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In this study we provide an updated list of Plecoptera based on recent collections covering areas from northern to southeastern Tocantins state, Brazil. It is the first work focused on the geographical distribution of the order in this region. Herein, we register Anacroneuria atrifrons Klaplek, 1922, Anacroneuria jaciara Bispo & Neves, 2005, Anacroneuria manauensis Ribeiro-Ferreira, 2001,and Anacroneuria terere Righi-Cavallaro & Lecci, 2010 for the first time to Tocantins with notes and illustrations of diagnostic features for these four species. Our work raises the number of stoneflies known from Tocantins to 13 species.Despite this increase in the number of species, we highlight the importance of expanding field collection efforts in different locations of the state, especially in the west and south regions, as well as increasing collection effort in each location, aiming for a better comprehension of this fauna.

The genus Rineloricaria comprises 69 valid species and has been considered monophyletic by some authors. The taxonomic history of Rineloricaria is quite complex, especially concerning its wide distribution and morphological plasticity that make it difficult to diagnose and describe new species. Even with the great species-richness of the genus and the huge diversity of the system, the Tocantins-Araguaia River basin hosts only three formally described species of Rineloricaria: R. hasemani, R. lanceolata, and R. osvaldoi, the former is known from lower Tocantins River, R. lanceolata widespread along Amazon basin and the last one restricts to the Araguaia River basin. Recent field expeditions and collection examination revealed an undescribed species of the genus from the upper and middle Tocantins River drainage. The new species is diagnosed among its congeners by having a greater number of premaxillary and dentary teeth (both with up to 15 vs. up to 10 in most congeners). From R. hasemani it is also distinguished by having the edge of snout straight in lateral view and absence of filaments on lower lip. It is also diagnosed from R. lanceolata by having wider cleithral width and a quite different color pattern, lacking a hyalin spot on the base of pectoral and pelvic fins; and from R. osvaldoi by having a lower head depth, triangular head in dorsal view, shorter snout length and other features.

An annotated checklist with complementary information for leptophlebiid mayflies from Tocantins State, Brazil is provided. Additionally, we describe a new species of Thraulodes Ulmer, 1920 based on male adults. New reports are based on collections conducted between August 2017 and August 2019 in 13 localities of 10 municipalities. A total of 436 adults distributed in 11 genera, 16 species and five morphospecies treated as undescribed species were collected. Of the total species examined, 11 are new records.

The genus Centromochlus includes eight catfish species in the Amazon and Orinoco river systems: C. schultzi from Xingu and Tocantins-Araguaia rivers; C. melanoleucus from Tapajós and Teles Pires rivers; C. macracanthus from Negro River; C. orca from Nhamundá River; C. heckelii and C. existimatus from Amazon and additionally at the Essequibo rivers; C. carolae and C. musaica from Orinoco River system. Recent field expeditions and collection examination revealed an undescribed species of Centromochlinae that has compatible features with Centromochlus. We herein describe a new species of Centromochlus from the Tocantins-Araguaia River drainage, diagnosed among most Centromochlinae by having a vermiculated color pattern on the dorsum and included in Centromochlus by sharing the derived features: ventrolateral position of eye socket; sphenotic notched for the exit of infraorbital canal; and posterior serrations along pectoral-fin spine numerous. The new species is diagnosed from congeners by having the pectoral-fin spine with dark bars, alternating with light bars (vs. pectoral-fin spine with light and uniform color in all Centromochlus); and it is further distinguished from its congeners (except C. carolae) by the ventral surface of head moderate to largely pigmented (vs. ventral surface of head unpigmented in C. heckelii, C. existimatus, C. orca, C. musaicus, C. schultzi, with few scattered dark chromatophores in C. macracanthus and C. melanoleucus; see diagnosis). A discussion about the systematics of the genus, plus the conservation status of the new species, and an identification key to species of Centromochlus, are also provided.

Megaloptera is a small order of conspicuous holometabolous insects with 397 species and 35 genera distributed worldwide. The order comprises two extant families, the Sialidae (8 genera and 83 species) and the Corydalidae (27 genera and 314 species), both with aquatic larvae, wherea eggs, pupae, and adults are terrestrial (Rivera-Gasperín et al. 2019). Three Corydalidae genera are known from Brazil: Corydalus Latreille, 1802 (11 species), Chloronia Banks, 1908 (4 species) and the monospecific Puri Cardoso-Costa, 2013 (Cardoso-Costa et al. 2013; Rafael Câmara 2020). Whereas, for the Sialidae, only the genus Ilyobius Enderlein, 1910 (3 species) has been found to occur in Brazil (Liu et al. 2015; Rafael Câmara 2020, as ProtosialisVan der Wheele, 1909).

