Trichogenes claviger

Trichogenes claviger, the Caetés catfish, is a critically endangered species of pencil catfish native to the Atlantic Forest of Brazil. It was discovered early in 2010 and scientifically described later in the same year. One of three species within the genus Trichogenes, it is restricted to an area of 16 km² in the Caetés forest, a mountainous area in the Brazilian state of Espírito Santo. When discovered, the rainforest in which it occurs was unprotected and threatened by deforestation, but a private nature reserve has since been established. A small fish, it is up to 50.8 mm in length. A series of black dots run along the side of the body. Males have a bony protrusion from the gill area (the opercular process) that is elongated and club-like, a feature that inspired the name of the species (claviger – 'club-bearing'). The opercular process in T. claviger is the only known secondary sex characteristic in pencil catfishes, and might have evolved for sexual signaling; it is also used by the fish to climb up net walls when caught. The species lives in small, shaded, and slow-moving streams in rainforest and dwells in the middle of the water column, mostly feeding on insects that have fallen on the water surface. It is the only fish in its habitat.