First report of Pterinotrematoides mexicanum Caballero & Bravo-Hollis , 1955 ( Monogenea , Macrovalvitrematidae ) in Micropogonias furnieri ( Desmarest , 1823 ) ( Perciformes , Sciaenidae ) from the coastal zone of the state of Rio Grande do Sul , Brazil

In South America, Pterinotrematoides mexicanum Caballero & Bravo-Hollis, 1955 has been reported in the state of Rio de Janeiro, Brazil, and in Argentina parasitizing Micropogonias furnieri (Des marest, 1823). In this paper, the first record of P. mexicanum in the same host from the coastal zone of the state of Rio Grande do Sul, Brazil is presented, filling a gap of occurrence of P. mexicanum. The morphology of P. mexicanum is re described and compared with that of Neopterinotrematoides avaginata Suriano, 1975.

Until now, the only monogenean species reported in M. furnieri from the state of Rio Grande do Sul were Neomacrovalvitrema argentinensis Suriano, 1975, and Neopterinotrematoides avaginata Suriano, 1975(Velloso and Pereira Jr. 2010).This is the first report of P. mexicanum parasitizing the Whitemouth croaker, M. furnieri, from the coastal zone of the state of Rio Grande do Sul, Brazil.
Specimens of M. furnieri (n = 3) were obtained from professional fisherman in July and August 2014 in the municipality of Rio Grande (32°11′06″ S, 052°06′32″ W), and from public market in Porto Alegre, in the State of Rio Grande do Sul, Brazil.Gills were placed in a 1:4000 formalin solution and shaken at least 50 times (Amato 1994).The monogeneans found in the samples were fixed in 5% formalin, stained with Semichon's carmine and mounted in Faure's medium or stained and mounted according to the procedures described by Gallas et al. (2014).
All measurements are given in micrometers (μm), unless otherwise indicated, and represent the range followed by the mean ± standard deviation, and sample size (in parenthesis).Ecological terminology follows Bush et al. (1997).The genus and species determinations of the monogeneans were based on Yamaguti (1963) and Caballero and Bravo-Hollis (1955), respectively.The line drawings were prepared using a drawtube and the photomicrographs were taken with a camera Sony DSC-W55 attached to the microscope.Representative specimens of the helminth were deposited in the  Caballero & Bravo-Hollis, 1955 Figures 1-9.
The measurements of the specimens are similar to those found in literature, although some variation in body length was observed.Specimens collected parasitizing Micropogon sp. and A. rhomboidalis in the Pacific Ocean (Tantaleán et al. 1985;Fuentes-Zambrano et al. 2009), tend to be larger than those found in M. furnieri in the Atlantic Ocean (Caballero and Bravo-Hollis 1955;Suriano 1966;Kohn et al. 1989;present study).
Difference were also found in the number and morphometry of the hooks of the larval haptor, with two pairs of hooks being found in the present study-as in Tantaleán et al. (1985) and Fuentes-Zambrano et al. ( 2009)-in contrast with three pairs in the studies of Caballero and Bravo-Hollis (1955) and Kohn et al. (1989).The specimens examined by Caballero and Bravo-Hollis (1955) were smaller in size than those examined by Tantaleán et al. (1985) and in the present study.The differences found in the oncotaxy of the larval haptor may be related to one of two distinct processes.One would be the loss of one of the pairs of hooks (Tantaleán et al. 1985;Fuentes-Zambrano et al. 2009), while the other possibility would be the difficulty of visualizing one of the lateral pairs, which may have been mistaken for the lateral border of the haptor (Caballero and Bravo-Hollis 1955;Kohn et al. 1989).The difference in the length of the hooks may be related to a scaling error, given that the hook is considerably longer than the scale used (Caballero and Bravo-Hollis 1955).
Neopterinotrematoides avaginata appears to differ from P. mexicanum only by the absence of a vagina (Kohn et al. 1989), which may not be sufficient to consider this form to be a valid species, but Kohn et al. (1989) did not evaluate other structures, such as the shape of ovary or the ventral valve of the ventral clamp and the posterolateral sclerites of the dorsal clamp.Comparing the description of N. avaginata by Suriano (1975) with the specimens of P. mexicanum examined in the present study, other traits were identified which help differentiate the two species.In P. mexicanum, for example, the ovary is shaped like an inverted U, and restricted to the anterior third of the body, whereas in N. avaginata the ovary is shaped like an inverted J and reaches as far as the middle region of the body.In P. mexicanum, in addition, the ventral valve of the ventral clamp is longer than wider, whereas in N. avaginata it is wider than longer, and in P. mexicanum, the posterolateral sclerites of the dorsal clamps are divided into anterior and posterior portions, while in N. avaginata, the sclerites are laterally contiguous.As mentioned above, a systematic review of these genera is required, and this should be based on a comprehensive examination of holotype and paratype material.
On the Atlantic coast of South America, P. mexicanum has been reported in the state of Rio de Janeiro (Kohn et al. 1989;Alves andLuque, 2000, 2001a, b;Fernandes et al. 2009) and in Argentina (Suriano 1966).This is the first report of P. mexicanum from the coastal zone of the State of Rio Grande do Sul, Brazil, providing important new insights into the geographic distribution of the species.The present study constitutes the first detailed description of the sclerotized structures of the species since its description.