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ECOSYSTEMS • An. Acad. Bras. Ciênc. 98 (3) • 2026 • https://doi.org/10.1590/0001-3765202620251315 linkcopy

Open-access List of Ranatra Species (Heteroptera: Nepomorpha) from the tributaries of the Xingu River in the Brazilian Amazon

AuthorshipSCIMAGO INSTITUTIONS RANKINGS

Abstract

Areas of endemism are geographic units characterized by unique biological diversity and evolutionary histories, enabling the formulation of hypotheses about the processes shaping regional ecosystems. Aquatic insects are essential components of freshwater environments, and the genus Ranatra Fabricius, 1790 is commonly found in slow-flowing streams rich in leaf litter and submerged roots. Known as “water scorpions”, 35 species have been reported across Brazil to date. Despite growing research efforts, substantial gaps remain regarding the diversity of these insects, particularly in terms of species identity (Linnean shortfall) and distribution (Wallacean shortfall). In this study, we present a species list of Ranatra Fabricius, 1790 from streams of the Xingu Basin, Pará State, a region located within the Tapajós and Xingu Areas of Endemism in the Brazilian Amazon. We sampled 165 individuals belonging to 13 species, including three new distributional records for the state of Pará, R. brasiliensis De Carlo, 1946, R. doesburgi De Carlo, 1963, and R. rabida White, 1879. Our findings emphasize the importance of expanding research and monitoring efforts in freshwater systems, particularly in highly diverse regions increasingly threatened by anthropogenic pressures and climate change, such as those of the Amazon biome.

Key words
Aquatic Hemiptera; Amazonian biodiversity; Areas of Endemism; Spatial Distribution; Range Expansion; Stream Ecosystem Monitoring

INTRODUCTION

The Amazon Rainforest is the most diverse ecosystem in the world, comprising approximately 10% of all recorded biodiversity (Jung et al. 2021). However, its true diversity may be much higher, as many groups, particularly insects, remain neglected and underestimated. Moreover, the Amazon is not a homogeneous system, it contains numerous areas of unique diversity, largely due to broad environmental variation and major dispersal barriers created by the region’s large rivers (Juen & De Marco 2012, Ribas et al. 2025). This diversity is often composed of species with extremely restricted distributions, recorded from few locations and forming unique biotas (Castro et al. 2020). These regions are known as areas or centers of endemism, characterized by their own biota and evolutionary histories, and serving as key geographic units for biodiversity and historical biogeographic analyses, forming one of the main bases for hypotheses about the processes shaping regional biotas (Da Silva et al. 2005).

The Amazon is composed of eight areas of endemism: Guiana, Imeri, Napo, Inambari, Rondônia, Tapajós, Belém, and Xingu. Of these areas, three are entirely within Brazilian territory (Belém, Xingu and Tapajós), the latter two are located within the tributaries of the Xingu River, which is connected to the Amazon River (Almeida et al. 2014). A large part of this region lies within the deforestation arc, where large portions of pristine vegetation are cleared and removed for anthropogenic land conversion, representing a progressive structural modification filter affecting streams and aquatic communities within it (Castro et al. 2020, Cavalcante et al. 2024).

For species to persist in a given environment, they depend on highly specific environmental conditions, and any modification of these conditions typically leads to decreased abundances, and depending on the intensity, even to local extinction (Dias-Silva et al. 2010, Ribeiro et al. 2022). Anthropogenic and climatic disturbances alter environmental conditions with highly negative consequences for biodiversity. However, due to biodiversity knowledge gaps, our understanding of most species remains limited, and many groups still lack basic information regarding species identity, known as the Linnaean shortfall, and the extent of their geographic distributions, known as the Wallacean shortfall, a problem that is even more severe for insect groups (Whittaker et al. 2005, Bini et al. 2006). In addition, current knowledge is concentrated in a few accessible regions, while remote areas remain largely understudied. A recent study demonstrated that knowledge of aquatic insects in the Amazon is still highly limited, particularly in remote regions such as those found within the tributaries of the Xingu River (Carvalho et al. 2023).

The impacts of environmental change are even more intense in fragile and sensitive systems, such as aquatic environments, especially the small streams. In these ecosystems, alterations occurring in the drainage basin are transmitted directly into the channel, destabilizing the banks, reducing canopy cover, increasing the input of contaminants and sediments, decreasing natural variability, and consequently reducing habitat diversity (Juen et al. 2016). In such streams, aquatic insects can be found, and they are essential for nutrient cycling and energy transfer within food webs, they exhibit high species diversity and are strongly dependent on local environmental conditions (Hamada et al. 2014). An important group within aquatic insects is the benthic Nepomorpha, characterized by having “hidden antennae”, since these are inserted below the eyes, and most organisms in this infraorder are ambush predators (Nieser & Melo 1997). This infraorder comprises 10 families, 32 genera, and approximately 292 species recorded for Brazil (Moreira et al. 2011, Damasceno Durval et al. 2024). To this date, about 24 species have been recorded for the Amazon region.

