A new species of Otothyropsis ( Siluriformes : Loricariidae ) from the rio Paraguay basin , Paraguay

Otothyropsis piribebuy, new species, is described from the río Piribebuy, a tributary to the río Paraguay basin, Cordillera, Paraguay. The new species is distinguished from O. marapoama mainly by having a continuous mid-dorsal series of 17-18 lateral plates, a robust levator crest in the hyomandibula, naked areas in the abdomen, an unpigmented circular blotch on the median portion of the lower lobe, and by several features related to sexual dimorphism. In addition, Otothyropsis is rediagnosed and its phylogenetic relationships are discussed based on its present diversity.


Introduction
Otothyropsis Ribeiro, Carvalho & Melo, 2005 is a monotypic genus if Hypoptopomatinae, a loricariid subfamily that includes about 126 species (Eschemeyer & Fong, 2011) distributed in 19 genera.The hypoptopomatine cascudinhos are small fishes with a wide distribution along the cis-Andean river drainages from Venezuela to northeastern Argentina (Schaefer, 2003).Otothyropsis and its type species O. marapoama were described by Ribeiro et al. (2005), who also included the species in the phylogenetic scheme of Schaefer (1998).Ribeiro et al. (2005) recovered Otothyropsis as the sister-group to the clade Pseudotothyris plus Otothyris based on the following shared characters: elongated posterior extension of the compound pterotic, which forms the dorsal margin of an augmented lateral opening of the swimbladder capsule (char.8 of Schaefer, 1998); supraoccipital bone forming the dorsal wall of the swimbladder capsule (char.12), and the possession of enlarged odontodes on the snout margin (char.39).Otothyropsis marapoama, however, is distinguished from Pseudotothyris and Otothyris by having enlarged odontodes on the ventral and dorsal margins of the snout (vs.enlarged odontodes only on the dorsal snout margin), by the absence of conspicuous crests of enlarged odontodes on the supraoccipital and compound pterotics in adults, and by having the abdomen completely covered by dermal plates in adults.Ribeiro et al. (2005) described Otothyropsis based on three non-exclusive autapomorphies: possession of a single median rostral plate (char.34); possession of enlarged odontodes on the dorsal and ventral margins of the snout (char.39), and presence of an iris operculum (char.42).
During the last years we discovered four hypoptopomatine species, both in Brazil and Paraguay, with some degree of similarity and that partially fit the description of Otothyropsis.With the objective of testing these similarities and resolving a correct generic allocation for these species we conducted a phylogenetic re-analysis of the Hypoptopomatinae based on the data matrix of Schaefer (1998) with the modifications introduced by Ribeiro et al. (2005).Based on this re-analysis we describe one of these taxa recently collected in the rio Paraguay basin as a new species of Otothyropsis, re-diagnose the genus Otothyropsis and discuss its phylogenetic relationships.

