Aelurillus desertus

Aelurillus desertus is a species of jumping spider in the genus Aelurillus that is endemic to the United Arab Emirates. It was first described in 2010 by Wanda Wesołowska and Antonius van Harten. Initially only the male was described, the female following ten years later. The spider was originally classified in the genus Rafalus but was moved to its current genus at the same time as the female description was first published. The species is medium-sized with cephalothorax that is between 2.8 and 3.3 mm long and a abdomen that is between 2.8 and 4.8 mm long. The female is larger than the male. The carapace has a distinctive stripe. The female has three darker spots on the abdomen. The species can be distinguished by the existence of a triangular lobe on the palpal bulb on the male and the way that the copulatory openings are close to the rear of the epigyne on the female.

Taxonomy
Rafalus desertus is a jumping spider that was first described by Wanda Wesołowska and Antonius van Harten in 2010. It is one of over 500 species identified by the Polish arachnologist Wesolowska. The species is named for the desert habitats of the United Arab Emirates.

The spider was placed in the genus Rafalus, named for the Polish arachnologist Jan Rafalski. The genus had been created by Jerzy Prószyński in 1999 based on the discovery of spiders that were related to the genus Aelurillus. The spider was subsequently transferred to Aelurillus in 2020 on the basis of the shape of the embolus and epigyne. Aelurillus was first described by Eugène Simon in 1885. The genus name derives from the Greek word for cat. It was placed in the subtribe Aelurillina in the tribe Aelurillini, both named after the genus, by Wayne Maddison in 2015. These were allocated to the clade Saltafresia. In 2017, the genus was grouped with nine other genera of jumping spiders under the name Aelurillines.

Description
The spider is medium-sized and hairy. The male has a cephalothorax that is between 2.8 and 3 mm in length and 2.2 and 2.3 mm in width. It has a brown striped elongated carapace and a short darker eye field, The abdomen is between 2.8 and 3 mm long and 1.9 and 2 mm wide. It is brown on top with a wide stripe across the middle and yellow underneath. The clypeus is brown with a few white hairs visible. The chelicerae are dark brown with dark hairs and two front teeth. The spinnerets and pedipalps are light while the legs are spotty and between dark yellow and orange in colour. The palpal bulb is mainly covered with light hairs. The tegulum has a complex shape, being large and convex with a distinctive small triangular lobe at it edge. The visible part of the embolus is very small.

The female was first described ten years after the male. It is slightly larger, with a cephalothorax that is 3.1 and 3.3 mm long and 2.5 and 2.6 mm wide and an abdomen 4.2 and 4.8 mm long and 3.4 and 3.7 mm wide. The colouring of the carapace is darker and it is more pear-shaped. The abdomen is similar in colour but has three darker spots and has white hairs and brown bristles. The chelicerae is brown and the legs are light brown. The pedipalps are hairy. The epigyne has weak sclerotization and two pockets towards the back. The spermathecae have multiple chambers and are also sclerotized.

The male can be distinguished from other species by the striped pattern and the triangular lobe on the palpal bulb. The female is best differentiated by looking at the copulatory openings, which are close to the rear of the epigyne unlike most spiders in the genus.

Distribution
Aelurillus desertus is endemic to the United Arab Emirates. It was first found in the Emirate of Ajman, with the holotype collected in 2008. It has also been identified in Al Wathba Wetland Reserve in Abu Dhabi and Al Wasit in Sharjah, with specimens collected in 2010, 2014 and 2015.