Xingu River Research Articles

Trends in climate extreme indices assessed in the Xingu river basin - Brazilian Amazon

The Xingu River Basin (XRB), located in the Brazilian Amazon, is of great importance both in national and international contexts, especially regarding hydroelectric generation in the Belo Monte Hydroelectric Complex and forest conservation policies, given that the XRB is home to important conservation areas, such as the Xingu Indigenous Park. This paper analyzes climate extreme indices in the XRB, a region that lacks this sort of information. Trends in 22 climate extreme indices were evaluated, 11 of them for air temperature and 11 for rainfall, based on spatially gridded and high resolution daily data, for the period from 1980 to 2016. The temperature indices showed significant upward trends in daily temperatures (both maximum and minimum), an indication that, in recent decades, the days and nights have become warmer in the XRB. For rainfall, the indices indicated a downward trend in the central and southern regions of the XRB (Middle and Upper Xingu), and increasing rainfall in the northern region of the basin (Lower Xingu), however, with lower statistical significance when compared to air temperature indices. Commonly, the areas that presented statistically significant trends in the assessed climate extreme indices correspond to areas where there have been alterations in land cover due to increasing use in recent decades (areas of forest that were modified for pasture and agriculture) and in areas still preserved. This paper is an important tool to support decision making in management and strategic planning of water resources (for power generation and multiple uses) and for the elaboration of forest conservation policies (for combatting and controlling deforestation) in the XRB, in times when the region is under constant pressure from agribusiness for the expansion of agriculture and livestock.

Taxonomic revision of Hopliancistrus Isbrücker & Nijssen, 1989 (Siluriformes, Loricariidae) with redescription of Hopliancistrus tricornis and description of four new species

Hopliancistrus is an Ancistrini genus diagnosed by having few and very strong cheek odontodes on interopercular area, and a patch of strong and stiff odontodes on the antero-lateral border of the snout. The type species is herein redescribed based on types and recently collected specimens. In addition, four new congeneric species are described based on specimens collected in other parts of the Rio Xingu and Rio Tapajós basins. Hopliancistrus tricornis is distributed in the lower Rio Tapajós and is diagnosed by the possession of four branched anal-fin rays and relatively large white to yellow spots on trunk and pectoral and pelvic fins, and dark brown spots on dorsal, caudal and anal fins. Hopliancistrus munduruku is described based on specimens from Rio Jamanxim (Rio Tapajós basin) and Rio Curuá (Rio Xingu basin) and is diagnosed by the possession of five branched anal-fin rays and large yellow blotches on trunk and dark brown to black spots over the fins. Hopliancistrus wolverine is distributed in the rapids of the lower and middle Rio Xingu and is diagnosed by the possession of five branched anal-fin rays and conspicuous small yellow dots on head, trunk and fins. Hopliancistrus xikrin is distributed in medium- to small-sized tributaries of the lower portion of Rio Xingu basin, and is diagnosed by absence of contact between the transverse process of the first dorsal-fin pterygiophore and the transverse process of the second pterygiophore. Hopliancistrus xavante is distributed in the tributaries of upper Rio Xingu basin, and is diagnosed by having a thick skin covering the nuchal plate; by having large white spots on trunk and fins; and by the possession of five branched anal-fin rays. An osteological description and a key for species identification are also provided.

Diversity of Loricariidae (Actinopterygii: Siluriformes) assemblages in two Conservation Areas of the Middle Xingu River, Brazilian Amazon, and their suitability for sustainable ornamental fisheries

Abstract The Xingu River has one of the most diverse fish faunas in the Amazon region. Loricariidae stands out as the most diverse family in the basin, comprising more than 60 species distributed over 26 genera. Species of Loricariidae are some of the most economically valued in the ornamental market worldwide. The loss of fishing environments in Altamira region due to dam impacts is driving a shift of ornamental fishing to areas upstream, among which are included the Xingu River and Iriri River Extractive Reserve Areas. Thus, the objective of this work was to inventory fish species with ornamental potential in these extractive reserves to serve as a baseline to help guide the future management of ornamental fishing in those areas. Thirty-two species of Loricariidae were collected in these reserves through either free diving or diving with compressed air. The composition of species varied according to the sampling method and area. The majority of species found in the reserves are also found in the impacted areas of Belo Monte near Altamira. The study areas showed high diversity of fish species in rapids environments, suggesting that this area could serve as an additional source of income for the residents of these reserves.

