalmi sp. nov. was found in the gallbladder of 58 of 60 fish examined (96.7%). The parasite formed disporous plasmodia that varied in size and shape, and the thin-walled, ellipsoidal and elongated myxospores measured 9.0-10.7 × 6.0-7.8 μm. The two, spherical polar capsules measured 2.7 μm in diameter and enclosed 3-4 coils of polar tubules. Histological observations of infected gallbladder revealed the attachment of disporous plasmodial stages of the parasite to the gallbladder wall with fine pseudopodia. Under the scanning electron microscope (SEM), the myxospores showed a distinct central sutural line and two distinct depressions on the opposite sides at the openings of polar capsules. SEM also revealed the engulfment of microvilli of gallbladder wall by pseudopodia of the plasmodial stages. Analysis of the partial fragment of the SSU rDNA region (1386 bp) showed less than 98% sequence similarity with the other reported Ellipsomyxa spp. In the phylogenetic tree, the present species formed as a distinct subclade within the major clade of Ellipsomyxa spp. The unique morphological and morphometric features of the myxospore, together with the molecular analysis, allowed us to conclude that the present myxozoan is a new species and is named Ellipsomyxa boleophthalmi sp. nov., after the generic name of the host. This is the first report on the occurrence of the genus Ellipsomyxa in B. dussumieri.
Keywords: Boleophthalmus; Ellipsomyxa; Fish parasite; Mudskipper; Myxosporean; Myxozoan.