In this infraorder, the genus Ranatra Fabricius, 1790 (Nepidae) is commonly known as water stick insect or water scorpion. These predators prefer low-flow habitats within lotic environments, anchoring themselves along stream margins and camouflaging among riparian roots (Nieser 1975, Polhemus & Polhemus 2008). They use a sit-and-wait predation strategy and feed on fish and other arthropods. They show high environmental sensitivity and are considered bioindicators of the habitat quality (Bakonyi et al. 2022). Currently, 35 species are recorded for Brazil, and although they are relatively simple to identify, there are few studies addressing their taxonomy and distribution (Moreira et al. 2011, Damasceno Durval et al. 2024, De Lima et al. 2026).

Studies aimed at identifying species and understanding their spatial distribution, especially in understudied regions such as the Amazon, are essential for reducing the Linnean and Wallacean shortfalls (Bini et al. 2006, Cardoso et al. 2011, Hortal et al. 2015). In this context, and considering the scarcity of information on the genus Ranatra in the Amazon, our study aimed to present a species list of Ranatra Fabricius, 1790 in the tributaries of the Xingu Basinin the state of Pará within the Tapajós and Xingu centers of endemism as well as update the distribution records of the species for Brazil.

MATERIALS AND METHODS

Study area

The study covers the tributaries of the Xingu River, focusing on lotic systems, such as streams. These are located in two areas of endemism: Xingu, with an area of endemism covering 392,468.517 km² in 88 municipalities, mainly in the state of Pará; and Tapajós, with approximately 656,150.10 km² in 56 municipalities, 17 of which are located in the state of Pará (Almeida et al. 2014, Escada et al. 2014, Oliveira et al. 2017). These streams occur within the three most deforested areas of endemism, surpassed only by the Belém area. In fact, approximately 70% of these regions lie within the deforestation arc, where intense anthropogenic pressures drive substantial alterations in natural aquatic environments (Braz et al. 2016, Castro et al. 2020).

The region is characterized as having an “Am” tropical climate, hot and humid according to the Köppen classification, with a mean temperature of 26.1°C and an average annual rainfall of 1914 mm (Climate-Data 2020). In this region, the months with the highest precipitation occur from February to May, while the driest months extend from August to October. Over the past decades, activities such as cacao cultivation and cattle ranching have intensified, especially after 2006, generating deforestation and altering local habitat structure, in addition to the removal of riparian vegetation along many stream sections (Dos Santos & Da Silva 2017, Cavalcante et al. 2024).

These alterations directly affect aquatic organisms inhabiting streams, preventing their full development, reproduction, and feeding (Juen et al. 2016). These systems are highly sensitive to environmental changes, highlighting their fragility and the need for conservation. Therefore, the sampling was conducted in 33 streams between August and October from 2019 to 2024. These streams are distributed across the municipalities of Altamira, Anapu, Senador José Porfírio, Vitória do Xingu, and Medicilândia, in the state of Pará, within the tributaries of the Xingu River (Figure 1).

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Figure 1
Distribution map of the sampled rivers in the tributaries of the Xingu River.

Sampling collection

In each stream, the sampling was carried out along a fixed 100-meter stretch, which was later divided into 20 segments of five meters each, to increase sampling efficiency (Figure 2) (Dias-Silva et al. 2010). In each segment, a hand net with an 18 cm diameter and 0.50 mm mesh was used, sweeping from the bottom toward the margin to sample all available substrates, especially the roots of trees and macrophytes (Figure 3). The pre-sorted material was taken to the Laboratory of Ecology and Conservation (LABECO) at the Federal University of Pará, Altamira campus, where it was stored in 70% ethanol.

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Figure 2
Illustrative figure of the 100-meter sampling method carried out in each stream.
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Figure 3
Sampling of biological material. a) Collection in segments using the hand net, b) Storage in transparent bags, c) Pre-sorting in the field.

Species identification

Identification at the genus and species levels followed specialized keys for the infraorder Nepomorpha. We used the keys of De Carlo (1972), Nieser (1975), Nieser & Melo (1997), and consulted the original species descriptions by De Carlo (1964, 1970) and Kuitert (1949). Specimens were examined under a Zeiss Stemi 305 stereomicroscope. Key characters included the presence or absence of an interocular tubercle, body and siphon length in millimeters, male genitalia with parameters dissected using a no. 15 scalpel blade, and the number of post-abdominal teeth in females. Each Falcon tube containing a single species was labeled with the collection site, date, identifier name, and the catalog number.

Compile occurrence data

In addition to primary data, we compiled the secondary occurrence records from the literature and online collections for all Ranatra species recorded in the region. The databases consulted included the Global Biodiversity Information Facility (GBIF), SpeciesLink (SPLIN), the Taxonomic Catalogue of the Brazilian Fauna (CTFB), and the Integrated Taxonomic Information System (ITIS) (CTFB 2015, GBIF 2024, SpeciesLink 2024, ITIS 2024). The distribution maps were generated in QGIS version 3.36.2.