The genus Pseudacanthicus currently comprises the following six species distributed in the Amazon and Tocantins basins, and coastal drainages from Guyana to French Guyana: P. serratus, P. fordii, P. histrix, P. spinosus, P. leopardus, P. pitanga, and P. pirarara. Herein we describe P. major, from rio Tocantins basin, one of the largest loricariid species known. The new species is distinguished from its congeners by the following combination of characters: having body color pattern with dark brown background without spots or blotches and dorsal and caudal fins with transversal white bands; anterior process of compound pterotic with no contacting with the posterior margin of the orbit and by the absence of a conspicuous crest on the posterior edge of parieto-supraocciptal. Other osteological characteristics are further used to diagnose P. major from others congeners. A discussion on gigantism and miniaturization in freshwater fish, ornamental fisheries activities, threats and conservation of the new species are also provided.

This paper provides the first record of order Embioptera for the State of Tocantins, Brazil, with the description of Clothoda tocantinensis sp. nov. This genus has just three previously described species; only C. nobilis (Gerstäcker) has been recorded from Brazil (Amazon basin). An identification key is provided for males of Clothoda.

The Neotropical species of Caenopangonia Kröber are revised herein based on examination of external and internal morphology of type material and specimens from Argentina and Chile. Three currently valid species are recognized: Caenopangonia aspera (Philip, 1958), Caenopangonia brevirostris (Philippi, 1865), and Caenopangonia hirtipalpis (Bigot, 1892). Two new species are described, Caenopangonia cerdai n. sp. Krolow, Henriques & González (Chile, Chacabuco) and Caenopangonia coscaroni n. sp. Krolow, Henriques & González (Chile, Malleco). We provide diagnosis and/or descriptions, distribution records, illustrations and discussion for all species, as well a key for identification.

The genus Spiroberotha Adams, 1989 is classified in Berothidae (Neuroptera) with two described species: S. fernandezi Adams, 1989 from Venezuela and S. sanctarosae Adams, 1989 from Colombia, Costa Rica and Venezuela. Here we describe a new species, S. tocantinensis n. sp., from Palmas, Tocantins, Brazil. This is the first record of the genus in Brazil, extending its geographical distribution.

The genus Acanthicus is diagnosed from remaining Loricariidae genera by several characters, including the absence of adipose fin, pectoral-fin spine enlarged and the presence of small plates in abdomen region. Acanthicus currently comprises two valid species: A. hystrix and A. adonis. Acanthicus hystrix is distinguished from A. adonis, mostly by having body and fins dark brown to almost completely black background colored, without clear spots or dots (vs. dark brown color background with white spots covering body and fins) and presence of ochre to grey stripes in caudal fin (vs. stripes absent on caudal fin). The holotype of A. hystrix was destroyed during a bombing raid in the Second World War, no neotype was designed and the species is recognized by the illustration present in the original description, whose text is short, and uninformative. In the present contribution, specimens from several institutions were examined, revealing that the species is widespread in the Amazon, Tocantins-Araguaia and Orinoco basins, while A. adonis is restricted to the lower rio Tocantins. Herein, a redescription of Acanthicus hystrix is provided, with a comprehensive diagnosis of the genus and its species, along with a distribution map of the genus, a key to species identification, and brief comments on the systematics and distribution of the genus.

The genus Pseudacanthicus comprises five valid species distributed in the Amazon, Guyana and Suriname basins: P. serratus, P. fordii, P. histrix, P. spinosus and P. leopardus. A new species of Pseudacanthicus from the Tocantins river basin is described. The new species is distinguished from its congeners by the following combination of characters: presence of dark blotches anostomosing to form continuous zigzag bands alongside longitudinal keels; absence of blotches on ventral surface of body; faint blotches on head; all fins with orange to red color on unbranched ray and sometimes on subsequent branched rays; and sphenotic and sixth infraorbital not in contact. Brief comments on the phylogeny of the genus, ornamental fisheries activities, threats and conservation of the new species are also provided.

Two new species of parasitoids, Eibesfeldtphora trifurcata and Eibesfeldtphora inornata, are described. Both species were collected in Brazil. A new key is provided and illustrated for the twenty one known species.