Mitochondrial DNA suggests Hybridization in Freshwater Stingrays Potamotrygon (POTAMOTRYGONIDAE: MYLIOBATIFORMES) from the Xingu river, Amazonia and reveals speciation in Paratrygon aireba

Abstract In the Xingu river basin, Brazil, occurs two genera of Potamotrygonidae family: Potamotrygon and Paratrygon. In this region, the taxa have significant economic importance for the ornamental fishing industry, being intensively captured, especially the species Potamotrygon leopoldi, which is endemic to this basin. In the attempt to propose a species-specific DNA marker for the species from Xingu, as well as ensuring a robust and reliable molecular identification, the present work analysed mitochondrial gene portions Cytochrome Oxidase C – subunit I (COI) and Cytochrome B (Cytb) of five species: P. leopoldi; Potamotrygon orbignyi; Potamotrygon motoro; Potamotrygon scobina and Paratrygon aiereba. We found haplotype sharing, with a total absence of reciprocal monophyly in the majority of taxa. Individuals morphologically identified as a species showed mitochondrial DNA from another, suggesting the first record of hybridization amongst freshwater stingrays of Xingu. Also, we detected a deep divergence among Paratrygon aiereba haplotypes, indicative of speciation, suggesting the possibility of a new species for the Xingu river. Therefore, although the is still confusing and controversial taxonomy of freshwater stingrays, and evidencing hybridization processes that may have shaped the evolutionary history of this Family, the genes COI and Cytb can successfully help in the their species identification.

Holocene diatoms from Xingu river: new records for the Brazilian Amazon and Brazil

ABSTRACT Present study is the floristic survey and the distribution of diatoms observed in two sediment cores of the Xingu river, Pará State, north Brazil, and represents the past ~6,000 cal yr BP. Thirty-eight taxa distributed in twenty genera were recorded, among which five were new records for Brazil and nineteen new for the Brazilian Amazon. The most representative genus based on species number was Gomphonema Ehrenberg with six species. In brief, present new records represent a 75% increase in the total number of records for the Brazilian Amazon, and indicates that this region has not only been poorly investigated, but also suggests that its biodiversity assessment is underestimated. These findings highlight the efficacy of the paleolimnological approach as a tool for assessing biodiversity before the human impacts begin to affect the pristine conditions of the area.

Occurence of Characidium xavante (Characiformes: Crenuchidae) in the Tapajós River basin and comments about the conservation status of the species.

Characidium xavante was described from two tributaries of the Culuene River drainage, in the upper Xingu River basin. New samplings recorded the species for streams from the Kaaiapó River drainage (Teles Pires River drainage, upper Tapajós River basin) with additional specimens also recorded in the Xingu River basin, Paranatinga municipality, Mato Grosso State, Brazil. The new records represent an extension of the geographical distribution of the species, that from now on fits in a pattern of distribution known to be shared with other ca. 20 species of fishes. We suggest that Characidium xavante could be classified as Least Concern (LC), according to the International Union for Conservation of Nature Standards and Petitions Committee (IUCN).

Saprophytic flies in impacted areas of the Belo Monte Dam, Pará, Brazil (Diptera: Mesembrinellidae, Neriidae, Ropalomeridae, and Sarcophagidae): community composition, abundance, and species richness