RESULTS

A total of 163 adult Ranatra individuals were identified, distributed among 13 species, with Ranatra macrophthalma Herrich-Schäffer, 1849 being the most abundant (n = 39). Other abundant species included Ranatra mixta Montandon, 1907 (n = 20), Ranatra magna Kuitert, 1949 (n = 18), Ranatra doesburgi De Carlo, 1963 (n = 17), and Ranatra tuberculifrons Montandon, 1907 (n = 12) (Table I).

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Table I
List of Ranatra species (Heteroptera: Nepomorpha) from the tributaries of the Xingu River.

Species currently recorded in Pará

! New occurrence records in Brazilian states.

? Occurrence with imprecise or state-level estimated location.

Family. Nepidae Latreille, 1802.

Genus. Ranatra Fabricius, 1790.

Ranatra adelomorpha Nieser, 1975

Figure 4 A/Figure 5 (a-c)/Figure 9 (a).

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Figure 4
Distribution map of the species Ranatra Fabricius, 1790, across Brazilian states: a) shows the distribution of the species R. adelomorpha, R. brasiliensis, R. doesburgi, and R. macrophthalma; b) shows the distribution of the species R. magna, R. mediana, R. mixta, and R. moderata; c) shows the distribution of R. parvula, R. rabida, and R. tuberculifrons, and d) shows the distribution of R. obscrura.
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Figure 5
Images of Ranatra Fabricius, 1790 species. Ranatra adelomorpha (a) dorsal view of female, (b) ventral view of female, (c) interocular space of female; Ranatra brasiliensis (d) dorsal view of male, (e) ventral view of male, (f) interocular space of male; Ranatra doesburgi (g) dorsal view of female, (h) ventral view of female, (i) dorsal view of male, (j) ventral view of male, (k) interocular space of female; Ranatra macrophthalma (l) dorsal view of female, (m) ventral view of female, (n) dorsal view of male, (o) ventral view of male, (p) interocular space of female.
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Figure 9
Images of female opercula. (a) Ranatra adelomorpha, (b) Ranatra doesburgi, (c) Ranatra macrophthalma, (d) Ranatra magna, (e) Ranatra mediana, (f) Ranatra mixta, (g) Ranatra moderata, (h) Ranatra parvula, (i) Ranatra tuberculifrons.

Distribution in Brazil: PA (De Lima et al. 2026; This study).

Taxonomic comments: The individuals have body lengths ranging from 27 to 33 mm (♀ 33 mm, ♂ 27–29 mm), and the respiratory siphon is shorter than the body, ranging from 21 to 25 mm (Nieser 1975).

Comments:R. adelomorpha represents the second recorded occurrence in Brazil.

Examined material: IG04 (-3,297310; -52,413950), (2♀), [n°60], 25.IX.2019. IG11 (-3,407750; -52,735600), (1♀), [n°42], 17.IX.2020. IG14 (-3,141980; -52,269090), (1♀), [n°41], 17.IX.2020. IG22 (-3,154167; -52,154333), (1♀), [n°40], 30.X.2021. IG33 (-3,387997; -52,143997), (1♀), [n°327], 19.XI.2023. IG02 (-3,025183; -51,722417), (2♀), [n°633], 24.IX.2019. IG02 (-3,025183; -51,722417), (1♀), [n°663], 24.IX.2019.

Ranatra brasiliensis De Carlo, 1946

Figure 4 A/Figure 5 (d-f)/Figure 10 (a).

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Figure 10
Image of male parameres of Ranatra. (a) Ranatra brasiliensis, (b) Ranatra doesburgi, (c) Ranatra macrophthalma, (d) Ranatra magna, (e) Ranatra mediana, (f) Ranatra mixta, (g) Ranatra moderata, (h) Ranatra obscura, (i) Ranatra rabida, (j) Ranatra tuberculifrons, (k) Ranatra sp. 1.

Distribution in Brazil: AM?, PA! (De Carlo 1946, Nieser 1975, This study).

Taxonomic comments:R. brasiliensis is similar to R. mediana, differing in body size, since R. brasiliensis is larger, measuring about 35 mm, while R. mediana ranges from 29 to 32 mm, and also in the shape of the male paramere (Nieser 1975).

Comments: This species represents an expansion of its known occurrence into the state of Pará. In De Carlo’s 1946 study, the distribution listed for this species is “Maná” in Brazil, which may refer to the Maná River in the Amazonas state. Although the locality is uncertain.

Examined material: IG22 (-3,154167; -52,154333), (1♂), [n°48], 30.X.2021. IG22 (-3,154167; -52,154333), (1♂), [n°49], 30.X.2021. IG23 (-3,434917; -51,621250), (1♀), [n°644], 13.IX.2019.

