A new species of Tereancistrum ( Monogenea , Dactylogyridae ) from the gills of three Leporinus species ( Characiformes , Anostomidae ) and a revised description of Tereancistrum parvus

The present study describes Tereancistrum flabellum n. sp. (Dactylogyridae, Ancyrocephalinae) from the gills of the anostomid fishes Leporinus friderici, Leporinus amblyrhynchus and Leporinus elongatus from two freshwater ecosystems in the south east of Brazil. This new species is mainly characterized by the morphology of the copulatory complex (such as the MCO base formed by two fan-shaped structures, and accessory piece flattened, curved, rigid and channeled), a dorsal anchor with a well-developed superficial and inconspicuous deep root, and the shape of the accessory anchor sclerite with small spathulate termination. Tereancistrum flabellum n. sp. is the first record of a dactylogyrid from L. amblyrhynchus. The description of Tereancistrum parvus is also emended to correct and complement previous descriptions and the species is reported for the first time in Schizodon nasutus.


INTRODUCTION
The Anostomidae Günther, 1864 family includes fish species that are widely distributed from southern Central America to tropical and subtemperate regions of South America (Nelson 2006).Many anostomid species are recognized by their habit of feeding in an inclined position, and constitute a significant part of the fish biomass in different aquatic habitats (Garavello and Britski 2003).
Leporinus Agassiz, 1829 is the most diverse genus among anostomids, with 87 species, while the Schizodon Agassiz, 1829 genus is represented by 14 species (Nelson 2006).Some larger members of Leporinus and Schizodon are known for their spawn migrations in the Paraná-Paraguay river system and in the Amazon and Orinoco basins.
Because of their annual migrations, these species are subjected to significant exploitation by commercial and subsistence fisheries as an important food source for the people of South America (Garavello and Britski 2003).
Although monogeneans are common fish parasites, despite the efforts of taxonomists their diversity in the Neotropics remains largely unknown (Cohen et al. 2013).Dactylogyridae Bychowsky, 1933 is the most abundant taxon in South America, and included in this family is Tereancistrum Kritsky, Thatcher and Kayton, 1980, which accommodates parasites of characiform fishes in the Neotropical region (Thatcher 2006).
During an investigation of helminth fauna of fish from the Sapucaí-Mirim River and Jurumirim Reservoir in the south east of Brazil, specimens of an undescribed species of Tereancistrum were recovered from the gills of Leporinus friderici (Bloch, 1974), Leporinus amblyrhynchus Garavello andBritski, 1987 andLeporinus elongatus Valenciennes, 1850.The present study describes this new species and compares it with closely related species of the genus.We also present new data on the morphology of T. parvus and report its occurrence in S. nasutus for the first time.
The ZooBank Life Science Identifier (LSID) of this publication is: urn:lsid:zoobank.o r g : p u b : 0 5 5 5 7 6 6 5 -9 F C 4 -4 2 3 7 -8 C 8 B -982278EF1948.The fishes were collected using a nylon monofilament gillnet between 5:00 PM and 7:00 AM, totaling 14 hours of exposure.The capture of fish specimens from the Sapucaí-Mirim River was authorized under a Permanent License for the Collection of Zoological Material (SISBio 13794-1), while collection from the Jurimirim Reservoir was authorized by the Department of the Development of Fishery and Inspection/DEFOP (License #SP/538/88).All animal procedures were performed in full compliance with the Ethics Committee for Animal Experimentation (protocol #120) of the Universidade Estadual Paulista (São Paulo State University -UNESP).The fish specimens collected were individually stored in plastic bags and placed in a Styrofoam box with ice for immediate transportation to the laboratory.

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The gills were removed and placed in vials containing hot water with a temperature of around 60°C.After that, they were shaken, and absolute ethanol was added (Thatcher 2006).The monogeneans were collected and stored in 70% ethanol solution.Samples of these parasites were stained with Gömöri's trichrome and mounted in Canada balsam for analysis of internal organs.Some specimens were mounted in Hoyer's and Gray and Wess medium for the study of sclerotized structures (Kritsky et al. 1986).
Morphological and morphometric analysis of parasites was carried out using a computerized system for image analysis with differential interference contrast (DIC) -LAS V3 (Leica Application Suite V3; Leica Microsystems, Wetzlar, Germany).The illustrations of the sclerotized structures were performed with the aid of a camera lucida mounted on a Leica DMLS microscope with phase contrast optics.All measurements were presented in micrometers (μm) and expressed as means, followed by the range and number of specimens measured (n) in parentheses.The prevalence and mean intensity of infestation was calculated in accordance with Bush et al. (1997).
Voucher host fish specimens were deposited in the fish collection of the Laboratório de Biologia e Genética de Peixes (Fish Biology and Genetics Laboratory) (LBP)
Etymology: The specific name is derived from the Latin (flabellum = fan), and refers to the shape of the cirrus base.