Abstract: The present study aims to document the community composition, abundance, and species richness of saprophytic fly species (Mesembrinellidae, Neriidae, Ropalomeridae, and Sarcophagidae) of the Volta Grande region of the Xingu River, a poorly sampled area impacted by the Belo Monte hydroelectric dam. Five collecting trips were carried out between 2014 and 2016, when traps baited with fermenting bananas were used. A total of 154 specimens, three genera, and six species were collected of Mesembrinellidae; 196 specimens, three genera, and seven species of Neriidae; 272 specimens, three genera, and six species of Ropalomeridae; and 624 specimens, 22 species and 10 genera of Sarcophagidae. Species accumulation curves for all families except Sarcophagidae demonstrated a strong tendency towards stabilization, showing that sampling efforts were sufficient to record most of the targeted species. Laneela perisi (Mariluis, 1987) (Mesembrinellidae) is a new record for the state of Pará. Among Ropalomeridae, Apophorhynchus amazonensisPrado, 1966, is a new record for Pará. Among Sarcophagidae, Helicobia aurescens (Townsend, 1927) is newly recorded from the Brazilian Amazon, and Ravinia effrenata (Walker, 1861) and Titanogrypa larvicida (Lopes, 1935) are new records for Pará.

Biometric and reproductive characteristics of the King Tiger Plecos Hypancistrus sp. “L-333” (Siluriformes: Loricariidae) endemic to the lower Xingu River (Pará, Brasil)

This research analyzed the biometrics and reproductive characteristics of a group of Hypancistrus sp. L-333 (King Tiger Plecos) in order to gather biological information and aid the rearing of the species in captivity, thus supporting its natural conservation. This species has a natural distribution that is restricted to the lower Xingu River, and is currently threatened by the hydroelectric projects in the region. The acquired specimens were measured, weighed and classified according to sex based on morphometric characteristics (evidence of secondary sexual characteristics) that were later confirmed by dissection. A total of 32 individuals, 16 males and 16 females were identified. Although the length-weight ratio did not present significant differences, the results revealed that the species has secondary sexual dimorphism. The odontodes were more developed in the mid-lateral region of the body, post-dorsal region, caudal peduncle and in the first ray (ossified) of the pectoral fin in males. Histological analyses of the gonads confirmed that all of the fish were adult individuals. The diameter of the oocytes ranged from 0.14 to 2.0 mm, presented three distinct modes, and were synchronous in more than two groups, which evidences batch spawning. Fecundity was low, between 35 and 54 oocytes in the largest batch. This information is novel and important for the identification of reproductive groups, and is aimed at breeding in captivity so that these resources can be exploited in a sustainable way, without harming the already threatened natural stocks.

Recent sedimentation in an Amazon tidal tributary: Integrated analysis of morphology and sedimentology

The Xingu River is an important tributary of the Amazon River, contributing 5% of its total water discharge. Nevertheless, it does not contribute substantially to the sediment load. The lower reach of the Xingu River forms a ria, a result of the Holocene sea-level rise. The Xingu is also classified as a tidal river, with tides >1 m at its confluence with the Amazon River. This study evaluated the morphology and sedimentology of the area, correlating both with hydrodynamics to understand the infilling process of the Xingu ria. The study area encompasses a stretch of ~160 km, between the Xingu–Amazon confluence and the narrowing of the fluvial channel. During the season of maximum sediment-discharge of the Amazon River (i.e., Feb 2016), 109 bottom sediment samples were collected. Eleven of the sampling sites were re-sampled during the minimum water-discharge period of both rivers (i.e., Nov 2016). During the maximum water-discharge period of the Amazon River (i.e., Jun 2018), additional water-level measurements were undertaken simultaneously at several locations along the Xingu River. The ria morphology was evaluated on the basis of the bathymetric surveys of the Brazilian Navy (DHN). The results show that the infilling process of the ria has taken place from both the upstream and downstream directions. From upstream, the Xingu River is forming a prominent bayhead delta. From the Xingu-Amazon River confluence, tides have transported Amazon River sediments into the Xingu Ria. There is a central portion of the ria lake with a large cross-sectional area, where relatively small amounts of muddy sediments are accumulating in a quiescent environment. Sands prevail along the lateral margins, where wave action causes bluff erosion and limits fine-sediment deposition. Sands are also common in the bayhead delta and the confluence areas. Results suggest that the sediment input from the Amazon River into the Xingu ria has been reduced over time, likely as result of a reduction in tidally driven flux from the Amazon River into the Xingu River, which has occurred with a gradual increase in the constriction of the confluence as Amazon floodplains prograde.