Ranatra doesburgi De Carlo, 1963

Figure 4 A/Figure 5 (g-k)/Figure 9 (b)/Figure 10 (b).

Distribution in Brazil: AM?, PA! (Nieser 1975, This study).

Taxonomic comments: Females have approximately six dorsal teeth on the operculum, which are visible beyond the end of the abdomen, and males lack the subapical tooth on the paramere (Nieser 1975). Female body size ranges from 34 to 35 mm with siphons measuring 25 mm, and males have body lengths of about 31 mm with siphons of 22–23 mm (De Carlo 1964).

Comments: In Nieser’s 1975 work, R. doesburgi was recorded only for the state of Amazonas, and the other examined specimens were listed as paratypes of R. usingeri. This occurred because R. usingeri was, at the time, synonymized with R. doesburgi by Nieser. Therefore, this species represents an expansion of its known distribution into the state of Pará.

Examined material: IG07 (-3,323150; -52,265870), (1♂), [n°46], 04.X.2020. IG14 (-3,141980, -52,269090), (1♂), [n°47], 17.IX.2020. IG09 (-3,359360; -52,288170), (1♂), [n°53], 07.X.2020. IG30 (-3,322997; -52,265997), (2♀), [n°385], 17.XI.2023. IG21 (-3,320510; -52,331320), (1♂), [n°386], 19.X.2023. IG21 (-3,320510; -52,331320), (1♂), [n°387], 19.X.2023. IG21 (-3,320510; -52,331320), (1♂), [n°388], 19.X.2023. IG21 (-3,320510; -52,331320), (1♂), [n°389],19.X.2023. IG21 (-3,320510; -52,331320), (2♂), [n°390], 19.X.2023. IG14 (-3,141980, -52,269090), (1♂), [n°660], 17.IX.2020. IG23 (-3,434917; -51,621250), (1♂), [n°632], 13.IX.2019. IG02 (-3,025183; -51,722417), (1♀), [n°659], 24.IX.2019. IG19 (-3,280067; -52,862883), (1♂), [n°725], 08.IX.2024. IG19, (1♀), [n°726], 08.IX.2024.

Ranatra macrophthalma Herrich-Schäffer, 1849

Figure 4 A/Figure 5 (l-p)/Figure 9 (c)/Figure 10 (c).

Distribution in Brazil: AM, PA (Nieser 1975, Cunha et al. 2015, De Lima et al. 2026, This study).

Taxonomic comments: Individuals of this species have pale legs with well-defined stripes. Body length ranges from 39 to 42 mm, and the respiratory siphon is equal to or shorter than the body length. In females, the operculum clearly extends beyond the tip of the abdomen (Nieser 1975).

Comments: This was the most common species in the streams of the studied region.

Examined material: IG13 (-3,470820; -52,744640), (1♂), [n°12], CNPq, 24.IX.2020. IG12 (-3,542070; -52,725990), (1♂), [n°13], 24.IX.2020. IG12 (-3,542070; -52,725990), (1♂), [n°14], 24.IX.2020. IG12 (-3,542070; -52,725990), (1♂), [n°15], 24.IX.2020. IG12 (-3,542070; -52,725990), (1♀), [n°16], 30.X.2021. IG11 (-3,407750; -52,735600), (1♂), [n°17], 28.IX.2020. IG22 (-3,154167; -52,154333), (1♂), [n°18], 30.X.2021. IG14 (-3,141980; -52,269090), (2♂), [n°28], 17.IX.2020. IG14 (-3,141980; -52,269090), (3♂), [n°30], 17.IX.2020. IG12 (-3,542070; -52,725990), (1♂), [n°31], 24.IX.2020. IG14 (-3,141980; -52,269090), (1♂), [n°32], 17.IX.2020. IG14 (-3,141980; -52,269090), (3♂), [n°33], 21.IX.2020. IG14 (-3,141980; -52,269090), (1♀), [n°39], 17.IX.2020. IG12 (-3,542070; -52,725990), (1♂), [n°51], 24.IX.2020. IG11 (-3,407750; -52,735600), (1♂), [n°52], 28.IX.2020. IG08 (-3,439970; -52,331670), (1♂), [n°54], 06.X.2020. IG10 (-3,267409; -52,250587), (1♀,2♂), [n°56], 08.X.2020. IG10 (-3,267409; -52,250587), (1♀), [n°57], 08.X.2020. IG05 (-3,328250; -52,407440), (1♀), [n°59], 01.X.2020. IG04 (-3,297310; -52,413950), (1♀), [n°60b], 25.IX.2029. IG11 (-3,407750; -52,735600), (1♀), [n°61], 28.IX.2020. IG11 (-3,407750; -52,735600), (1♂), [n°61a], 28.IX.2020. IG31 (-3,282000; -52,329997), (1♂), [n°328], 18.XI.2023. IG30 (-3,322997; -52,265997), (1♂), [n°396], 17.XI.2023. IG21 (-3,320510; -52,331320), (1♀), [n°397], 19.X.2023. IG25 (-3,253600; -51,914400), (1♀), [n°398], 11.XI.2023. IG27 (-3,161097; -51,999000), (1♀), [n°399], 13.XI.2023. IG26 (-3,154197; -51,983700), (1♂), [n°631], 11.XI.2023. IG14 (-3,141980; -52,269090), (1♀), [n°657], 17.IX.2020. IG01 (-3,086100; -51,634950), (1♂), [n°64], 11.IX.2019. IG03 (-3,009150; -51,768367), (1♀), [n°639], 24.IX.2019. IG23 (-3,434917; -51,621250), (1♀), [n°641], 13.IX.2019. IG02 (-3,025183; -51,722417), (1♂), [n°658], 24.IX.2019. IG01, (1♂), [n°662], 11.IX.2019.

