Dactylogyrids ( Platyhelminthes : Monogenoidea ) from the gills of Hassar gabiru and Hassar orestis ( Siluriformes : Doradidae ) from the Xingu Basin , Brazil

Four species of Cosmetocleithrum (three new) and one new species of Vancleaveus are described or reported parasitizing the gills of doradid catfishes (Siluriformes) from Xingu River and related tributaries: Cosmetocleithrum phryctophallus sp. nov. and Cosmetocleithrum bifurcum Mendoza-Franco, Mendoza-Palmero & Scholz, 2016 from Hassar orestis; Cosmetocleithrum leandroi sp. nov. from Hassar gabiru; Cosmetocleithrum akuanduba sp. nov. and Vancleaveus klasseni sp. nov. from Hassar orestis and H. gabiru. Cosmetocleithrum phryctophallus sp. nov. differs from its congeners by possessing a male copulatory organ (MCO) with 2 1⁄2 counterclockwise rings, and an accessory piece with an elongate torch-shaped blade. Cosmetocleithrum leandroi sp. nov. has a MCO comprising a coil of about 3 1⁄2 rings, a sigmoid accessory piece with a cup-shaped distal portion, a single type of hooks, and anchors with poorly differentiated roots. Cosmetocleithrum akuanduba sp. nov. is characterized mainly by having a J-shaped MCO, an elongate accessory piece with sharp distal region, distal portion with a small gutter, and a heavily sclerotized vagina with short “S”-shaped vaginal canal. Vancleaveus klasseni sp. nov. differs from the other species of the genus occurring in doradids by possessing anchors with triangular to subtriangular superficial root, developed deep root, and a coiled MCO with 2 1⁄2 counterclockwise rings. Cosmetocleithrum bifurcum was reported for the first time parasitizing doradids from Brazilian Amazon.

During a study of monogenoids infecting doradid fish from the Xingu River and related tributaries, three new species of Cosmetocleithrum and a new species of Vancleaveus (Dactylogyridae) were found parasitizing the gills of Hassar orestis and H. gabiru Birindelli, Fayal & Wosiacki,2011
Gill arches were removed and placed in vials containing heated water (~65 °C).Each vial was vigorously shaken and formalin was added to obtain a 5% solution.In the laboratory, the contents of each vial were examined under a Leica S6D dissecting microscope and helminths were removed from the gills or sediment using small probes.Some specimens were stained with Gomori's trichrome (Humason 1979, Boeger andVianna 2006) and mounted in Damar Gum or Canada balsam to determine internal soft structures and others were mounted in Hoyer's medium or Gray & Wess medium (Humason 1979, Boeger andVianna 2006) for study of sclerotized structures.The measurements, all in micrometers, were obtained according to the procedures of Mizelle and Klucka (1953).Dimensions of organs and other structures represent the greatest measurement in dorso-ventral view; lengths of bent structures (i.e., bars and accessory piece) represent the straight line distances between extreme ends; lengths of anchors follow those presented in Fig. 6; total lengths of the MCO were carried out using IMAGEJ (Rasband 1997(Rasband -2016) ) on drawing tube images.The average measurement is followed by the ranges and the number (n) of specimens measured in parentheses.Illustrations were prepared with the aid of a drawing tube on a Leica DM 2500 microscope with differential interference contrast and phase contrast optics.Definitions of prevalence, mean intensity and mean abundance follow Bush et al. (1997) Description (based on 10 type specimens, 5 mounted in Hoyer, 5 stained with Gomori's trichrome): Body fusiform, total length including haptor 356 (250-462; n = 10) long, 77 (62-95; n = 10) wide at level of germarium.Tegument smooth.(Fig. 1).Cephalic margin rounded, cephalic lobes inconspicuous; 3 or 4 bilateral pairs of head organs with rod-shaped secretion; cephalic glands unicellular, posterolateral to pharynx.Eyes, pigment  Comparative measurements.Table 3.
Etymology.The specific name (a noun) is from Greek (phryctos = burning torch + phallos = penis) and refers to the unique shape of the accessory piece.
Etymology.The specific name is in honor of Dr Leandro Melo de Sousa, Universidade Federal do Pará, Brazil, in recog-nition of his valuable work on the fish diversity of Xingu River, and also because the specific name of the host species, "gabiru", is the nickname of Dr de Souza (Birindelli et al. 2011).Now, Dr de Sousa has the host and parasite named after him.
Etymology.The name akuanduba refers to a divinity called "Akuanduba" of the Arara native people from the Xingu Basin in Pará.According Arara mythic narratives, Akuanduba played his flute to bring order to the world.One day, because of human disobedience, they were thrown into the water.The few survivors had to learn from scratch how to give continuity to life.
Etymology.The species is dedicated to Dr. Gregory J. Klassen in recognition for his work on systematics of monogenoids.
Remarks.Vancleaveus klasseni sp.nov.differs from its congeners by (1) possessing anchors with divergent roots; superficial root triangular to subtriangular, well developed, with conspicuous fold; deep root developed; curved shaft and point; (2) MCO a coiled sclerotized tube with 2 ½ rings, base with sclerotized margin; and (3) accessory piece with small gutter in the distal.