A new Planothidium species (Achnanthidiaceae, Bacillariophyceae) from Xingu Ria, Amazon River basin, Brazil

A new Planothidium species was found in sediment samples (~4,000 yr BP) from the Xingu Ria (Xingu River), Brazilian Amazon. The new species morphology was analyzed using light and scanning electron microscopy. Planothidium xinguense sp. nov., is mainly characterized by its elliptical, slightly asymmetrical valves, with strongly marked short rostrate ends in the small specimens, while long and strongly rostrate apices are observable in the larger valves. The taxon belongs to the group of species bearing a cavum on the rapheless valves around the name “Planothidium rostratum sensu lato”. Morphology and ecology of the new species is compared with that of morphologically related taxa. Information of core chronology and the co-occurrence of other diatom species in the sample is also provided.

Taxonomic review of the slender mouse opossums of the "Parvidens" group from Brazil (Didelphimorphia: Didelphidae: Marmosops), with description of a new species.

The genus Marmosops comprises small marsupials of the family Didelphidae (≤ 200 g), widely distributed in a variety of lowland rainforest and montane forest habitats, extending from Panama to southern Bolivia and southeastern Brazil. The smallest species of the genus are included in the "Parvidens" group, which includes M. pakaraimae, M. parvidens and M. pinheiroi. Although the monophyly of this group and species relationships are well defined, molecular studies have indicated that M. pinheiroi may represent a species complex, which has never been tested based on morphological analysis. In this study, we present the taxonomic review of M. pinheiroi based on the largest sample ever analyzed of this species. The external and craniodental morphology of 613 specimens of M. parvidens and M. pinheiroi from the northern, eastern, central and southern Brazilian Amazonia and northern Cerrado were examined. Besides, 28 craniodental dimensions were measured from adult specimens to support univariate and multivariate statistical analyses. Our results corroborate the validity of M. parvidens and indicate that M. pinheiroi is a complex formed by three species - M. pinheiroi (s. s.), distributed to the north of the Amazon River, from eastern Venezuela to the state of Amapá in Brazil; M. woodalli, which occurs east of the Xingu river and in the Marajó Island, state of Pará, extending to the east in the states of Tocantins and Maranhão; and a new species that occurs from the left bank of the Madeira River to the left bank of the Xingu River, herein described. Although the great morphometric similarity, species of the M. pinheiroi complex tended to be more different from each other than to M. parvidens in both univariate and multivariate analyses. Morphologically, these species may be positively distinguished by unique combinations of characters, such as dorsal and ventral fur coloration, arrangement of gray based hairs on the venter, supraoccipital shape, development of anterior and posterior portions of the M3 stylar shelf, continuity or not between the preprotocrista and anterior labial cingulum along the anterior margin of the upper molars, development of the metaconule in the upper molars, and number of cusps of the m4 talonid. The present work provides new perspectives for studies based on molecular data in order to test the species hypotheses recognized here and evaluate to what extent the Tapajós, Madeira, and Araguaia-Tocantins rivers actually isolate Marmosops populations.

Deciphering the many maps of the Xingu River Basin – an assessment of land cover classifications at multiple scales

Remote sensing is an invaluable tool to objectively illustrate the rapid decline in habitat extents worldwide. The many operational Earth Observation platforms provide options for the generation of land cover maps, each with unique characteristics and considerable semantic differences in the definition of classes. As a result, differences in baseline estimates are inevitable. Here we compare forest cover and surface water estimates over four time periods spanning three decades (1989–2018) for ∼1.3 million km2 encompassing the Xingu River Basin, Brazil, from published, freely accessible remotely sensed land cover classifications. While all showed a decrease in forest extent over time, the total deforested area reported by each ranged widely for all time periods. The greatest differences ranged from 9% to 17% (116,958 to 219,778 km2) deforestation of the total area for year 2000 and 2014–2018 time period, respectively. We also show the high sensitivity of forest fragmentation metrics (entropy and foreground area density) to data quality and spatial resolution, with cloud cover and sensor artefacts resulting in errors. Surface water classifications must be chosen carefully because sources differ greatly in location and mapped area of surface water. After operationalization of the Belo Monte dam complex, the large reservoirs are notably absent from several of the classifications illustrating land cover. Freshwater ecosystem health is influenced by the land cover surrounding water bodies (e.g., riparian zones). Understanding differences between the many remotely sensed baselines is fundamentally important to avoid information misuse, and to objectively choose the most appropriate classification for ecological studies, conservation, or policy making. The differences between the classifications examined here are not a failure of the technology, but due to different interpretations of ‘forest cover’ and characteristics of the input data (e.g., spatial resolution). Our findings demonstrate the importance of transparency in the generation of remotely sensed classifications and the need for users to familiarize themselves with the characteristics and limitations of each data set.

