A new species of Jainus ( Monogenea ) , gill parasite of Schizodon borellii ( Characiformes , Anostomidae ) from the upper Paraná river floodplain , Brazil

Jainus piava n. sp. is described from the gills of Schizodon borellii (Boulenger, 1900) (Characiform), commonly named as piava from the upper Paraná River floodplain, Brazil. The new species differs from the other members of Jainus in the following features: ventral bar thin broadly V-shaped and male copulatory organ (MCO) a coil of about 1.5 rings. Jainus piava n. sp. is similar to species of Jainus by having a ventral anchor base with flattened superficial root and elongate rodlike deep root.


Introduction
According to Pavanelli et al. (2004), in Brazil there have been few studies about the ecology of freshwater fish parasites.This occurs due to a scarcity of systematic works on fish parasites.The upper Paraná River floodplain has 153 fish species; of these, around 12 species belong to the family Anostomidae (AGOSTINHO et al., 2004).
During a helminthological study on the freshwater fish Schizodon borellii (Boulenger, 1900) in Brazil, locally known as piava (GRAÇA; PAVANELLI, 2007), a new species of Jainus was found and described from the gills.

Material and methods
Eleven specimens of S. borellii were collected from September 2006 to September 2007 with nets in the upper Paraná river floodplain (22º50' -22º70'S and 53º15' -53º40'W), southern Brazil.Monogeneans were removed from the gills under stereo-microscope, killed in a 1:4000 formalin solution and preserved in 5% formalin.Some Acta Scientiarum.Biological Sciences Maringá, v. 33, n. 2, p. 227-231, 2011 specimens were mounted unstained in Hoyer's medium to study sclerotized structures.Other specimens, stained with Gomori's trichrome, were used to visualize internal organs (EIRAS et al., 2006).Measurements are in micrometers, with means followed by the range and number of specimens or structures measured in parentheses.
Illustrations were prepared with the aid of a drawing tube and a Nikon YS 2 microscope.Ecological terminology is based on Bush et al. (1997).
Numbering (distribution) of haptoral hook pairs follows Mizelle (1936), and the description of coiled tube of the male copulatory organ followed the suggestions of Kritsky et al. (1985).Type specimens were deposited in the Instituto Oswaldo Cruz Collection (CHIOC), Rio de Janeiro State, Brazil.Tegument thin and smooth.Cephalic lobes poorly developed or absent: head organs and cephalic glands inconspicuous or absent, accessory granules sparse in cephalic area.Eyespots four or six, provided by aggregations of dark-brown granules.Pharynx muscular; esophagus bifurcated in two intestinal crura usually posteriorly confluented.One testis, one ovary tandem or overlapping.Seminal vesicle a dilated portion of the vas deferens; prostates reservoir one or two.Genital pore ventral between pharynx and copulatory complex.Male copulatory organ and accessory piece articulated or nonarticulated proximally.Base of male copulatory organ adorned or not.Male copulatory organ with coils or not.Vagina sinistral (KRITSKY et al., 1987).Haptor with one pair of ventral anchors.Dorsal anchor base bifurcate with well-developed superficial and deep roots.Ventral anchor base with flattened superficial root end elongate rodlike deep root.Ventral anchor shaft reduced or absent, apparently incorporated into point and/or base.Anchor filaments frequently absent.Two transverse nonarticulated bars, each connecting bases of an anchor pair.Ventral bar with or without median anterior and often presence of a delicate posterior projection.Hooks 14, similar in shape; distributed as described by Mizelle (1936) except the pair one which may lies posterior to ventral bar.Vitellaria distributed randomly in trunk or as two bilateral bands confluent near pharynx and in posterior trunk.Parasites of Neotropical Characiformes.

Dactylogyridae
Remarks: The description of the genus was based in two other species: Jainus jainus Mizelle, Kritsky & Crane, 1967  Etymology: the specific name refers to the popular host's name.

Discussion
Jainus was proposed by Mizelle et al. (1968) for monogeneans of Neotropical Characiformes.Before this work, the genus of this parasite comprised four species distributed in Southeast Amazon river basin and Costa Rica.Three species of Jainus were described from Characiformes of Southern America as follows: J. jainus from Chalceus macrolepidotus Cuvier, 1818; J. robustus from Creatochanes affinis (Güinther, 1864); J. amazonensis from Brycon melanopterus (Cope, 1872); and one from Costa Rica, J. hexops from Astyanax fasciatus (Cuvier, 1819).
The genus Jainus resembles Urocleidoides Mizelle & Price, (1964), by the presences of a male copulatory organ and nonarticulated proximally accessory pieces (MIZELLE et al., 1968).Jainus differs in the morphology of the copulatory complex and especially the ventral anchors.The dorsal anchors in Jainus possess a base with conventional superficial and deep roots and can be considered the normal anchor type for most Ancyrocephalinae.However, the ventral anchor base is characterized by a rodlike deep root.Considering Jainus piava n. sp., four species of Jainus have previously been described from South America.The new species closely resembles the other members of Jainus by presenting a ventral anchor base with flattened superficial root and elongate rodlike deep root.Jainus piava n. sp.can be distinguished from J. robustus, J. amazonensis, J. jainus and J. hexops by the ventral bar without median anterior and delicate posterior projection and the morphology of the copulatory complex.
Jainus jainus and J. robustus have an accessory piece nonarticulated to the base of male copulatory organ, dorsal bar arched posteriorly (MIZELLE et al., 1968).Jainus piava n. sp.differs from these species by having accessory piece articulated and is similar to the others species by dorsal bar arched.This last character can be observed also in J. amazonensis (KRITSKY et al., 1980).Jainus amazonensis is also similar to J. piava sp.nov.by the prostatic pyriform reservoir, lying ventral to seminal vesicle, male copulatory organ with counterclockwise ring coiled, ventral bar broadly V-shaped.Kritsky et al. (1987) resurrected Characidotrema Paperna & Thurston, 1968, so far considered as synonymy of Jainus Mizelle, Kritsky & Crane, 1968by Paperna (1973).Both genera possess several similar and somewhat unique characteristics such as robust bodies with poorly developed peduncles and haptors; modified ventral anchor-bar complexes; overlapping gonads; strongly developed vitellaria; and both taxa are restricted as parasites of characoid fishes.Species of Characidotrema has a relatively uniform morphology of the haptoral sclerites and dextral vagina, wich is fundamentally different from the Neotropical species of Jainus (KRITSKY et al., 1980).This is the first dactylogyrid monogenean described from Schizodon borellii.

Conclusion
Jainus piava n. sp. is similar to species of Jainus by having a ventral anchor base with flattened superficial root and elongate rodlike deep root but differs from the other members of Jainus in the following features: ventral bar thin broadly Vshaped and male copulatory organ (MCO) a coil of about 1.5 rings.
and J. robustusMizelle,  Kritsky & Crane, 1967, subsequently otKayton, 1980ies were described J. hexopsKritsky & Leiby,  1972 and J. amazonensis Kritsky, Thatcher andKayton, 1980both with absent some characteristics in the description of the genus, such as variation in the number of eyes and articulation of the base accessory piece of the MCO.