Pareiorhina hyptiorhachis, a new catfish species from Rio Paraíba do Sul basin, southeastern Brazil (Siluriformes, Loricariidae)

Abstract Pareiorhina hyptiorhachis is described from Ribeirão Fernandes and Rio Pomba, Rio Paraíba do Sul basin, Brazil. The new species is distinguished from its congeners (Pareiorhina brachyrhyncha, Pareiorhina carrancas, Pareiorhina cepta, and Pareiorhina rudolphi) by the presence of a conspicuous ridge on the trunk posterior to the dorsal fin (postdorsal ridge), simple teeth, a completely naked abdomen, a round dorsal profile of the head, greater suborbital depth and greater head width. We discuss the distributional pattern of the new species and its congeners and hypothesize that headwater capture is responsible for the distribution of Pareiorhina species across different watersheds in southeastern of Brazil.


Palavras chaves
Cascudinhos, Taxonomia, Água Doce, Neoplecostominae, Região Neotropical introduction The genus Pareiorhina was proposed by Gosline (1947) to include Rhinelepis rudolphi Miranda- Ribeiro, 1911 and is currently included in the subfamily Neoplecostominae (sensu Chiachio et al. 2008;Roxo et al. 2012aRoxo et al. , 2012b. Recently, three new species have been described: P. carrancas by Bockmann and Ribeiro (2003); P. brachyrhyncha by Chamon et al. (2005); and P. cepta by Roxo et al. (2012c). In their description of P. carrancas, Bockmann and Ribeiro (2003) proposed a combination of characters to separate Pareiorhina from other genera of Loricariidae: the lateral borders of the head lacking hypertrophied odontodes; unicuspid teeth; a naked abdomen; dorsal plates meeting along the mid-dorsal line between the dorsal and caudal fins; adipose fin absent; ventral plates covering the mid-ventral line behind the anal-fin base; and the dorsal portion of the body behind the dorsal fin flattened. However, no exclusive synapomorphies were presented to diagnose the genus. Recently, the molecular studies of Cramer et al. (2011) and Roxo et al. (2012aRoxo et al. ( , 2012b have found that Pareiorhina may not be monophyletic. An examination of the fish collections at the Laboratório de Biologia e Genética de Peixes de Botucatu (LBP) and Museu de Ciências e Tecnologia, Pontifícia Universidade Católica do Rio Grande do Sul (MCP) revealed the existence of an undescribed Pareiorhina species from the Rio Paraíba do Sul basin, Brazil. This new species is formally described herein.

Material and methods
All measurements were taken from point to point to the nearest 0.1 mm using digital calipers (except the postdorsal ridge depth, which was measured using a stereomicroscope and analyzed using the software Axio Vision Release 4.8.2). Counts were taken from the left side when possible. In the description, counts are followed by their frequencies in parentheses. The measurements followed Bockman and Ribeiro (2003), except for the folded dorsal-fin length and the snout-opercle length that were not included in that publication. We added the following measurements from Carvalho and Reis (2009): mandibular ramus, suborbital depth and unbranched anal-fin ray length. We also added the measurement of postdorsal ridge depth (from the base of the postdorsal ridge to its upper portion). Osteology was performed on specimens cleared and double-stained (c&s) according to the procedures of Taylor and Van Dyke (1985). The osteological and the body-plate nomenclature followed Schaefer (1997). Vertebral counts were obtained from clearedand-stained specimens and included the first five vertebrae modified into the Weberian apparatus. The compound caudal centrum (PU1 + U1; Lundberg and Baskin 1969) was counted as one vertebra. The pores nomenclature followed Arratia and Huaquin (1995). Asterisks in the text refer to the holotype. After collection the animals were anesthetized using 1% benzocaine in water and fixed in 10% formalin for at least two days, then transferred to 70% ethanol for permanent storage for morphological studies.
All examined material was housed at the following
Description. Morphometric and meristic data are given in Table 1. In lateral view, dorsal profile of body strongly convex from snout tip to distal margin of supraoccipital; straight from supraoccipital to dorsal-fin origin; slightly decreasing to end of caudal peduncle. Ventral surface of body, slightly concave at head portion, straight to convex from posterior end of head to pelvic-fin insertion, and straight but angled to posterior end of caudal peduncle. Snout tip rounded in dorsal view. Nostril small. Trunk and caudal peduncle rectangular in cross-section.
