Synopsis of the species of Ortholinea Shulman, 1962 (Cnidaria: Myxosporea: Ortholineidae)

Syst Parasitol (2024) 101:37 https://doi.org/10.1007/s11230-024-10155-2 Synopsis of the species of Ortholinea Shulman, 1962 (Cnidaria: Myxosporea: Ortholineidae) Luis F. Rangel · Sónia Rocha Maria J. Santos · Received: 10 January 2024 / Accepted: 20 February 2024 / Published online: 3 May 2024 © The Author(s) 2024 Abstract A synopsis of Ortholinea Shulman, 1962 (Cnidaria: Myxosporea: Ortholineidae) is presented and identifies 26 nominal species presently allocated within this genus. Species morphological and morphometric features, tissue tropism, type-host, and type-locality are provided from original descriptions. Data from subsequent redescriptions and reports is also given. Accession numbers to sequences deposited in GenBank are indicated when available, and the myxospores were redrawn based on original descriptions. The information gathered shows that Ortholinea infect a wide taxonomic variety of freshwater and marine fish. Nonetheless, the broad host specificity reported for several species is not fully L. F. Rangel (*) · M. J. Santos Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), Laboratory of Animal Parasitology and Pathology, University of Porto, Matosinhos, Portugal e-mail: L. F. Rangel · M. J. Santos Laboratory of Animal Parasitology and Pathology, Biology Department, Faculty of Sciences (FCUP), University of Porto, Porto, Portugal S. Rocha Instituto de Investigação e Inovação em Saúde (i3S), University of Porto, Porto, Portugal S. Rocha Institute of Biomedical Sciences Abel Salazar (ICBAS), University of Porto, Porto, Portugal supported by morphological descriptions and requires molecular corroboration. The members of this genus are coelozoic and mainly parasitize the urinary system, with few species occurring in the gallbladder. Ortholinea visakhapatnamensis is the only exception, being histozoic in the visceral peritoneum. Molecular data of the small subunit ribosomal RNA gene (SSU rDNA) is available for about one third of Ortholinea species, with genetic interspecific variation ranging between 1.65% and 29.1%. Phylogenetic analyses reveal Ortholinea to be polyphyletic, with available SSU rDNA sequences clustering within the subclades of the highly heterogenous freshwater urinary clade of the oligochaete-infecting lineage. The life cycles of two Ortholinea species have been clarified based on molecular inferences and identify triactinomyxon actinospores as counterparts, and marine oligochaetes of the family Naididae as permissive hosts to this genus. Introduction The class Myxozoa Grassé, 1970 comprises microscopic obligate cnidarian parasites. There are more than 2,200 known myxozoan species, presently distributed among 66 genera and 20 families (Fiala et al., 2015; Freeman & Kristmundsson, 2015; Freeman et al., 2020). The subclass Myxosporea Bütschli, 1881 is the most diversified, encompassing species characterized by a complex life cycle that require Vol.: (0123456789) 13 37 Page 2 of 16 annelids (oligochaetes, polychaetes, and sipunculids) as definitive hosts, and vertebrates (usually fish, but also birds, reptiles, and mammals) as intermediate hosts (Lom & Dyková, 2006). The family Ortholineidae Lom & Noble, 1984 is particularly heterogenous, comprising three coelozoic genera that parasitize marine fish - Ortholinea Shulman, 1962, Neomyxobolus Chen & Hsieh, 1960 and Kentmoseria Lom & Dyková, 1995 - but also, two histozoic genera parasitizing freshwater fish - Cardimyxobolus Ma, Dong & Wang, 1982, and Triangula Chen & Hsieh, 1984. The oldest species presently included in the genus Ortholinea were originally described as belonging to the genus Sphaerospora Thélohan, 1892, family Myxidiidae Thélohan, 1892 (Thélohan, 1892). Davis (1917) considered the latter to be extremely heterogenous and, therefore, instituted the family Sphaerosporidae to include the genera Sphaerospora and Myxoproteus Doflein, 1898. This author also created the genus Sinuolinea to better encompass Sinuolinea dimorpha (Davis, 1916), originally described as belonging to the genus Sphaerospora. Later, Shulman (1959) instituted the family Sinuolineidae to include the genus Sinuolinea, comprising species with myxospores having a sinuous suture line, and the genus Davisia Laird, 1953, comprising species with myxospores having lateral processes. Shulman (1962) expanded the family Sinuolineidae with the creation of the genus Ortholinea for encompassing species with myxospores having a straight suture line, i.e., O. divergens Thélohan, 1895, O. orientalis Shulman & Shulman-Albova, 1953 and O. polymorpha Davis, 1917 (originally included in the genus Sphaerospora). Ortholinea divergens was established as type species. Lom and Noble (1984) created the family Ortholineidae within the also newly established suborder Variisporina, which united the members of the former suborders Bipolarina Tripathi, 1948 emend. Shulman, 1959 and Eurysporea Kudo, 1919 emend. Shulman, 1962. The family Ortholineidae was created to accommodate the genera Ortholinea and Neomyxobolus, which are coelozoic and develop myxospores with polar capsules that are in the same plane as the suture line, unlike the remaining genera of the family Sinuolineidae, in which the polar capsules are located perpendicular to the suture line (Lom & Noble, 1984). The genera Cardimyxobolus, Triangula and Kentmoseria were later added to the family Ortholineidae, despite the first two differing from all other Vol:. (1234567890) 13 Syst Parasitol (2024) 101:37 genera included in this family based on their histozoic development (Lom & Dyková, 2006). Currently, the taxonomic classification of the genus Ortholinea is: Phylum Cnidaria Hatschek, 1888 Class Myxozoa Grassé, 1970 Subclass Myxosporea Bütschli, 1881 Order Bivalvulida Shulman, 1959 Suborder Variisporina Lom & Noble, 1984 Family Ortholineidae Lom & Noble, 1984 Genus Ortholinea Shulman, 1962 Type species Ortholinea divergens (Thélohan, 1895) Shulman, 1962 Following the creation of the family Ortholineidae, other Sphaerospora species were ultimately transferred to the genus Ortholinea, namely Sphaerospora undulans Meglitsch, 1970 and Sphaerospora sphaerocapsularae Wierzbicka 1986 (Arthur & Lom, 1985; Sitjà-Bobadilla & Álvarez-Pellitero, 1994). In turn, three species have been transferred from Ortholinea to other genera. Parvicapsula irregularis (Kabata, 1962) was originally described as Sphaerospora irregularis, and later redescribed by Gaevskaya and Kovaleva (1984) as Myxoproteus irregularis. Unknowing of this taxonomic alteration, Arthur and Lom (1985) transferred S. irregularis to the genus Ortholinea. The validity of this species, however, was questioned by Køie et al. (2007), who suggested it to be more related with Parvicapsula Shulman, 1953; an assumption that was ultimately confirmed by Kodádková et al. (2014) through molecular analyses. The species Triangula perccotti (Dogiel & Akhmerov, 1960 in Akhmerov, 1960) was also originally described (...truncated)