Ranatra magna Kuitert, 1949

Figure 4 B/Figure 6 (a-e)/Figure 9 (d)/Figure 10 (d).

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Figure 6
Images of Ranatra Fabricius, 1790 species. Ranatra magna (a) dorsal view of female, (b) ventral view of female, (c) dorsal view of male, (d) ventral view of male, (e) interocular space of female; Ranatra mediana (f) dorsal view of female, (g) ventral view of female, (h) dorsal view of male, (i) ventral view of male, (j) interocular space of female; Ranatra mixta (k) dorsal view of female, (l) ventral view of female, (m) dorsal view of male, (n) ventral view of male, (o) interocular space of female.

Distribution in Brazil: AM, PA (Kuitert 1949, Nieser 1975, Cunha et al. 2015, De Lima et al. 2026, This study).

Taxonomic comments: This species is notable for its large body size, with males measuring 48–49 mm and females exceeding 50 mm (De Carlo 1964).

Comments: The only species approaching the body size of R. magna is R. tuberculifrons, but they are clearly distinct due to the tubercle present in the interocular region of R. tuberculifrons.

Examined material: IG04 (-3,297310; -52,413950), (♂), [n°29], 30.IX.2020. IG12 (-3,542070; -52,725990), (1♀), [n°44], 24.IX.2020. IG14 (-3,141980; -52,269090), (1♀), [n°45], 17.IX.2020. IG14 (-3,141980; -52,269090), (1♂), [n°652], 17.IX.2020. IG06 (-3,290360; -52,378140), (1♂), [n°58], 28.IX.2019. IG24 (-3,323150; -52,265870), (1♂), [n°194], 29.IX.2019. IG28 (-3,200500; -51,841200), (1♀), [n°332], 13.XI.2023. IG21 (-3,320510; -52,331320), (1♀), [n°400], 19.X.2023. IG21 (-3,320510; -52,331320), (1♀), [n°401], 19.X.2023. IG25 (-3,253600; -51,914400), (1♀), [n°402], 11.XI.2023. IG23 (-3,434917; -51,621250), (2♀), [n°647], 13.IX.2019. IG01 (-3,086100; -51,634950), (1♀), [n°648], 11.IX.2019. IG05 (-3,328250; -52,407440), (1♂), [n°655], 01.X.2020. IG05 (-3,328250; -52,407440), (2♀), [n°664], 01.X.2020. IG20, (1♀), [n°727], 09.IX.2024.

Ranatra mediana Montandon, 1910

Figure 4 B/Figure 6 (f-j)/Figure 9 (e)/Figure 10 (e).

Distribution in Brazil: PA (Nieser 1975, De Lima et al. 2026, This study).

Taxonomic comments: Body length ranges from 29 to 32 mm, and the respiratory siphon reaches the anterior margin of the pronotum. The individuals have a dark brown coloration with pale legs and faint dark stripes (Nieser 1975).

Comments: The female operculum usually does not extend beyond the tip of the abdomen. Therefore, females do not have dorsal teeth visible past the abdomen.

Examined material: IG22 (-3,154167; -52,154333), (1♂), [n°24], 30.X.2021. IG22 (-3,154167; -52,154333), (1♂), [n°25], 30.X.2021. IG04 (-3,297310; -52,413950), (3♂), [n°60a], 25.IX.2019. IG02 (-3,025183; -51,722417), (1♂), [n°258], 11.IX.2019. IG30 (-3,322997; -52,265997), (1♂), [n°334], 17.IX.2023. IG30 (-3,322997; -52,265997), (1♀), [n°377], 17.XI.2023. IG21 (-3,320510; -52,331320), (1♀), [n°378], 19.X.2023. IG23 (-3,434917; -51,621250), (1♂), [n°634], 13.IX.2019. IG03 (-3,009150; -51,768367), (1♀), [n°635], 24.IX.2019. IG02 (-3,025183; -51,722417), (1♀), [n°650], 24.IX.2019. IG14 (-3,141980; -52,269090), (1♀), [n°651], 17.IX.2020. IG02 (-3,025183; -51,722417), (1♀), [n°653], 24.IX.2020. IG01, (1♂), [n°656], 11.IX.2019. IG18 (-3,367100; -52,876000), (1♀), [n°730], 06.IX.2024.

