New data on the acanthocephalan Neoechinorhynchus vill о ldoi Vizcaíno , 1992 ( Neoechinorhynchidae : Acanthocephala ) , based on specimens found in Austrolebias bellottii ( Steindachner , 1881 ) ( Rivulidae : Cyprinodontiformes ) from Punta Indio , Argentina

In a survey of parasites on the killifish, Austrolebias bellottii from Punta Indio and Magdalena, Argentina, the acanthocephalan Neoechinorhynchus villoldoi was found. This parasite had not been recorded since 1992 when it was described for the first time parasitizing Corydoras paleatus (Jenyns, 1842). The type material of N. villoldoi was examined, and with addition of the new specimens, the measurements range was extended. This is the first record of an acanthocephalan in the annual fish, A. bellottii.


Introduction
Data on metazoan parasites of South American annual killifish is scarce.Delgado and Garcia (2015) reported 2 larvae of Contracaecum spp.nematode in Austrolebias spp.from Uruguay, and Luque et al. (2011) mentioned the presence of the nematode Hedruris iheringi Pereira & Vaz, 1933 in Austrolebias bellottii (Steindachner, 1881) from Brazil.Due to a lack of information in Argentina, we began to search for parasites on A. bellottii.
Among genera of the Neotropical fish fauna, the South American killifish genus Austrolebias Costa, 1998 are the most numerous annual fishes distributed in southern Bolivia, southern Brazil, Paraguay, northeastern Argentina and Uruguay with 44 valid species (Costa 2010, Loureiro et al. 2011, Nielsen and Pillet 2015).The genus Austrolebias inhabits temporary wetlands formed during rainy periods and die when the ponds dry out (Costa 2003, Costa 2006).Most species bury their eggs in the substrate, the embryos survive through dry periods in a diapause inside the resistant eggs and hatch at the beginning of the
The fishes grow fast, mostly in the first months of their life, reach the sexual maturity early and begin to spawn (Walford andLiu 1965, Gonzalves et al. 2011).
The short life cycle, the ecological importance, the aquarist interest of this fish, and the scant information on metazoan parasites in killifishes moved us to study the acanthocephalan Neoechinorhynchus villoldoi Vizcaíno, 1992.Based on reexamination of the type material from  Corydoras paleatus (Jenyns, 1842) and the new specimens found parasitizing A. bellottii, we extend the range of measurements of this parasite.This is the first record of N. villoldоi on A. bellottii.

Methods
Fishes (Figs 1,2) were sampled between October and November 2015 from 2 temporary puddles separated from each other by 38 km (Fig. 3).The puddles (Figs 4, 5) were selected randomly and named: site 1 (Punta Indio, 35°18.932ʹS, 057°13.176ʹW) and site 2 (Magdalena, 35° 04.865ʹ S, 057°31.627ʹW).The collections were made with a frame of 1 × 0.50 m and a net-mesh of 0.5 × 0.5 cm.The specimens were transported to the lab in plastic bags with oxygenated water from the collection sites.The fishes were sacrificed by medullar section.The viscera were examined for parasites under a binocular microscope.The acanthocephalans found were cleared as temporary mounts with Lacto-phenol or stained with dehydrated chlorhidric carmin mounted in Canada balsam, and studied under an Olympus Bx51 microscope (Tokyo, Japan).The drawings were made with a drawing tube.The structures were photographed with an AmScope MU 1000 10 MP digital camera (USA) attached to the microscope and measured using ImageJ software (Schneider et al. 2012).The mean followed by minimum and maximum values in parenthesis are given in micrometers (µm), unless stated otherwise.Figures 1  and 2 were photographed with a Canon 7D camera with a Canon 100 mm 2.8 macro lens and Figures 4 and 5 with a Canon 50 mm 1.8 Macro lens.The vouchers were deposited in the Helminthological Collection of the Museo de La Plata, Argentina, under the number MLP-He 7150.
Examined material included all the type series of Neoechinorhynchus villoldoi, 1537 C, 1539 C, 1541-44 C and 1547-50 C, in the Helminthological Collection of Museo de la Plata.

Results
The prevalence, median intensity and abundance of N. villoldoi from A. bellottii are provided in Table 1.
Description of N. villoldoi found in A. bellottii.Small, cylindrical, with gigantic hypodermic nuclei 1 or 2 dorsal and 1-3 ventral (not drawn), posterior end rounded.Genital pore subterminal in both sexes.Small proboscis, cylindrical, 18 hooks in 3 circles of 6 hooks each.Site 1 at Punta Indio is 7 km away from Villoldo stream (the type locality of N. villoldоi) but 35 km from site 2. The distance between sites could be one of the reasons for the absence of this parasite in fishes from Magdalena (site 1).
Corydoras paleatus (the type host) and A. bellottii are fishes with different habitat but perhaps they prey over the same food item.The diets of both species are represented mainly by microcrustaceans (Cladocera, Copepoda, and Ostracoda), and immature aquatic insects (Chironomidae) (Escalante 1983, Grosman 2002, Laufer 2009, Keppeler 2014).Better knowledge of the life cycle of N. villoldоi could clarify if this parasite uses 1, 2 or more intermediate hosts, and if both fishes prey over the same or different intermediate host?" Knowledge of the parasite fauna of A. bellottii is important because this fish forms a link between micro-and macroecosystems.Killifishes mainly feed on microcrustaceans and immature aquatic insects, and killifishes serve as food for aquatic birds (Keppeler et al. 2016).They are also important fishes for aquarists due to the high number of species, bright colors, size and the relatively easy breeding in captivity.
There are many species of Austrolebias, and the genus has a wide distribution, and therefore we suspect that our record N. villoldоi in A. bellottii is only the first of a several new records (or new species) of adult metazoan parasites and larval stages waiting for to be discovered in these "killis".Female (Figs 14-17) 3-4 × larger than the males, reproductive system includes uterine bell, selector of eggs, utero and vagina.Eggs elongated (Fig. 18).Measurements of male and female structures provided in Table 2.

Discussion
Neoechinorhynchus villoldoi is the first acanthocephalan found in a killifish of the genus Austrolebias.This is the second record for this acanthocephalan since the discovery of N. villoldoi by Vizcaíno (1992).
Our examination of the type series material deposited by Vizcaíno (1992) of N. villoldоi have similar measurements with the acanthocephalans found now in A. bellottii, but some minor differences can be distinguished.The type material included mostly juvenile females (only one mature with eggs) and males in poor conservation stage, and this could account for why some of the original measurements have a wide range.
The presence of N. villoldоi in this newly recorded host, A. bellottii, could be attributed to: (a) the proximity to the

Table 1 .
Number of specimens of Austrolebias bellottii examined (N).Prevalence of infection, mean intensity and mean abundance of Neoechinorhynchus villoldоi in sample sites.