La producción del espacio social en la Amazonía brasileña a través de las represas hidroeléctricas: El caso del conflicto de Belo Monte

Durante las últimas décadas en Brasil se ha producido un incremento significativo de los conflictos hidrosociales a causa de la construcción de grandes complejos hidroeléctricos. Esta extensión de grandes proyectos de carácter extractivista en la región amazónica, sobre todo a partir de finales de la década de los años ochenta del siglo pasado, han conllevado todo un conjunto de transformaciones en las relaciones sociales, productivas y reproductivas, de cara avanzar en mecanismos para la integración regional y nacional, así como para la superación de crisis de acumulación propias de la escala global. Entre todos, por su trascendencia y dilatación en el tiempo, probablemente el que más destaca es el de la represa de Belo Monte en el río Xingú, próximo a la ciudad de Altamira. En él se ven involucrados una multiplicidad de actores (comunidades indígenas, campesinos, pescadores, el estado, Eletrobras, constructoras, instituciones supranacionales, etc) cuya disputa por el acceso a los recursos hídricos supone una modificación de la configuración de las relaciones de poder que se dan en el territorio. Este artículo, además de analizar el recorrido espacio-temporal de dicho conflicto, se propone dos objetivos adicionales. Por un lado la elaboración de un marco teórico, que conjugue las perspectivas de la producción de la naturaleza, la producción del espacio y la construcción de la escala, que pueda ser aplicado al análisis de conflictos ambientales que tienen lugar en el Sur Global. Por otro lado, y en consecuencia, a través de su empleo en el estudio de este caso particular, determinar las fortalezas y debilidades que presenta para su uso en futuros trabajos similares. De cara a ello se plantea una metodología basada en la revisión bibliográfica y el uso tanto de fuentes primarias como secundarias, mediante las cuales se puedan extraer y analizar el conjunto de prácticas, representaciones y relaciones que dan forma al conflicto en sí mismo. A su vez, el artículo se divide en cuatro partes principales: el planteamiento de articulación entre las distintas categorías y aspectos de los planteamientos teóricos para su uso en el estudio de caso; el análisis del desarrollo espacio-temporal del conflicto, desde el inicio de la planificación del proyecto hasta día de hoy; en tercer lugar se explica y detalla el papel de los actores hegemónicos en el avance de la construcción del complejo hidroeléctrico; y en última instancia se lleva a cabo la misma operación pero con los actores subalternos implicados. De entre los resultados obtenidos, destaca cómo este proyecto a nivel particular, y los macroproyectos hidroeléctricos en general en la región, han sido fundamentales para la integración económica en el marco de la extensión de las relaciones de producción capitalistas y los mecanismos para la acumulación a través de la realización del plusvalor, derivando resistencias ante este proceso de extracción. Así mismo, la perspectiva interescalar y la de la producción del espacio muestran potencialidades como marco para el estudio de conflictos ambientales, mientras que el de la producción de la naturaleza lo hace de manera parcial.

Effects of deforestation on water erosion rates in the Amazon region

Deforestation in the Amazon Rainforest is a recurring theme on the national and international environmental agenda. However, little attention has been given to its influence on water erosion and soil degradation. This study aimed to model the effect of deforestation on the spatial and temporal variation of water erosion in a watershed of the Amazon region. Therefore, we hypothesize that the expansion of deforestation, and the consequent changes in land use and cover, contributed to increasing soil losses due to water erosion. The Xingu River watershed was selected as a study area once it is one of the most affected regions by deforestation in the Brazilian Amazon. The estimate of water erosion was performed in the years 1988, 1998, 2008, and 2018 using the Potential Erosion Method (EPM). The application of the model was carried out in a Geographic Information System environment. Between 1988 and 2018, the deforestation in the selected basin increased by 12% (52,258 km2). In the same period, water erosion increased by 312%, corresponding to about 180 million tons of soil lost per year. The result of the study can help in planning erosion control in the Amazon region.