Material and Methods
Measurements were obtained with digital calipers under a steromicroscope on the left side of specimens.Counts of rays and dentary and premaxillary teeth were also performed under the scope.Morphometric measures were treated as percents of the standard length (SL), except for subunits of the cephalic region, treated as percents of the head length (HL).Vertebral counts consider all vertebral centra, including the five centra modified into the Weberian Apparatus and the caudal complex centrum (PU1 + U1) was counted as a single element.The osteological examination was conducted in specimens cleared and stained according to the technique proposed by Taylor & van Dyke (1985).Dermal plate counts followed the method and terminology proposed by Schaefer (1997), and the morphometric measurements are those described by Pereira et al. (2007).Additional measurements are: pre-pelvic length (from the snout tip to the pelvic-fin origin), dorsal-fin base length (from the dorsal-fin origin to the end of the dorsal-fin base), internareal distance (horizontally between the inner margins of the posterior nares), and pre-nasal length (from the snout tip to the anterior margin of the anterior naris).
For the phylogenetic analysis we used the 46-character data matrix of Schaefer (1998) with the added characters 48 and 49 of Ribeiro et al. (2005).Thus, characters and character states mentioned in the text are those of Schaefer (1998) and Ribeiro et al. (2005), except when modifications were introduced, as described below (Table 1).The character 47 of Ribeiro et al. (2005) was excluded from our analyses because a large intraspecific variation was detected, precluding the identification of the fenestrae distribution pattern on the compound pterotic.In addition, the original codification of Ribeiro et al. (2005) for character states of Otothyropsis marapoama was changed as described below.Character 17: a subopercular plate between the opercle and the canalbearing plate is present in O. marapoama (state 0).Ribeiro et al. (2005) coded O. marapoama as absent for the subopercular plate (state 1), because they termed that plate as the canal plate 2. Character 29: the pectoral-fin spine possesses a fine serration on the median portion of its posterior margin (state 1).Character 32: the mid-dorsal series of lateral plates is truncated, ending midway between the dorsal and the caudal fin (state 1).Character 33: the median series of lateral plates is truncated posteriorly, and the last three plates of the dorsal and ventral series of lateral plates contact each other on the lateral midline anterior to the caudal fin (state 1).Character 35: rostral plate with a posterior notch on the area of articulation with the mesethmoid (state 1).Character 43: esophageal diverticulum is absent (state 0).Character 45: males of O. marapoama posses an expanded fleshy flap on the dorsal margin of the first pelvic-fin ray (state 0).
In addition to the characters of Schaefer (1998) and Ribeiro et al. (2005), we included the following one, numbered as character 47: extension of the sutures between neural spines.The neural spines between the dorsal-fin skeleton and the caudal fin of most hypoptopomines are sutured to each other from near the vertebral centra to approximately half the length of the neural spine (state 0).In the derived condition, found in Otothyropsis marapoama, O. piribebuy and the Otothyropsis sp. 3, the contiguous neural spines are sutured to each other from near the vertebral centra to or almost to their distal tips (Fig. 1; state 1).Hisonotus was found to be polymorphic to this character and was coded as missing (?).
We followed Schaefer (1998) in considering the characters 13, 24, 39, and 43 as additive.Contrary to Schaefer (1998), however, who used Neoplecostomus as the root, we rooted the trees in the compound outgroup LAH (Ancistrinae, Hypostominae, and Loricariinae of Schaefer, 1998), because we have strong evidence from Lehmann (2006) and Pereira (2008) that the Neoplecostominae represent the sister group to the Hypoptopomatinae.The phylogenetic analysis was performed with the software NONA 2.0 (Goloboff, 1999) on the Windows shell Winclada (Nixon, 1999).We used heuristic search with 1,000 replications of Random Addition Sequence (RAS) and branch swapping with Tree Bissection and Reconnection (TBR) plus a final round of TBR.Results are presented as a strict consensus tree.et al. (2005).

