The spider resembles the related Mogrus fulvovittatus, particularly the female, which can only be clearly differentiated by looking the internal structure of its epigyne.

It has a distinctive loop on the end of its embolus and a bulbous base to its single tibial apophysis, or spike.

Mogrus portentosus is a jumping spider that was first described by Wanda Wesołowska and Antonius van Harten in 1994.

[2] In Wayne Maddison's 2015 study of spider phylogenetic classification, the genus Mogrus was placed in the clade Simonida within the subfamily Saltafresia.

[8] The palpal bulb has a single straight tibial apophysis, or spike, that has a bump at its base.

[10] The spider can be easily distinguished from others in the genus by the shape of the male embolus, especially the characteristic loop at the tip, and the way that the base of the spike on the tibia is bulbous.

[7] This led to the authors deciding that one of the examples they thought was a member of this species was actually Mogrus praecinctus.

The spider is known to live in areas of human habitation and some examples have been found in cotton fields.