Description of Myxobolus balatonicus n. sp. (Myxozoa: Myxobolidae) from the common carp Cyprinus carpio L. in Lake Balaton

Synopsis of the species of Myxobolus (Cnidaria, Myxozoa, Myxosporea) described between 2014 and 2020

A synopsis of the species of Myxobolus Bütschli, 1882 (Cnidaria, Myxosporea, Myxobolidae) described from 2014 up till now is presented. It includes 122 nominal species described all over the world. For each of the species, the most relevant morphological and morphometric data, as well as data are provided related to the location in the host, type host and type locality. The GenBank accession numbers are provided whenever possible, and the spores were redrawn based on the original descriptions. The bibliography includes all the papers containing the species descriptions.

Morphological, histopathological and molecular characterization of Thelohanellus theinensis n. sp. (Cnidaria: Myxosporea) infecting an Indian major carp, Labeo bata in a cold water wetland in Punjab (India)

A myxozoan parasite belonging to the genus Thelohanellus Kudo, 1933 (Myxosporea, Bivalvulida) was isolated from the gill lamellae of Labeo bata (Hamilton, 1822) inhabiting Ranjit Sagar Wetland in Northern parts of Punjab, India. Histopathology of the infected gills indicated lamellar distortion due to the presence of plasmodia. The intensity of infection was recorded to be moderate as indicated by gill plasmodial index (GPI = 2). The plasmodia were microscopic, ovoid, creamish white, 2.0-4.0 mm in diameter containing 300-400 number of myxospores. The myxospores were broadly pyriform in shape, measuring 8.27 × 4.41 µm, having a prominent pore at the anterior end. The polar capsule was pyriform in shape, measuring 4.15 × 4.10 µm, containing a polar filament coiled perpendicular to the longitudinal axis of myxospore body making 6-7 turns. At molecular level, the analysis of 18S rDNA sequence of T. theinensis n. sp. demonstrated maximum homogeneity of 99 % with T. filli (KR340464) as only 2 gaps were found due to the difference of the last 20 base pairs at the 3' end of T. theinensis n. sp. The current study emphasizes the need for caution when dealing with members of species complex.

A novel myxosporean parasite Myxobolus klamathellus n. sp. (Cnidaria: Myxosporea) from native blue chub (Gila coerulea) in Klamath Lake, Oregon

Blue chub, Gila coerulea Girard, 1856 is a freshwater cyprinid fish native to inland drainages of western North America. It has not previously been recorded as a host of any myxosporean parasite (Cnidaria: Myxosporea), despite myxosporeans being cosmopolitan in freshwater and marine fishes worldwide and sympatric with this host. Herein, we describe a novel myxosporean from subcutaneous cysts in native blue chub from Klamath Lake, Oregon. Myxospores were consistent with genus Myxobolus, being obovoid but compressed in thickness, length 14.3 ± 0.4 (13-15) μm, width 9.7 ± 0.4 (9-10) μm, thickness 7.7 ± 0.3 (7-8) μm; two polar capsules ovoid slightly dissimilar in size, length 6.4 ± 0.4 (6-7) μm, width 3.8 ± 0.3 (3-4) μm, with four (3-5) turns of the polar filament (tubule); capsule openings apical, one in each valve cell. The small subunit ribosomal DNA sequence was up to 97 % similar to Myxobolus spp. from other cyprinids from North America and Europe. Given the novel host, unique myxospore morphometrics, and DNA sequence, we describe this as Myxobolus klamathellus n. sp.

Correlation between host specificity and genetic diversity for the muscle-dwelling fish parasite Myxobolus pseudodispar: examples of myxozoan host-shift?

Myxobolus pseudodispar Gorbunova, 1936 (Myxozoa) is capable of infecting and developing mature myxospores in several cyprinid species. However, M. pseudodispar isolates from different fish show up to 5% differences in the SSU rDNA sequences. This is an unusually large intraspecific difference for myxozoans and only some of the muscle-dwelling myxozoan species possess such a high genetic variability. We intended to study the correlation between the host specificity and the phylogenetic relationship of the parasite isolates, and to find experimental proof for the putatively wide host range of M. pseudodispar with cross-infection experiments and phylogenetic analyses based on SSU rDNA. The experimental findings distinguished 'primary' and less-susceptible 'secondary' hosts. With some exceptions, M. pseudodispar isolates showed a tendency to cluster according to the fish host on the phylogenetic tree. Experimental and phylogenetic findings suggest the cryptic nature of the species. It is likely that host-shift occurred for M. pseudodispar and the parasite speciation in progress might explain the high genetic diversity among isolates which are morphologically indistinguishable.

Testicular myxosporidiasis and ultrastructural characteristics of Myxobolus bufonis (Myxobolidae) infecting the Egyptian toad Bufo regularis (Bufonidae). A light and electron microscopic study

The phylum Myxozoa comprises more than 2180 species, almost all of which are considered to be obligate parasites of aquatic fishes and amphibians. They are dangerous pathogens responsible for severe economic losses. From March to September 2014, 40 adult male Bufo regularis (Bufonidae) captured from different areas at Giza province, Egypt, were surveyed for myxosporean parasitic infection. Of these, 22 (55%) were infected by histozoic plasmodia, which produced spores after rupture belonging to Myxosporidia. The present investigation introduced a new data for the recorded parasite observed by light and transmission electron microscopy. The infection was diagnosed as large clusters of macroscopic plasmodia embedded in the testicular tissue causing distortion at the site of infection. The host reaction was manifested by the encapsulation of the plasmodia with a thick layer of connective tissue. Plasmodia were whitish in color, elliptical to ovoid in shape measuring 0.54 ± 0.2 (0.34-0.63) mm in diameter. The spores were subspherical, reaching 7.1 ± 0.2 (6.2-8.4) μm in length and 6.3 ± 0.2 (5.8-7.0) μm in width with two equal-sized polar capsules regularly arranged at the anterior pole of each spore. They were 3.4 ± 0.2 (3.0-4.2) μm in length and 1.9 ± 0.2 (1.6-2.4) in width with 6-8 turns of polar filaments. Ultrastructural analysis showed that the plasmodia were surrounded by a plasma membrane with numerous projections and pinocytotic channels extended toward the host cell. The generative cells and the different developmental stages were arranged at the periphery of the plasmodia while immature and mature spores were centrally arranged. Sporogenesis, capsulogenesis, valvogenesis, and spore maturation of the present parasite were also described.