Island and Riverine populations of Alouatta belzebul from the Brazilian Amazon parasitized by Pediculus mjobergi.

Mammalian lice are obligate hematophagous ectoparasites that remain on the host throughout the life cycle. This study showed an endangered wild howler species (Alouatta belzebul) parasitized by Pediculus mjobergi. Twenty-seven primates were rescued during wildlife rescue activities in the process of vegetation suppression at the Belo Monte Hydroelectric Power Plant (UHE), located on the lower Xingu River, in the Brazilian Amazon basin. Among the 27 primates examined from two vegetal formations (alluvial rainforest and liana-infested forest) areas, 13 (48.15%) were parasitized by lice with all positive primates being from alluvial rainforest. Optical and scanning electron microscopy allowed the visualization of the structures and the diagnostic characters of the lice species in greater detail expanding the current description. These results highlight the importance of considering ecological and regional features to provide a better understanding of the factors that promote parasitism.

Dinâmica de uso e cobertura da terra no município de São Félix do Xingu, Estado do Pará, Brasil

As mudanças no uso e cobertura da terra são tidas como causadoras de grande degradação ambiental à medida que a floresta é convertida em outros usos. No Estado do Pará a principal atividade responsável pelo desmatamento é a pecuária, logo deve-se realizar estudos visando a identificação das mudanças no uso da terra devido a proteção do meio ambiente. Por esse motivo, o objetivo desse estudo foi analisar o desmatamento no município de São Felix do Xingu/Pará. Para o desenvolvimento do estudo foram utilizados dados fornecidos do Instituto Nacional de Pesquisas Espaciais – INPE que disponibiliza dados diários, mensais e anuais sobre os índices de desmatamento e degradação nas regiões brasileiras e quais atividades são exploradas. A partir disso, identificou-se que nos últimos anos a taxa de desmatamento só cresce de forma variável e rápida ao longo da temporalidade, sendo 54.167,5 km² de área devastada entre os anos de 2010 a 2019. Apenas em 2010 o território xinguense obteve 20,18% de destruição causada nas áreas florestais. Percebe-se que em 2015, os números saltaram para 21,23% comparado a 2010 e, assim os valores continuam maximizando em 2019 girando em torno de 22,88%. Com a análise temporal foi possível observar novas frentes de desmatamento que estão se dirigindo para Nordeste, Noroeste (paralelas ao rio Xingu) e Oeste (adentrando-se para a Terra do Meio). Logo, deve-se ter uma maior fiscalização por parte dos órgãos públicos nessas áreas, uma vez que a exploração ilegal e a pressão pelos recursos naturais estão aumentando com o passar dos anos.

Improving flood forecasting through feature selection by a genetic algorithm – experiments based on real data from an Amazon rainforest river

This paper addresses the problem of feature selection aiming to improve a flood forecasting model. The proposed model is carried out through a case study that uses 18 different time series of thirty-five years of hydrological data, forecasting the level of the Xingu River, in the Amazon rainforest in Brazil. We employ a Genetic Algorithm for the task of feature selection and exploit several different genetic parameters seeking to improve the accuracy of the prediction. The features selected by the Genetic Algorithm are used as input of a Linear Regression model that performs the forecasting. A statistical analysis verifies that the final model can predict the river level with high accuracy, which obtains a coefficient of determination equal to 0.988. Hence, the proposed Genetic Algorithm showed to be successful in selecting the most relevant features.

