Hemiodus langeanii ( Characiformes : Hemiodontidae ) , a new species from rio Amana , rio Maués-Açú drainage , Amazon basin , Brazil

Hemiodus langeanii, new species, is described based on 20 specimens collected in the rio Amana, a tributary of rio MauésAçú, rio Amazonas drainage, Brazil. The new taxon can be distinguished from its congeners by its high body (27.1-35.3%, average 32.3% SL vs. 18.8-28.5% in remaining species). The new species also exhibits a large lateral dark spot that is equal to, or greater than, the eye diameter (vs. smaller in remaining species except for H. microlepis). The lack of conspicuous lateral stripe or transverse bands and the low lateral line scales count (68-74) distinguish H. langeanii from some similar species in the genus (scale counts: 94-123 in H. argenteus, 124-148 in H. microlepis, 86-99 in H. orthonops and 77-92 in H . parnaguae). Finally, the new species can be differentiated from H. unimaculatus (which overlaps in the number of lateral line scales) by the higher number of scales between the lateral line and the pelvic fin origin (9-10 vs. 4-7, respectively), which are similar sized above and below lateral line (vs. scales larger bellow the lateral line in H. unimaculatus).


Introduction
The genus Hemiodus Müller, 1842 includes small to medium sized fishes (7-30 cm of standard length) that occur in the Amazon, Orinoco, Araguaia-Tocantins, Essequibo, Paraná-Paraguay and Parnaíba river basins (Langeani, 2003).The most recent revision of the genus was by Langeani (1996), which was followed by the description of only two new species, Hemiodus tocantinensis Langeani, 1999 andH. jatuarana Langeani, 2004.The species of Hemiodus share only one synapomorphy: medial surface of preopercle with a small ventrally angled depression, which receives the posteroventral portion of the hyomandibular (Langeani, 1998); in addition, they are also diagnosed by having small multicuspidated teeth in the upper jaw, and edentulous lower jaw.
There is no comprehensive phylogenetic study of the relationships between the species of Hemiodus.Nevertheless, Langeani (1996) divided Hemiodus in two artificial groups: a) species with more than 80 lateral line scales, and b) species with less than 80 scales along the lateral line.At present, 19 species are recognized in the genus, in addition to four undescribed species from the Amazon River basin (Langeani, 2003(Langeani, , 2004)).Hemiodus species show some variation in general color pattern, however most species exhibit a round lateral dark spot and a short dark stripe along the lower lobe of caudal fin.
During an ichthyofaunal survey conducted in the Floresta Nacional do Amana reserve (FLONA do Amana) near the boundary between States of Pará and Amazonas in Brazilian Amazon we collected specimens of a species of Hemiodus with the typical dark lateral spot pattern, but exhibiting a conspicuous high body depth and low lateral line scale counts, which is described herein as new.

Material and Methods
Morphometric and meristic data were obtained following Langeani (1999).All morphological measurements were made with a digital caliper and expressed as proportions of standard length (SL) or head length (HL) (Table 1).Counts include lateral line (LL) scales, scales below LL to pelvic-fin origin and above LL to dorsal-fin origin, circumpeduncular and postdorsal (between dorsal and adipose fins) scales, fin rays, gill rakers on first branchial arch, branchiostegal rays, and upper jaw teeth.Whenever possible, measurements and counts were performed on the left side of specimens.In the description, counts are followed by their frequency in parentheses, with asterisks indicating the holotype.Vertebrae of the Weberian apparatus were counted as four elements and the fused PU1+U1 of the caudal region as a single element.Counts of vertebrae, gill rakers on the first branchial arch, tooth cusps, and premaxillary teeth were taken from cleared and stained specimens (c&s) prepared according to Taylor & van Dyke (1985).In the list of material examined, the total number of specimens is followed by the number of those cleared and stained (if any).Specimens were deposited at the Fish Collection of Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Amazonas; Museu Paraense Emílio Goeldi (MPEG), Belém, Pará and at Museu de Zoologia da Universidade de São Paulo (MZUSP), São Paulo, Brazil.1903, andH. parnaguae Eigenmann &Henn, 1916 that have values that fall within the limits of variation of new species).

