Rimanella

Rimanella arcana is a species of damselfly endemic to the Guiana Highlands of northern South America. It is the sole species in the genus Rimanella, which in turn is the only genus in the family Rimanellidae.^[5]

Known as the Pantepui relict damsel, the species inhabits streams and waterfalls in the tepui region of Venezuela, Guyana, Suriname and northern Brazil.^[1] It is a distinctive damselfly with narrow transparent wings, a slender dark body and unusual wing venation.^[2]

The species was originally described by Needham in 1933 as Rima arcana. The following year he replaced the genus name with Rimanella because the original name was already in use for another animal genus.^[2][3]

Rimanella arcana is a medium-sized damselfly with a wingspan of about 30 mm and a slender body approximately 41 mm long.^[2] Adults are predominantly dark greenish-black and brown, with a yellow face, brown thorax and transparent wings bearing a brown pterostigma.^[2]

When describing the genus, Needham noted that its wing venation differed markedly from that of other known damselflies and considered it most closely related to the genera Megalestes and Hypolestes, while differing from both in several important characters.^[2] He regarded the insect as sufficiently distinctive to warrant placement in a new genus.^[2]

Needham described the species in 1933 as Rima arcana from material collected on Mount Duida in Venezuela.^[2] The following year he replaced the genus name with Rimanella after discovering that Rima was preoccupied.^[3]

For much of the twentieth century, Rimanella was included in Amphipterygidae together with several geographically isolated genera from Central America, Africa and Asia.^[6] Fraser (1957) later transferred the genus to Pseudolestidae, a family created to accommodate a number of morphologically unusual damselfly genera whose relationships were uncertain.^[7]

Novelo-Gutiérrez (1995) observed similarities between the larvae of Rimanella and the African genus Pentaphlebia, particularly the distinctive gill tufts, and placed the two genera together in the subfamily Pentaphlebiinae.^[8] Subsequent morphological and molecular studies showed that the traditional concept of Amphipterygidae did not represent a natural group.^[9][10][11]

Modern classifications recognise Rimanellidae as a separate monogeneric family containing only Rimanella arcana.^[11][5]

Needham originally named the genus Rima in 1933. He explained that the name was taken from Rima, the heroine of William Henry Hudson's Venezuelan novel Green Mansions.^[2] Because the generic name was already occupied, Needham introduced the replacement name Rimanella in 1934, retaining the original stem of the name.^[3]

The species name arcana is derived from the Latin arcanus ("hidden", "secret" or "mysterious"), possibly referring to the remote and little-known region in which the species was discovered.^[2]