Results
The inclusion of four additional taxa in the data matrix of Schaefer (1998) and Ribeiro et al. (2005), resulted in six maximally parsimonious trees of 118 steps (CI = 0.50 and RI = 0.73).The strict consensus tree with the intergeneric relationships is presented in Fig. 2. The phylogenetic results corroborate the inclusion of all four new species in Otothyropsis, based on a new set of diagnostic characters, as presented below.Description.Proportional measurements and counts given in Tables 2 and 3, respectively.Dorsal body profile slightly arched from snout to origin of dorsal fin.Slightly concave and postero-ventrally oriented along dorsal-fin base, straight from terminus of dorsal-fin base to end of caudal peduncle and angling upward slightly immediately before caudal-fin origin.Ventral body profile Body entirely covered by dermal plates, except region around anus, region overlying lateral opening of swimbladder capsule, depression from nostril to rostral plates, area between pectoral girdle and lower lip, area around bases of paired fins, and scattered areas on anterior abdomen.Abdominal region covered with wide lateral abdominal plates laterally and with roundish to irregular, small platelets medially.Unplated areas usually present near the pectoral girdle and between lateral and medial patches of plates (Fig. 5) -one male in MCP 44394 with abdomen fully covered with plates.Ventral portions of cleithrum and coracoid completely exposed and supporting odontodes.Dorsal body surface with one slightly developed keel from posterior orbital margin to terminus of posterior extension of compound pterotic.Three transverse rows of predorsal plates, including nuchal plate.Median series of lateral plates with 19-20 plates.Lateral line with intermediate gap of 3-4 plates without sensory canal; last 3 plates without canal.Mid-dorsal series of lateral plates long and continuous, with 17-18 plates, ending 2-3 plates before the last plate in middle series.Rostral plates well developed and projected ventrally under snout margin.Odontodes on head and trunk pointed, strongly curved, uniform in size and distribution and not arranged into distinct rows.Odontodes on head not forming ridges.Odontodes on dorsal and ventral margins of snout much larger than surrounding ones.Fin rays covered by odontodes, larger on leading margin of all fins.Lips rounded and papillose, with small maxillary barbel laterally.Lower lip small, its posterior border approximately on vertical line passing through anterior margin or middle of eye.Teeth slender, bifid, with blade-like larger medial cusp and smaller lateral cusp.Contiguous neural spines suturally articulated to each other from vertebral centrum to or almost to dorsal end in adults.
Dorsal-fin II,7, its origin at vertical running close pelvicfin origin.Spinelet reduced, rounded and plate-like, and dorsalfin locking mechanism not functional.Adipose fin absent.Pectoral fin I,6, with posterior margin straight to slightly rounded.Tip of depressed pectoral fin extending to approximately end of pelvic-fin thickened first ray.Axillary slit of pectoral fin present, moderate in size and located below the lateral cleithral process.Pelvic fin i,5, short, with robust thickened first ray; posterior margin distinctly rounded.Tip of adpressed fin extending to anal-fin origin in males; reaching to anus in females.Adult males with fleshy flap along posterodorsal margin of thickened first pelvic-fin ray.Anal fin i,5.Caudal fin i,14,i.
Color in alcohol.Ground color of dorsal surface of head and body light to median brown, darker laterally on flanks; mostly unpigmented ventrally, except for light brown caudal peduncle and ventral portion of cheek and rostral plates.One sinuous light stripe from snout tip to each nostril, continuing as thin line through upper margin of orbit and compound pterotic.Two inconspicuous lighter stripes on each side of predorsal region and flanking dorsal fin.Fin membranes hyaline with dark brown chromatophores arranged in irregular transverse bands on rays.Caudal fin with four or five transverse bands of dark pigmentation, both on rays and membrane, stronger on base and lower lobe, sometimes imperceptible on upper.Bands on caudal-fin sometimes merging to form mostly dark lower lobe.One irregularly shaped, unpigmented area on middle of two or three lowermost branched rays usually conspicuous.Sexual dimorphism.Secondary sexual dimorphism in hypoptopomines is primarily characterized by the possession by males of an urogenital papilla, located immediately posterior to the anus, which is absent in females.Adult males also posses a fleshy flap along the dorsal margin of the thickened first pelvic-fin ray in most species, which is also absent in females.Otothyropsis piribebuy shares the two sexually dimorphic features above, and in addition has a longer first pelvic-fin ray, reaching to the origin of the anal fin (vs.shorter, never reaching to that point in females).Furthermore, O. piribebuy displays a remarkable secondary sexual dimorphism in the size of the naris opening, which is much bigger in males and affects most proportions of the head.Males have a smaller internareal distance (6.3-10.2 vs. 12.3-15.9%HL in females; Fig. 6), smaller prenasal length (28.9-32.9 vs. 31.6-36.4%HL in females), and larger orbital diameter (12.3-14.1 vs. 14.0-15.1% HL in females).Males also have a narrower body at the level of the dorsal-fin origin .

Distribution and habitat.
Otothyropsis piribebuy is known from two localities on the left tributaries to the río Paraguay, the río Piribebuy near Eusébio Ayala, Cordillera and the río Aguaray near Lima, San Pedro, Paraguay (Fig. 7).In both localities the fishes were collected on marginal vegetation, mainly formed by hanging grasses in the former and floating water-hyacinths (Eichornia) is the later.
Etymology.Otothyropsis piribebuy is named after the rio Piribebuy, rio Paraguay basin, where most type specimens were collected.In the native Guarany language "Piri vevui" means gentle breeze, a sensation caused by the many cool rivers in the region.A noun in apposition.

Table 2 .
Descriptive morphometrics of Otothyropsis species.Values are given for holotype and paratypes of O. piribebuy and O. marapoama.SD = Standard deviation.

Table 3 .
Frequency of distribution of meristic data for Otothyropsis piribebuy.Holotype values are marked with an asterisk.Meristic maked with double asterisks was counted in c&s specimens only.N = Number of specimens.