The genetic structure of Pristimantis latro (Anura: Craugastoridae) mirrors traits of their life history

One of the main hypotheses to explain the origin of Amazonian diversity is the barrier effect of the rivers known as the riverine-barrier hypothesis, which suggests that riverine barriers isolated once continuous populations leading to differentiation and speciation. In this context, we studied the genetic structure of Pristimantis latro, a newly described species that inhabits a region under marked anthropic pressure due to expansive livestock, illegal mining, and hydroelectric dam construction. The DNA was extracted from 52 P. latro individuals and then amplified via polymerase chain reaction (PCR) using the mitochondrial 16S rRNA and COI markers. To infer the time of divergence between the P. latro localities, we built a species tree and performed an analysis of molecular variance (AMOVA) to infer the genetic differentiation between and within the P. latro populations. We found that P. latro has a marked genetic structure in the populations of the right and left margins of the Xingu River and within the Tapajós-Xingu and Xingu-Tocantins interfluvial regions and that the time of divergence between the populations of the East and West banks of the Xingu River occurred approximately 380,000 years ago. This pattern of genetic structure corresponds to that reported in recent articles for the Pristimantis genus evidencing that species without tadpoles exhibit a genetic structure explained by the hypothesis of rivers as barriers.

An integrative approach assesses the intraspecific variations of Procamallanus (Spirocamallanus) inopinatus, a common parasite in Neotropical freshwater fishes, and the phylogenetic patterns of Camallanidae.

Integrative taxonomy was used to evaluate two component populations of Procamallanus (Spirocamallanus) inopinatus in Brazil and the phylogeny Camallanidae. Parasite populations were collected in the characiform Anostomoides passionis from River Xingu (Amazon basin) and Megaleporinus elongatus from River Miranda (Paraguay basin). Morphology was analysed using light and scanning electron microscopy (SEM). Genetic characterization was based on partial sequences of the 18S and 28S rDNA, and COI mtDNA. Phylogenies were based on 18S and COI due to data availability. Generalized Mixed Yule Coalescent (GMYC), Poisson Tree Process (PTP) and *BEAST were used for species delimitation and validation. SEM revealed for the first time the presence of minute denticles and pore-like structures surrounding the oral opening, phasmids in females and confirmed other important morphological aspects. Statistical comparison between the two-component populations indicated morphometric variations, especially among males. The different component population of P. (S.) inopinatus showed variable morphometry, but uniform morphology and were validated as conspecific by the GMYC, PTP and *BEAST. Some camallanid sequences in GenBank have incorrect taxonomic labelling. Host, environment and geographic aspects seem to be related to some lineages within Camallanidae; however, their real phylogenetic meanings are still unclear.

Systematics of Neotropical Spiny Mice, Genus Neacomys Thomas, 1900 (Rodentia: Cricetidae), from Southeastern Amazonia, with Descriptions of Three New Species

Species of Neacomys are small cricetid rodents that occur in forested habitats of Central and South America, from eastern Panama to central Bolivia and central/western Brazil. In order to assess species diversity of this poorly known genus, we obtained cytochrome b gene sequences from the most comprehensive taxonomic and geographic sampling analyzed to date. We also conducted morphological analyses on a large series of specimens housed in 15 museums, including types of 10 out of 14 nominal taxa. Our analyses of the genetic data recovered 17 lineages clustered in four distinct clades. Among these lineages, 11 correspond to species currently recognized as valid, and the remaining six are putative new species. In southeastern Amazonia—the geographical scope of this report—four undescribed species were discovered, three of which are named herein: Neacomys marajoara, sp. nov., from the Island of Marajo, Para state; Neacomys vossi, sp. nov., restricted to the Tapajos center of endemism (between the Tapajos and Xingu rivers); and Neacomys xingu, sp. nov., restricted to the Xingu center of endemism (between the Xingu and Araguaia/Tocantins rivers). The new species can be discriminated from other Neacomys species by the morphology of the nasal bones, zygomatic plate, interorbital region, subsquamosal fenestra, paraoccipital process, incisive foramina, auditory bullae, anterocone and anteroloph of the first upper molar, carotid circulation pattern, and karyotype. Our results substantially improve our understanding of the genus Neacomys by providing morphological, morphometric, and novel molecular insights about these poorly known rodents and demonstrate that the diversity of small Amazonian mammals is still poorly known, even in the relatively accessible southeastern part of the biome.