Greatest body depth at dorsal-fin origin. Body progressively narrowing posteriorly from cleithrum. Head flat to slightly convex between orbits; superior margin of orbits elevated. Eye small, orbital diameter 11.1-15.5% of HL, situated dorsolaterally just posterior of midpoint of head. Rostral margin of snout with minute, posteriorlydirected odontodes; numerous small odontodes on dorsal portion of head. Opening of swimbladder capsule small. Perforations of compound pterotic distributed on whole bone, greater and more concentrated on its ventral margin; its openings nearly rounded in median region, and irregular along inferior and posterior margins of bone. Lips large; oral disk rounded, papillose; premaxillary teeth 22 (1), 29 (1) Dorsal-fin rays ii,7; dorsal-fin originating at vertical through posterior end of pelvicfin base; distal margin slightly convex. Pectoral-fin rays i,6; distal margin slightly convex; unbranched pectoral-fin ray reaching middle of unbranched pelvic-fin ray; unbranched pectoral-fin ray covered with large and pointed odontodes. Pelvic-fin rays i,5; distal margin of fin slightly convex; tip of adpressed pelvic fin almost reaching anal-fin origin; unbranched pelvic-fin ray covered with conspicuously pointed and well-developed, and uniformly distributed odontodes which are larger at ventral portion. Anal-fin rays i,5; distal margin slightly convex. Caudal fin rays i,7-7,i. Adipose fin absent. Caudal fin truncated with ventral unbranched principal ray longer than dorsal ray. Body entirely covered by bony plates, except for ventral surface of head, abdomen and region overlaying swimbladder capsule. Dorsal series of plates 24-26, mid-dorsal 17-21, median perforated plates 24-26, mid-ventral 17-22, and ventral 19-22. Trunk with conspicuous, elongated, postdorsal ridge formed by 13-15 raised, unpaired, median plates; ridge continuous posteriorly with procurrent caudal-fin rays. Head lacking crest. Head and body plates covered with minute, uniformly sized and distributed odontodes. Seven pairs of ribs associated with vertebrae 8-14. Ribs slender and poorly ossified. Total vertebrae 29.
Supraorbital sensory canal with four pores; pore s1 located on prenasal plate below nasal plate; pore s3 located on posterior portion of nasal; pore s6+s6 located between frontal plates, on horizontal line through anterior limits of eye; pore s8 located on division between frontals, sphenotic and supraoccipital plates, just above eye. Infraorbital sensory canals with six pores; pore io1 located on anterior portion of first infraorbital; pore io2 located in medial region between first and second infraorbitals; pore io3 located in medial region between second and third infraorbitals; pore io4 located in medial region between third and fourth infraorbitals; pore io5 located in medial region between fourth and fifth infraorbitals and pore io6 located between sixth infraorbital and sphe-notic. Preopercular canal with three pores; pore pm2 located on ventral portion of cheek plate, pore pm3 located between cheek plate and preopercle; pore pm4 located between preopercle and compound pterotic. Two postotic pores; pore po2 located just above of branchial slit; pore po3 located in region of overlying opening of swim-bladder capsule.
Color in alcohol. Two body-coloration patterns observed. First pattern (Fig. 1): Ground color of dorsal surface of head and body yellowish brown. Ventral surface of body and head lighter than dorsal with dark spots of melanophores widely separated. Three dark saddles on dorsal surface of trunk (in some specimens not present), most anterior one inconspicuous. Lateral portion of body with inconspicuous dark stripe from head to caudal fin. Pectoral, pelvic and dorsal fins with three irregular, poorly defined bands. Caudal fin with variegated blotches. Second pattern (Fig. 4): Ground color of body uniformly dark except, ventral portion of body mostly clear; Fins with inconspicuous, irregularly defined bands: one in anal fin, two in pectoral and pelvic fins. Dorsal and caudal fins entirely dark.
Sexual dimorphism. Males with a papilla at urogenital opening and fewer teeth in premaxillary 22-39 (vs. 32-44 females) and 17-32 dentary (vs. 30-45 females).  Etymology. The specific name, hyptiorhachis is a combination of Greek, hyptios = supine, lying on the back, and rhachis = ridge, midrib, and is in reference to the conspicuous postdorsal ridge found in this species.
