The species has a distinctive rounded thorax, after which it is named, and a long thin embolus.

Hyllus rotundithorax is a jumping spider that was first described by Wanda Wesołowska and Anthony Russell-Smith in 2000.

[2] The species name is derived from two Latin words that describe the shape of the spider.

[4] The precise relationship between the genera is unknown but molecular analysis confirms that they are closely related and species from one genus are sometimes misidentified as members of the other.

[7] In Wayne Maddison's 2015 study of spider phylogenetic classification, the genus Hyllus was placed in the clade Saltafresia.

It is also more elongated in shape, covered in light hairs and has a trapezium pattern formed of four hollow dots.

[1] The spider can be differentiated by the rounded shape of the carapace, recalled in the species name, and the structure of the copulatory organs.