REMARKS
Based on the presence of ventral anchors with accessory anchor sclerite articulated to the tip of the superficial root, one pair of eyespots, overlapping gonads, and due to having a typically ancyrocephaline hook distribution (Mizelle 1936), the new species proposed in this study is considered to be a member of the Tereancistrum genus (Kritsky et al. 1980).The new species can be distinguished from most of its congeners by the morphology of its copulatory organ (MCO and accessory piece), which mainly has a fan-shaped cirrus base.The new species resembles T. paranaensis in the shape of its ventral and dorsal anchors, but can be differentiated by the number and direction of its MCO rings (3.5 clockwise rings in T. flabellum n. sp.; 1.5 to 2.5 counterclockwise rings in T. paranaensis), the shape of its accessory piece, and the dorsal (with antero-median indentation and slightly expanded ends in T. flabellum n. sp. and rectangular in T. paranaensis) and ventral bars (evenly curved with slightly expanded ends in T. flabellum n. sp. and rectangular in T. paranaensis).
Tereancistrum ornatus and T. curimba are morphologically closed to T. flabellum n. sp. in relation to the accessory anchor sclerite, but differs in the dorsal bar (evenly curved with slightly expanded ends in T. flabellum n. sp.; and Y-shaped in T. ornatus and T. curimba), the number and direction of its MCO rings (3.5 clockwise rings in T. flabellum n. sp.; 1 ¼ counterclockwise rings in T. ornatus and T. curimba), the shape of accessory piece, and the dorsal anchor (with well-developed superficial, inconspicuous deep root, evenly curved shaft, point in T. flabellum n. sp.; and widely divergent roots of anchor base, short shaft and straight point in T. ornatus and T. curimba).
Tereancistrum parvus differs from the new species in relation to the direction of its MCO rings (clockwise in T. flabellum n. sp.; counterclockwise in T. parvus), dorsal bar (evenly curved with slightly expanded ends in T. flabellum n. sp.; and V-shaped in T. parvus), and dorsal anchor (welldeveloped superficial, inconspicuous deep root, evenly curved shaft, point in T. flabellum n. sp.; and slightly curved shaft, short point in T. parvus).