DISCUSSION
There are 14 genera of monogenoidean gill parasites associated with six freshwater siluriform families from Neotropics (Braga et al. 2014, Acosta et al. 2018).From this diversity, 11 species of monogenoids from three genera (i.e., Cosmetocleithrum, Paracosmetocleithrum Acosta, Scholz, Blasco-Costa, Alves & da Silva, 2018 and Vancleaveus) are known parasitizing fishes from the Doradidae (Table 1).The richness of monogenoids parasitizing doradids seems to be variable.The doradid, O. niger is infected with five different species while other species, for example, bear a single or a few species.Considering the recent evaluation of the number of doradid species, approximately 94 species (Birindelli 2014, Sabaj-Pérez andHernández 2017) 1).According to Graça et al. (2013), the occurrence of V. janauacaensis on the erythrinid, Hoplias malabaricus (Bloch, 1794) seems to be accidental since the prevalence and mean intensity were low, 4% of 54 hosts and 1 parasite per infected fish, respectively.
Despite the occurrence of Cosmetocleithrum and Vancleaveus parasitizing the gills of doradids, the most recent cladistic hypothesis for dactylogyrids from catfishes does not support their sister relationship.Mendoza-Palmero et al. (2015) studying partial sequences of the 28S rRNA gene of dactylogyrids, provided a cladistic hypothesis, where monogenoids infecting Neotropical siluriforms are represented by two distinct lineages.In their analysis, species of Vancleaveus appears in a clade with species of Ameloblastella Kritsky, Mendoza-Franco & Scholz, 2000and Unibarra Suriano & Incorvaia, 1995, closely related to other freshwater dactylogyrids (ie., Ancyrocephalus Creplin, 1839, Onchocleidus Mueller, 1936, Ligictaluridus Beverley-Burton, 1984, Actinocleidus Mueller, 1937) parasitizing siluriforms and perciforms with Holartic and Neotropical distributions; while Cosmetocleithrum arises as a sister group of Demidospermus and unidentified dactylogyrids that occur on pimelodid catfishes.Besides these freshwater dactylogyrid taxa from South America, the clade composed by Cosmetocleithrum, Demidospermus and Dactylogyridae spp.also includes marine and freshwater dactylogyrids from Eurasia, Africa and South America, supporting the hypothesis of host switching among species of those genera.Braga et al. (2015) related that the knowledge of phylogenetic relationships of monogenoidean lineages represents the most important information in the task of reconstructing the histories of parasite-host relationships.Understanding patterns in reconstructions of histories in parasite-host systems permits us to manifest possible events of co-speciation, horizontal transference, duplication and extinction.Future studies could elucidate the evolutionary relationships that exist between the lineages on monogenoids and their doradid hosts.The acknowledgement of phylogenetic relationships between the parasite lineages, as well as information about geological events associated with the origin of host-parasite lineages could contribute to a much better comprehension of the evolutionary background involving this host-parasite system.

Table 1 .
List of parasite species of Vancleaveus and Cosmetocleithrum, hosts species, host family, locality and references.AR = Argentina, BR = Brazil, PE = Peru.
. Descriptions of the new species are presented herein.Cosmetocleithrum bifurcum Mendoza-Franco, Mendoza-Palmero & Scholz, 2016 is reported for the first time parasitizing Hassar orestis in Brazilian waters, and the first time parasitizing H. gabiru.

Table 2 .
Host species, number of host specimens collected, localities and respective geographical coordinates.

Table 4 .
Comparative measurements (μm) of specimens of Cosmetocleithrum leandroi sp.nov.from the gills of Hassar gabiru from three locations.
these species differ in the shape of their anchors, i.e., C. longivaginatum has well-defined roots, whereas C. leandroi has poorly differentiated roots.Cosmetocleithrum akuanduba sp.nov.

Table 5 .
Comparative measurements (μm) of specimens of Cosmetocleithrum akuanduba sp.nov.from the gills of Hassar gabiru from three locations.

Table 6 .
Comparative measurements (μm) of specimens of Cosmetocleithrum bifurcum from the gills of Hassar orestis and H. gabiru from Brazil and H. orestis from Peru.BR = Brazil, PE = Peru.

Table 7 .
Comparative measurements (μm) of specimens of Vancleaveus klasseni sp.nov.from the gills of Hassar orestis and H. gabiru from Xingu River Basin.