Color in life.
Overall body color silvery with dorsum darker.Eyes yellowish with dark chromatophores forming a bar, darker at upper portion of eye.All fins orange tinted.Caudal fin orange, darker in distal portion and with coloration more evident on lower lobe.Black longitudinal stripe along each caudal lobe, with stripe of lower lobe darker (Fig. 2).

Color in alcohol.
Overall body color pale brown to yellowish.Lateral spot black and connected to dark stripe of lower caudal lobe by inconspicuous dark midlateral band; in some specimens lateral band extending forward to dorsal portion of operculum.Upper portion of body side with 36 to 39 narrow vertically arranged V-shaped lines (chevrons).Pectoral and pelvic fins hyaline.Dorsal and anal fins with dark chromatophores almost to distal tips.Adipose fin with dark base and light distal edge.Eye with conspicuous bar passing through pupil.
Distribution.Known of the type locality in the rio Amana, rio Maués-Açu drainage, near the boundary of the States of Pará and Amazonas, Brazil (Fig. 3).
Ecological notes.Specimens of Hemiodus langeanii were caught in slow-flowing stretches of the rio Amana and igarapé Porquinho (1.0-2.5 m deep) and in artificial ponds (4.0-5.0 m deep and 40-70 m in diameter) resulting from goldmining activities.The rio Amana and its tributaries have clear water (not stained by humic acids) but turbid due to excess of fine suspended solids (clay) resulting from mining activities along river margins and/or bottom (dredging).Water at the collecting sites was turbid (vertical transparency 10-21 cm), slightly acidic (pH 6.4-6.8) with a temperature of 25.5-27.7ºC;dissolved oxygen of 6.5-7.3 mg/ L and 80-92% of saturation (measurements made between 9:00-11:00 am).Observations of living individuals of  Hemiodus langeanii in its habitat revealed that the new species shows benthopelagic habits and was often caught with other characiforms such as Pseudanos sp., Hoplias malabaricus (Bloch, 1794), Myloplus sp. and Serrasalmus eigenmanni (Norman, 1929).
Popular names.In the Brazilian Amazon, species of the genus Hemiodus are referred to as Orana, Cubio, Charuto, and Flecheiro.
Etymology.Named in honour of Dr. Francisco Langeani (researcher at Instituto de Biociências, Letras e Ciências Exatas -Universidade Estadual Paulista "Júlio de Mesquita Filho"-UNESP, Brazil), for his highly relevant contributions to the knowledge of hemiodontid fishes.

