They can be distinguished from the closely-related Evarcha praeclara by the patterns on their body, including a semi-lunar marking in the middle of its carapace and a light stripe on its abdomen.

The female has a characteristic depression in the middle of its epigyne and narrow insemination ducts that lead to complex spermathecae.

Evarcha seyun is a species of jumping spider that was first described by Wanda Wesołowska and Antonius van Harten in 2007.

[2] It was one of over 500 species identified by the Polish arachnologist Wesołowska during her career, more than any other contemporary writer and second only to Simon in the history of the science.

[4] In 1976, Jerzy Prószyński placed the genus Evarcha in the subfamily Pelleninae, along with the genera Bianor and Pellenes.

[5] In Wayne Maddison's 2015 study of spider phylogenetic classification, the genus Evarcha was moved to the subtribe Plexippina.

[11] This designation is not widely accepted and the species remains in the Evarcha genus in the World Spider Catalog.

[13] Evarcha seyun is a small spider with a body divided into two main parts: cephalothorax and an abdomen.

The rounded carapace, the hard upper part of the cephalothorax, is dark brown with a darker rear and a lighter semi-lunar marking in the middle.

Its legs are black, orange and yellow and marked with a large number of long brown spines.

[17] Its abdomen has a yellowish top with white spots forming a pattern divided into three segments by darker lines.

[17][20] The spider is closely related to Evarcha praeclara, but can be clearly identified by the difference in their external patterns.

The male has a shorter tibial apophysis, which resembles that on Evarcha armeniaca, although the clear difference in the shape of the embolus on this spider means that they can still be differentiated.

[21] Evarcha seyun is endemic to the Arabian Peninsula and lives in the United Arab Emirates and Yemen.