Distribution and habitat. Pareiorhina hyptiorhachis is known from Rio Pomba and one of its tributaries, the Ribeirão Fernandes, in the municipality of Santa Barbara do Tugúrio, Minas Gerais State, Brazil (Fig. 5). This species inhabits moderate to fast-flowing streams, with a substrate of rocks and sand and margins covered by aquatic vegetation. Specimens were collected in association with loose stones, on the streambed. The new species is syntopic throughout its distribution with Astyanax sp., Characidium sp., Geophagus brasiliensis, Harttia cf. carvalhoi, Imparfinis sp., Neoplecostomus microps, Trichomycterus cf. alternatus, and Trichomycterus sp. Bockmann and Ribeiro (2003) proposed seven characters to diagnose Pareiorhina. The new species described herein, P. hyptiorhachis, possesses all of these characters. On the other hand, Pareiorhina did not form a monophyletic group in the molecular analysis of Roxo et al. (2012aRoxo et al. ( , 2012b; in that analysis, P. hyptiorhachis, cited as Pareiorhina sp. 1, appeared as the sister group of P. carrancas, and these two species formed the sister group of Neoplecostomus. Furthermore, P. rudolphi, the type species of Pareiorhina was the sister group of Pseudotocinclus. Considering that P. hyptiorhachis exhibits all of the characters listed by Bockmann and Ribeiro (2003) for Pareiorhina, the molecular data conflict with the available morphological data for Neoplecostominae, and new morphological studies in Neoplecostominae are in progress (Edson Henrique Lopes Pereira, pers. comm.), we prefer to include P. hyptiorhachis in Pareiorhina rather than in another Neoplecostominae genus or in a new genus.

Discussion
Pareiorhina hyptiorhachis is similar to P. carrancas from the upper Rio Paraná basin. The two species share unicuspid teeth and the presence of a postdorsal ridge of unpaired plates, although the postdorsal ridge is better developed in P. hyptiorhachis (all female and male samples) (Fig. 2). Moreover, the new species has more raised median unpaired plates in the postdorsal ridge (13-15 vs. 10-13 in P. carrancas). The close relationship between P. hyptiorhachis and P. carrancas suggested by the molecular data of Roxo et al. (2012b) is thus at least superficially supported by morphology.
Pareiorhina is distributed across three hydrographic basins, with P. rudolphi, P. brachyrhyncha and P. hyptiorhachis from the Rio Paraíba do Sul basin; P. carrancas from the upper Rio Paraná basin; and P. cepta from the Rio São Francisco basin. Ribeiro et al. (2006) suggested that the activation of old faults in southeastern Brazil during the Miocene and Pliocene resulted in several headwater captures between adjacent drainages of the São Francisco, upper Paraná and Coastal rivers. Roxo et al. (2012a) suggested that the lineage that gave rise to P. carrancas and P. hyptiorhachis was from the upper Rio Paraná basin and that P. hyptiorhachis reached the Rio Paraíba do Sul basin about 6.2 (2.3-11.2) million years ago, probably through headwater captures between the upper Paraná and several coastal drainages (Rio Paraíba do Sul and Ribeira do Iguape basin) during the late Miocene. Chamon et al. (2005) suggested that the evolutionary history of P. rudolphi and P. brachyrhyncha was linked to Pleistocene and pre-Pleistocene climatic fluctuations that may have temporarily isolated hillside streams at or near the headwaters of the Ribeirão Grande, producing the events that subsequently led to the sympatry of P. brachyrhyncha and P. rudolphi. However, as suggested by Crammer et al. (2008, 2011), Chiachio et al. (2008 and by Roxo et al. (2012aRoxo et al. ( , 2012b, P. brachyrhyncha and P. rudolphi do not share an exclusive most recent common ancestor, which negates the hypothesis of Chamon et al. (2005). Additionally, Roxo et al. (2012a) suggested that the origin of the lineages that gave rise to the species of Pareiorhina were much older, originating in the ) million years ago for Pareiorhina rudolphi and 6.27 (2.33-11.21) million years ago for Pareiorhina carrancas plus P. hyptiorhachis (Pareiorhina sp. 1 in Roxo et al. 2012a)].