Ranatra mixta Montandon, 1907

Figure 4 B/Figure 6 (k-o)/Figure 9 (f)/Figure 10 (f).

Distribution in Brazil: PA (Nieser 1975, This study).

Taxonomic comments: This species resembles R. moderata and R. doesburgi, but differs because the female operculum in R. mixta extends more than 1 mm beyond the tip of the abdomen and the respiratory siphon is relatively small (Nieser 1975).

Comments: Females have 10–11 dorsal opercular teeth that are visible beyond the end of the abdomen.

Examined material: IG11 (-3,407750; -52,735600), (1♀), [n°55], 28.IX.2020. IG12 (-3,542070; -52,725990), (1♀), [n°62], 24.IX.2020. IG09 (-3,359360; -52,288170), (2♀), [n°63], 07.X.2020. IG22 (-3,154167; -52,154333), (2♀), [n°192], 30.X.2021. IG22 (-3,154167; -52,154333), (1♀), [n°193], 30.X.2021. IG32 (-3,272400; -52,142497), (1♀), [n°333], 19.XI.2023. IG21 (-3,320510 ; -52,331320), (1♀), [n°379], 19.X.2023. IG30 (-3,322997; -52,265997), (1♂), [n°380], 17.XI.2023. IG21 (-3,320510; -52,331320), (1♀), [n°381], 19.X.2023. IG30 (-3,322997; -52,265997), (1♀), [n°382], 17.XI.2023. IG21 (-3,320510; -52,331320), (2♀), [n°383], 19.X.2023. IG27 (-3,161097; -51,999000), (1♀), [n°384], 13.XI.2023. IG03 (-3,009150; -51,768367), (1♀), [n°637], 24.X.2023. IG23 (-3,434917 ; -51,621250), (4♀), [n°640], 13.IX.2019. IG18 (-3,367100; -52,876000), (1♀), [n°728], 06.IX.2024.

Ranatra moderata Kuitert, 1949

Figure 4 B/Figure 7 (a-e)/Figure 9 (g)/Figure 10 (g).

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Figure 7
Images of Ranatra Fabricius, 1790 species. Ranatra moderata (a) dorsal view of female, (b) ventral view of female, (c) dorsal view of male, (d) ventral view of male, (e) interocular space of female; Ranatra obscura (f) dorsal view of male, (g) ventral view of male, (h) interocular space; Ranatra parvula (i) dorsal view of female, (j) ventral view of female, (k) interocular space of female; Ranatra rabida (l) dorsal view of male, (m) ventral view of male, (n) interocular space of male; Ranatra sp. 1, (o) dorsal view of male, (p) ventral view of male, (q) interocular space of male.

Distribution in Brazil: AM, PA (Kuitert 1949, Nieser 1975, This study).

Taxonomic comments: Individuals have body lengths ranging from 37 to 40 mm, and the females are larger. Respiratory siphons range from 24 to 26 mm (Nieser 1975).

Comments: The subapical tooth on the male paramere is obtuse.

Examined material: IG12 (-3,542070; -52,725990), (1♂), [n°26], 24.IX.2020. IG15 (-3,141980; -52,269090), (1♀), [n°27], 21.IX.2020. IG30 (-3,322997; -52,265997), (1♂), [n°391], 17.XI.2023. IG21 (-3,320510; -52,331320), (1♂), [n°392], 19.X.2023. IG21 (-3,320510; -52,331320), (1♀), [n°393], 19.X.2023. IG29 (-2,918100; -51,956097), (1♀), [n°394], 16.XI.2023. IG25 (-3,253600 ; -51,914400), (1♂), [n°395], 11.XI.2023. IG05 (-3,328250; -52,407440), (1♂), [n°661], 11.X.2020. IG19 (-3,280067; -52,862883), (1♀), [n°729], 08.XI.2024.

Ranatra obscura Montandon, 1907

Figure 4 D/Figure 7 (f-h)/Figure 10 (h).

Distribution in Brazil: PA, AM, RS, SC (De Carlo 1964, Nieser 1975, Cunha et al. 2015, De Lima et al. 2024, 2026, This study).

Taxonomic comments: This species measures between 30 and 34 mm, and its respiratory siphon reaches the pronotum when folded alongside the body, measuring approximately 20–25 mm. The individuals have dark bodies with pale legs and dark stripes (De Carlo 1964, Nieser 1975).

Comments: They may be confused with R. doesburgi, but that species is larger and males lack the subapical tooth on the paramere, whereas males of R. obscura have a low and obtuse subapical tooth (Nieser 1975).

