Editorial Type:
Article Category: Research Article
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Online Publication Date: 29 Jun 2022

A New Species of Chaetostoma (Siluriformes: Loricariidae) Expands the Distribution of Rubbernose Plecos Eastward into the Lower Amazon Basin of Brazil

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Page Range: 364 – 377
DOI: 10.1643/i2021068
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A new species of the rubbernose pleco genus Chaetostoma is described from the Maicuru and Seiko Rivers, a northern tributary of the lower Amazon River and a tributary of the lower Xingu River, respectively, both in Pará State, Brazil. The new species is diagnosed from all congeners, except members of the Chaetostoma anale species group, by having an enlarged second unbranched anal-fin ray with posterior paired dermal flaps. Additionally, the new species is distinguished from its only other currently recognized congeners from rivers draining the Guiana Shield (C. jegui and C. vasquezi) by having a smaller opercle and a supraoccipital excrescence undeveloped, comprising a simple skin area present in juveniles and absent in adults. A revised multi-locus phylogeny for the species of Chaetostoma is presented, and the Chaetostoma anale species group is discussed and rearranged.

Uma nova espécie de Chaetostoma é descrita dos rios Maicuru, um afluente norte do baixo rio Amazonas, e Seiko, um afluente do baixo rio Xingu, ambos no estado do Pará, Brasil. A nova espécie é diagnosticada de todos os seus congêneres, exceto membros do grupo Chaetostoma anale, por apresentar o segundo raio não ramificado da nadadeira anal aumentado e com abas dérmicas posteriores. Além disso, a nova espécie se distingue dos únicos outros congêneres atualmente reconhecidos do Escudo das Guianas (C. jegui e C. vasquezi) por ter o opérculo menor e a protuberância supraoccipital não desenvolvida, composta por uma área de pele simples em juvenis e ausente em adultos. Uma filogenia multilocus revisada para as espécies de Chaetostoma é apresentada e o grupo Chaetostoma anale é discutido e reorganizado.

Copyright: © 2022 by the American Society of Ichthyologists and Herpetologists
Fig. 1.
Fig. 1.

Chaetostoma orientale, holotype, MCP 54585, male, 132.4 mm SL. Brazil, Pará, Monte Alegre, Maicuru River.

Fig. 2.
Fig. 2.

Photomicrograph of the modified anal fin of mature male of Chaetostoma orientale, holotype, MCP 54585, male, 132.4 mm SL. (A) Anal fin in ventral view, scale bar = 5 mm; (B) odontodes of anal fin in detail, scale bar = 0.5 mm.

Fig. 3.
Fig. 3.

Photomicrograph of type 3 cheek odontodes of mature male of Chaetostoma orientale, holotype, MCP 54585, 132.4 mm SL. (A) Dorsal view; and (B) lateral view. Scale bar = 2 mm.

Fig. 4.
Fig. 4.

Lips and buccal papillae of Chaetostoma orientale, holotype, MCP 54585, male, 132.4 mm SL. Ventral view. Scale bar 10 mm.

Fig. 5.
Fig. 5.

Live coloration of Chaetostoma orientale at type locality shortly after capture. (A) Paratype, MCP 50363; (B) holotype, MCP 54585.

Fig. 6.
Fig. 6.

Live coloration of Chaetostoma orientale from the Seiko River, shortly after capture. ANSP 199686, photo by Mark Sabaj.

Fig. 7.
Fig. 7.

Geographic distribution of species of Chaetostoma from the Guiana and Brazilian Shields. Star = C. orientale, from Brazil, Pará, Monte Alegre, Maicuru River and Medicilândia, Xingu River, Amazon basin; Dot = C. jegui, from Branco, Uraricoera and Takutu Rivers, Amazon basin; Square = C. vasquezi, from Caura and Caroni Rivers, Orinoco basin. White symbols represent type locality; symbols can represent more than one lot and locality.

Fig. 8.
Fig. 8.

Seiko River, tributary to Jarauçu River, itself a tributary to Xingu River, ca. 3.3 km west of Medicilândia on Trans-Amazon road, 3°27′22.53″S, 52°55′33.61″W. Photo by Mark Sabaj.

Fig. 9.
Fig. 9.

Phylogenetic relationships within the genus Chaetostoma based on ML analysis of a 5,844 base alignment of four mitochondrial (16S, coI, cytb, nd2) and three nuclear (myh6, rag1, rag2) gene regions. Bootstrap support values presented for each node. Chaetostoma anale species group indicated by a black circle. Respective nodes for all species except current and former members of the C. anale species group collapsed to single terminals. Complete results from ML analyses of the concatenated alignment (Fig. S1), alignment of mitochondrial genes only (Fig. S2), and alignment of nuclear genes only (Fig. S3) are available as supplemental files (see Data Accessibility). See Table 1 for additional data on each sample in the analysis. See Data Accessibility for tree file.

Contributor Notes

1 Laboratório de Sistemática de Vertebrados, Pontifícia Universidade Católica do Rio Grande do Sul, Av. Ipiranga, 6681, 90619-900 Porto Alegre, RS, Brazil; Email: (RER) reis@pucrs.br. Send reprint requests to RER.
2 Departamento de Ictiologia, Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Avenida Arenales 1256, Lima 14, Peru.
3 Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013-7012; Present address: Aquatic Ecology and Evolution, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland.
4 Department of Natural History, Royal Ontario Museum, 100 Queens Park, Toronto, ON M5S 2C6, Canada.
5 Laboratório de Ictiologia, Museu de Zoologia da Universidade de São Paulo, Avenida Nazaré, 481, 42694-970 São Paulo, SP, Brazil.
6 School of Biological and Behavioural Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
7 Laboratório de Ictiologia de Altamira, Universidade Federal do Pará, 68372-040 Altamira, PA, Brazil.
8 Coleção de Peixes, Instituto Nacional de Pesquisas da Amazônia, Av. André Araújo, 2936, 69060-001 Manaus, AM, Brazil.

Associate Editor: W. L. Smith.

Received: 31 May 2021
Accepted: 22 Nov 2021
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