Discussion
The new species presented herein was included in the genus Hemiodus based on the definition and morphological characters used by Langeani (1996).Following the artificial groups within the genus proposed by Langeani (1996), the new species is included among congeners with less than 80 perforated scales on the lateral line, which comprise 15 valid species (Langeani, 1996(Langeani, , 1998(Langeani, , 1999(Langeani, , 2003(Langeani, , 2004) and an additional possibly new form (J. Zuanon, pers.obs.).
Hemiodus langeanii lacks a conspicuous longitudinal stripe along the body or transverse bands of melanophores.The lack of such pigmentary features clearly diagnoses the new species from, on one hand, H. thayeria, H. ternetzi, and H. tocantinensis, all showing a conspicuous longitudinal stripe which extends from the distal border of operculum to the caudal fin base; and from H. quadrimaculatus, H. vorderwinckleri, H. huraulti, and H. sterni; all of which present transverse dark bands on body side.The new species can be distinguished from H. goeldii, H. atranalis, H. gracilis, and H. semitaeniatus by lacking the conspicuous longitudinal stripe extending from the lateral spot to the caudal fin base, characteristic of the latter species.The color pattern of H. langeanii also allows to distinguish it from H. immaculatus (lateral spot absent) and H. jatuarana (with a dark spot at caudal peduncle).Among the Hemiodus species with fewer than 80 lateral line scales, H. unimaculatus and H. amazonum are the most similar to H. langeanii, both regarding to body shape as well as color pattern (i.e., a rounded lateral blotch on the flank and a dark stripe at lower caudal lobe).Nevertheless, H. langeanii differs from H. amazonum by the higher number of lateral line scales (68-74 vs. 51-60, respectively) and from H. unimaculatus (which overlaps the new species in lateral line scales counts) by the presence of 9-10 transverse rows of scales below LL (vs.4-7 transverse rows of scales below LL), and for having body scales similarly sized (vs.scales on body below LL distinctly larger than those above LL) (Table 2).Other congeneric species such as H. argenteus, H. microlepis, H. orthonops, and H. parnaguae also show a very similar color pattern and body height to that found in the new species, but differ from it mainly due to higher LL scales counts (77-148 vs. 68-74 in H. langeanii; Table 2).Finally, the new species has a high body depth (mean 32.5% SL), which is higher than in other tall-bodied congenerics Table 2. Lateral Line and transverse series scales counting in Hemiodus langeanii and in congeneric species with a similar colour pattern (n = number of analyzed specimens); meristic data extracted from Langeani (1996).such as H. microlepis and H. argenteus (28.6 and 26.3% SL, respectively; Langeani, 1996), and distinctly higher than H. unimaculatus (mean 25.6% SL) (Fig. 4).
Hemiodus species are generally widespread, common fishes often exploited by artisanal and commercial fisheries and ornamental fish trade in the Brazilian Amazon (Ferreira et al., 1998;Ruffino et al., 2005;2006;Beltrão et al., 2009).Hemiodus langeanii, however, is known so far only from rio Amana and some of its small tributaries upstream from a main waterfall (10-12m high) in the river course.Although we have sampled several aquatic environments associated to the rio Amana inside the FLONA do Amana, as well as other water courses nearby, it was not possible to register the occurrence of the new species beyond the type locality.The waterfall in the rio Amana possibly represents a natural barrier for this species, but more intensive collecting efforts are necessary to determine if the new taxon is truly endemic to the rio Amana basin.
Hemiodus langeanii apparently has a low abundance in the sampled habitats, which include artificial lakes resulting from goldmining activities, as well as the rio Amana and its small tributaries, which already have signs of strong anthropogenic disturbances (Fig. 5).Therefore, the conservation status of the new species, although uncertain, already gives some causes for concern.The high content of suspended colloidal clay and the large sand and mud deposits carried to the bottom of the river and streams may result in siltation and further decrease of the water transparency, which can put in risk the survival of the new species.

Fig. 4 .Fig. 5 .
Fig. 4. Body height as a function of the standard length in Hemiodus langeanii n. sp.compared to H. argenteus and H. unimaculatus.

langeanii, new species Figs. 1a, 2 Holotype. INPA
, H. gracilis Günther, 1864, H. semitaeniatusKner, 1858, H. immaculatus Kner, 1858 and  H. jatuarana Langeani, 2004).Hemiodus langeanii differs from most similar species (H.unimaculatus (Bloch, 1794), H. amazonum (Humboldt, 1821), H. argenteus, H. microlepis, H. orthonops and H. parnaguae), with a rounded lateral blotch on the flank and a dark stripe at lower caudal lobe), by its large dark lateral spot equal to, or greater than, the eye diameter (vs.smaller in remaining species except for H. microlepis) and lateral line scale counts68-74 (vs.94-123 in H. argenteus, 124-148 in H. microlepis, 86-99 in H. orthonops,  77-92 in H. parnaguae, and 51-60 in H. amazonum ).Finally, H. langeanii differs from H. unimaculatus (which overlaps in lateral line scale counts) by a higher number of scales between the lateral line and the pelvic-fin origin (9-10), with scales of similar sizes above and below the lateral line (vs.4-7, with scales below lateral line larger than those above it in H. unimaculatus).Description.Morphometrics and meristics in Table1.Largest examined specimen 133.3 mm SL.Body relatively short, deep and slightly compressed laterally.Highest body depth at dorsal fin origin.Dorsal profile of body convex to adipose fin and slightly concave from that point to anteriormost dorsal procurrent caudal fin ray.Ventral body profile slanted from snout to origin of pectoral fin, strongly convex from that point to anal-fin, slightly concave between that point to anteriormost ventral procurrent caudal fin ray.Interorbital region slightly concave and greater than snout lenght.Mouth subterminal, not protractile, with

Table 1 .
Morphometrics and meristics of Hemiodus langeanii n. sp., expressed as percent of standard length (SL) or head length (HL).SD = standard deviation.