Examined material: IG22 (-3,154167; -52,154333), (1♂), [n°19], 30.X.2021. IG14 (-3,141980; -52,269090), (1♂), [n°20], 17.IX.2020. IG22 (-3,154167; -52,154333), (1♂), [n°22], 30.X.2021. IG17 (-3,320510; -52,331320), (1♂), [n°23], 09.IX.2020. IG10 (-3,267409; -52,250587), (1♂), [n°259], 08.X.2020. IG33 (-3,387997; -52,143997), (1♂), [n°325], 19.XI.2023. IG33 (-3,387997; -52,143997), (1♂), [n°329], 19.XI.2023. IG05 (-3,328250; -52,407440), (1♂), [n°638], 26.IX.2019. IG14 (-3,141980; -52,269090), (1♂), [n°643], 17.IX.2020. IG14 (-3,141980; -52,269090), (1♂), [n°649], 17.IX.2020.

Ranatra parvula Kuitert, 1949

Figure 4 C/Figure 7 (i-k)/Figure 9 (h).

Distribution in Brazil: AM, PA (Kuitert 1949, De Carlo 1964, Nieser 1975, This study).

Taxonomic comments: These are smaller individuals measuring between 24 and 30 mm (♂ 24–25 mm, ♀ 30 mm), with respiratory siphons longer than the body. The female operculum does not extend beyond the tip of the abdomen (Nieser 1975).

Comments: They exhibit a brown coloration with legs nearly the same color, sometimes slightly paler, and with faint transverse stripes on the body in light brown.

Examined material: IG12 (-3,542070; -52,725990), (1♀), [n°43], 24.IX.2020. IG30 (-3,322997; -52,265997), (1♀), [n°330], 17.XI.2023. IG30 (-3,322997; -52,265997), (2♀), [n°376], 17.XI.2023.

Ranatra rabida White, 1879

Figure 4 C/Figure 7 (l-n)/Figure 10 (i).

Distribution in Brazil: AM, PA! (White 1879, Nieser 1975, This study).

Taxonomic comments: Individuals have body lengths of 28–30 mm, with females being slightly larger. Their coloration is dark brown with paler legs and faint stripes (De Carlo 1946, 1964, Nieser 1975).

Comments: This species represents an expansion of its known distribution into the state of Pará. It resembles R. adelomorpha and R. parvula, but differs in body structure, since R. rabida is more robust (Nieser 1975).

Examined material: IG30 (-3,322997; -52,265997), (1♂), [n°629], 17.XI.2023. IG30 (-3,322997; -52,265997), (1♂), [n°630], 17.XI.2023.

Ranatra tuberculifrons Montandon, 1907

Figure 4 C/Figure 8 (a-f)/Figure 9 (i)/Figure 10 (j).

thumbnail of Figure 8
Figure 8
Images of Ranatra Fabricius, 1790 species. Ranatra tuberculifrons (a) dorsal view of female, (b) ventral view of female, (c) dorsal view of male, (d) ventral view of male, (e) interocular space of female, (f) tubercle view of female.

Distribution in Brazil: AM, PA (Nieser 1975, Cunha et al. 2015, This study).

Taxonomic comments: Individuals of this species have a tubercle in the interocular region, and their body size ranges from 39 to 45 mm (Nieser 1975).

Comments: The respiratory siphon reaches about halfway along the body or slightly shorter, and the female operculum extends approximately 1 mm beyond the tip of the abdomen.

Examined material: IG16 (-3,108850; -52,225470), (1♀), [n°34], 23.IX.2020. IG07 (-3,323150; -52,265870), (1♀), [n°35], 04.X.2020. IG13 (-3,470820; -52,744640), (1♂), [n°36], 29.IX.2020. IG11 (-3,407750; -52,735600), (1♀), [n°37], 28.IX.2020. IG14 (-3,141980; -52,269090), (1♂), [n°38], 21.IX.2020. IG12 (-3,542070; -52,725990), (1♂), [n°62a], 24.IX.2020. IG33 (-3,387997; -52,143997), (1♂), [n°326], 19.XI.2023. IG25 (-3,253600; -51,914400), (2♂), [n°375], 11.XI.2023. IG23 (-3,434917; -51,621250), (1♀), [n°642], 13.IX.2019. IG23 (-3,434917; -51,621250), (1♂), [n°645], 13.IX.2019. IG03 (-3,009150; -51,768367), (1♀), [n°646], 24.IX.2019.

Ranatra sp. 1

Figure 4 C/Figure 7 (o-q)/Figure 10(k).

Distribution in Brazil: PA (This study).

Taxonomic comments: Males measure approximately 38 mm, with respiratory siphons reaching up to 36 mm, while females are larger, with body lengths between 38 and 39 mm. The male paramere lacks a subapical tooth and is distinctly truncated at the top of the paramere (De Carlo 1970). The individuals analyzed have eyes of average size, being larger than the interocular space.

