Myxobolus turpisrotundus (Myxosporea: Bivalvulida) spores with caudal appendages: investigating the validity of the genus Henneguya with morphological and molecular evidence

Abstract

Spores of the myxozoan parasite Myxobolus turpisrotundus Zhang 2009 were observed for the first time bearing caudal appendages. Most spores had the typical Myxobolus spp. morphology, but approximately 10% of spores possessed a spore body that was slightly elongated with a short tail projecting from the spore valve. In other spores, the tail was much more clearly visible and elongate. The spore body of these unusual spores is consistent in morphology and dimension to the normal spores of M. turpisrotundus. Both spore types were found within individual cysts, and the small subunit ribosomal RNA (ssrRNA) gene sequence from parasite cysts of this type was nearly identical to the previously published sequence of M. turpisrotundus from allogynogenetic gibel carp Carassius auratus gibelio (Bloch). The phenomenon of Myxobolus spores with caudal appendages provides additional evidence that the use of this character to separate Myxobolus and Henneguya into distinct genera is not reflective of an evolutionarily accurate classification scheme. Phylogenetic analysis of ssrDNA sequence from Myxobolus and Henneguya species showed clustering of species in some locations of the tree, but ultimately these genera are intermixed. The use of a single character to delineate species in the two most species-rich myxozoan genera has been consistently challenged where DNA analyses are used. The present finding of a single species bearing both Myxobolus-type and Henneguya-type spores emphasizes the inadequacy of this classification scheme, and highlights the need for careful consideration of these variable characteristics when describing myxozoan species.

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

“…was not a valid feature for characterisation of the genus. Recently, some Myxobolus species have been reported with appendages similar to those of Henneguya species (ElMansy 2005, Bahri 2008, Liu et al 2010b, 2013a, which supports the opinion of Kent et al (2001). In the present study, we also observed 11% of the spores with caudal appendage.…”

“…However, phylogenetic studies based on the ribosomal DNA sequence data do not support a separation of these two genera (Kent et al 2001, Fiala 2006, Fiala and Bartošová 2010, Liu et al 2010b, Carriero et al 2013. Kent et al (2001) speculated that the caudal appendage of Henneguya spp.…”

Supplemental description and molecular characterization of Myxobolus miyarii Kudo, 1919 (Myxosporea: Myxobolidae) infecting intestine of Amur catfish (Silurus asotus)

“…The reported species in the present work were highlighted in bold and species with spores of blunted anterior end underlined challenges the traditional taxonomy (Bahri 2008;Liu et al 2010Liu et al , 2014Zhang et al 2014) and suppression of Henneguya was also suggested (Kent et al 2001). In the present study, caudal appendages were firstly reported for some of spores of M.miyairii which is the ninth reported Myxobolus species with tailed spores after M. bizerti, M. mulleri, M. heterosporus, M. turpisrotundus, M. musseliusae, M. tsangwuensis, M. oralis, and M. khaliji (Bahri 2008;Liu et al 2010Liu et al , 2013Liu et al , 2014Zhang et al 2014). Interesting, two types of tailed spores (single tail or bifurcated tail) were firstly observed from most of plasmodia of M. miyairii which make it distinguished from the definition of Henneguya.…”

Myxobolus pseudowulii sp. n. (Myxozoa: Myxosporea), a new skin parasite of yellow catfish Tachysurus fulvidraco (Richardson) and redescription of Myxobolus voremkhai (Akhmerov, 1960)

“…Owing to their negative impact on fish, myxosporeans have attracted much attention (Lom and Dyková 2006, Liu et al 2010a, Fiala et al 2015, Velasco et al 2016. To date, approximately 2,300 myxosporean species have been described based on spore morphology (Fiala et al 2015).…”