REMARKS
Tereancistrum parvus was originally described parasitizing specimens of L. fasciatus from the Steinhart Aquarium, San Francisco, USA, by Kritsky et al. (1980).This description was based on a single specimen and presents sclerotized structures of the haptor and MCO only.Two redescriptions of T. parvus were recently proposed and added new data on the morphology of internal organs such as the position of the vagina, testis, ovary, seminal vesicle and the egg morphology (Karling et al. 2014, Wendt et al. 2015).However, some morphological differences were observed in relation to these previous descriptions and they are presented herein to correct and complement the diagnosis of T. parvus.Firstly, the morphology of the MCO is different mainly in terms of the shape of the accessory piece, which consists of a rigid piece, slightly wider at the posterior region and narrower in the anterior region, where it ends in a small projection (Figure 10, present study).The plates of the accessory piece is not clear in the description by Karling et al. (2014) [see Figure 4g in Karling et al. (2014)], and it was represented by Wendt et al. (2015) as a tube with an opening along its lateral extent [see Figure 2b in Wendt et al. (2015)].Furthermore, while Wendt et al. (2015) stated that the terminal projection of the accessory piece described in the original description by Kritsky et al. (1980) was absent, this characteristic was observed in the present study.In addition, the morphology of the vaginal aperture in the present study is different to that described by Wendt et al. (2015) [see Figure 2d in Wendt et al. (2015)], and is more closely related to that represented by Karling et al. 2014[see Figure 3 in Karling et al. (2014)].Wendt et al. (2015) stated that the ventral bar is V-shaped, but in fact it is the dorsal bar that has this shape, as described by Kritsky et al. (1980) and confirmed by Karling et al. (2014).In summary, some morphological differences observed in T. parvus may also be linked to intraspecific variation according to the fish host species.
Tereancistrum spp.have variable MCO shapes, with the most common being a coiled tube (with clockwise or counterclockwise rings), which is present in seven species.However, two species exhibit a different MCO pattern, either a simple tapered tube (T.kerri) or a strongly arched tube (T.arcuatus).The majority of species of Tereancistrum have counterclockwise rings (four species), while two species (T.flabellum n. sp. and T. ornatus) present clockwise rings.The vagina can be dextral or sinistral in Tereancistrum spp., while only two species (T.kerri and T. flabellum n. sp.) have a dextral vagina.Tereancistrum paranaensis needs more attention and should be revised, as in the original description the position of the vagina is dextral while the MCO presents clockwise rings (Karling et al. 2014).Two new revisions of this species were later performed, both of which confirmed that the vagina is sinistral, although one states that the rings of the MCO are counterclockwise (Wendt et al. 2015), while the other reports the opposite (Abdallah et al. 2016).
The prevalence of T. flabellum n. sp. in the Sapucaí-Mirim River was higher in L. friderici (55%) than in L. elongatus (31.8%) and L. amblyrhynchus (25%).However, L. friderici exhibited a lower prevalence (15.5%) in the Jurumirim Reservoir, which may be related to the number of fish specimens analyzed in each environment, which was higher in the Jurumirim Reservoir, or due to the inherent environmental characteristics of each sample site.
Tereancistrum parvus was most prevalent (62.5%) in S. nasutus, among the fish species analyzed in this study.The prevalences of this monogenean in L. friderici (12.5%) and L. elongatus (10%) were similar to those reported by Guidelli et al. (2011) in the floodplain of the Upper Paraná River, Brazil (3.8% and 17.9%,respectively).
The present study represents the first record of dactylogyrids -T.flabellum n. sp. and T. parvus for L. amblyrhynchus and S. nasutus, respectively.Leporinus elongatus and L. friderici were also parasitized by T. flabellum n. sp. and T. parvus in the Sapucaí-Mirim River, and L. friderici was parasitized by T. flabellum n. sp. in the Jurumirim Reservoir, in the south east of Brazil.These findings extend our knowledge of the host-parasite relationship and geographical distribution of this monogenean genus in the Neotropical region.
ALINE C. ZAGO et al. flabellum n. sp.; 1 ¼ counterclockwise rings in T. toksonum), the shape of accessory anchor sclerite, ventral (with antero-median indentation, slightly expanded ends in T. flabellum n. sp.; and formed by thin sclerotized membrane with thick posterior margin in T. toksonum) and dorsal bar (evenly curved with slightly expanded ends in T. flabellum n. sp.; and Y-shaped in T. toksonum), and dorsal

TABLE I Measurements of Tereancistrum flabellum n. sp. in other hosts (Leporinus amblyrhynchus and Leporinus elongatus) from the Sapucaí-Mirim River, south east of Brazil.
(well-developed superficial, inconspicuous deep root, evenly curved shaft, point in T. flabellum n. sp.; and with long divergent roots, short shaft and straight point in T. toksonum).Tereancistrum arcuatus differs from the new species by the MCO (a coiled tube of 3.5 clockwise rings in T. flabellum n. sp.; and a strongly arcuate sclerotized tube in T. arcuatus), the shape of accessory anchor sclerite (with small spathulate termination in T. flabellum n. sp.; and with longitudinal groove in T. arcuatus), and dorsal anchor (well-developed superficial, inconspicuous deep root, evenly curved shaft, point in T. flabellum n. sp.; and with robust base, poorly differentiated roots and long straight shaft in T. arcuatus).Tereancistrum pirassununguensis can be differentiated from the new species in relation to the numbers and direction of its MCO rings (3.5 clockwise rings in T. flabellum n. sp.; and 2 counterclockwise rings in T. pirassununguensis), the shape of accessory anchor sclerite (with small spathulate termination in T. flabellum n. sp.; and with a little groove at the end in T. pirassununguensis), * Measurements are in micrometer (µm), and the mean is followed by the range.anchorREDESCRIPTIONTereancistrum

parvus Kritsky, Thatcher and Kayton, 1980
uterus, and eggs not observed.Vitelline follicles coextensive with intestinal cecum and absent near reproductive organs.