Comments:Ranatra sp. 1 shows morphological characteristics that clearly separate it from other species of the genus recorded for the region. The species R. sp. 1 is very similar to the description of the species R. usingeri described by De Carlo (1970), possessing many similar characteristics. Although R. usingeri was synonymized with R. doesburgi by Nieser (1975), it is possible to observe differences between these two species. According to De Carlo (1970), R. usingeri differs from R. doesburgi mainly in body size, as R. doesburgi is smaller and presents light-colored legs with darker bands, a feature not reported for R. usingeri.

Examined material: IG31 (-3,282000; -52,329997), (1♂), [n°626], 18.XI.2023. IG31 (-3,282000; -52,329997), (1♂), [n°627], 18.XI.2023. IG31 (-3,282000; -52,329997), (2♂), [n°628], 18.XI.2023.

DISCUSSION

Of the 35 Ranatra species recorded for Brazil, 13 were registered in this study for the tributaries of the Xingu River, in addition to three distribution expansions for the state of Pará, R. brasiliensis, R. doesburgi, and R. rabida. Other studies conducted in the region reported lower species richness, recording at most four species, which highlights the relevance of this study (Cunha et al. 2015, Cunha & Juen 2017) and reinforces the singular diversity of the genus in this region.

The last study on aquatic Heteroptera for the northern region of Brazil was conducted in 2011 (Moreira et al. 2011), demonstrating how scarce research on Ranatra species remains. Studies on benthic invertebrates are also limited in northern Brazil, with a research rate of less than 7% compared to other regions (Carvalho et al. 2023). For the genus Ranatra, the literature on species distribution and descriptions is outdated and lacks clear illustrations, as seen in the works of De Carlo (1964, 1970, 1972) and Nieser (1975). This hampers the process of species-level identification, resulting in a superficial dataset for the group in the region.

The development of an updated species list for the tributaries of the Xingu River on endemism areas represents a major advance in documenting Amazonian aquatic biodiversity. Ongoing environmental degradation in the region, located within the deforestation arc, makes it increasingly likely that these and other species may disappear before they are even known to science (Almeida et al. 2014). Therefore, studies such as this one effectively help reduce the Linnean and Wallacean shortfalls, contributing critically to the knowledge, monitoring, and conservation of aquatic biodiversity in one of the most threatened regions of the country.

CONCLUSIONS

Studies on aquatic species in the Tapajós and Xingu area of endemism are still in their early stages, especially for aquatic groups that are not evaluated by the International Union for Conservation of Nature (IUCN) or by the Chico Mendes Institute for Biodiversity Conservation (ICMBIO). In this study, we documented three distribution expansions for the state of Pará, contributing to the understanding of these organisms in the tributaries of the Xingu River, within the Tapajós and Xingu areas of endemism. However, little is known about the basic biology and distribution of species of the genus Ranatra in Brazil.

Acknowledgements

This study was funded by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) under grant Nº 28/2018 (process Nº 420827/2018-8), and Nº 10/2023 (process Nº 420569/2023-5), and by Fundação Amazônia de Apoio ao Estudo e à Pesquisa (FAPESPA) through the Interpará III program, ICAAF Nº 001/2018. EVD thanks PIBIC/UFPA for the research fellowship and CNPq/PROTAX process 445854/2024-3, for the master’s degree scholarship (scholarship application process: 131300/2026-1) and programa de Pós-Graduação em Ecologia – PPGECO. ESL acknowledges CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for the doctoral scholarship (process 88887.841990/2023-00), and Embaixada da França no Brasil, no âmbito do Centro Franco-Brasileiro da Biodiversidade Amazônica, pela bolsa de mobilidade do Governo Francês (Campus France/Dossier nº 184202R). ISC acknowledges CNPq for the doctoral scholarship (process 141501/2024-3). We also thank CNPq for the research productivity grants awarded to KDS (process 311550/2023-1) and LJ (process 304710/2019-9). We are grateful for the support provided by the following projects: PPBIO AmOr (Programa de Pesquisa em Biodiversidade da Amazônia Oriental – CNPq/MCTI/FNDCT Nº 07/2023, process 441257/2023–2), PELD-AmOr (Monitoramento de Padrões Socioecológicos de Longo Prazo nos Ecossistemas da Amazônia Oriental – CNPq process 445970/2024-3), and INCT SinBiAm (Instituto Nacional de Ciência e Tecnologia para a Síntese da Biodiversidade Amazônica – CNPq/MCTIC/INCT-2022, editais 58/2022, process 406767/2022–0).

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Edited by

  • Handling editor
    Marcela Lima

Data availability

The data collected and generated during this study are available on Google Drive at: https://docs.google.com/spreadsheets/d/1OP0bCxc_vc78tv3bz_l1eeLtR4ViABnz/edit?usp=sharing&ouid=112085920248005140401&rtpof=true&sd=true. The authors confirm that all data necessary to reproduce the results of this study are available in the designated dataset.

Publication Dates

  • Publication in this collection
    28 Aug 2026
  • Date of issue
    2026

History

  • Received
    10 Dec 2025
  • Accepted
    06 Apr 2026
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