Stenaelurillus fuscatus

Stenaelurillus fuscatus was first described by Wanda Wesołowska & Anthony Russell-Smith in 2000.[1] The species name is the Latin word that means darkish.[2] It was placed in the genus Stenaelurillus, first raised by Eugène Simon in 1886.[3] The genus name relates to the genus name Aelurillus, which itself derives from the Greek word for cat, with the addition of a Greek stem meaning narrow.[4] It was placed in the subtribe Aelurillina in the tribe Aelurillini by Wayne Maddison in 2015, who listed the tribe in the clade Saltafresia.[5] Two years later, in 2017, it was grouped with nine other genera of jumping spiders under the name Aelurillines.[6]

The spider is medium-sized. The male has a carapace that is 2.6 mm (0.10 in) long and 2 mm (0.079 in) wide and abdomen that is 2.8 mm (0.11 in) long and 2.0 mm (0.079 in) wide.[7] The carapace is dark brown and has two faded white stripes on the thorax. The abdomen is very hairy, with dense long black hairs dominating, although there is a small corridor of white hairs on the dark brown scutum that covers the majority of the surface. Underneath, the abdomen is yellowish, but this is hard to see. The eye field is small, black and bristly. The chelicerae and clypeus are light brown, and there three small teeth visible. The spider has long hairy yellow spinnerets. The legs and pedipalps are brownish, the pedipalps also having long black hairs. The palpal bulb has a very large bulb at the rear while the embolus has a distinctive hook near the base. Other than the sexual organs, the male is similar to Stenaelurillus darwini and Stenaelurillus uniguttatus.[2]

The female is similar to the male in shape but slightly larger. The carapace is between 2.5 and 3.2 mm (0.098 and 0.126 in) long and between 1.95 and 2.35 mm (0.077 and 0.093 in) wide while the abdomen has a length between 3 and 3.6 in (76 and 91 mm) and width of 2.6 and 2.95 mm (0.102 and 0.116 in).[8] The carapace is similar in colour to the male but the white stripes are more pronounced and extend onto the abdomen. The abdomen also has a more prominent pattern with a white triangular marking and oval spot formed of white scales. There are also numerous speckles visible underneath. The clypeus is yellow-brown but the chelicerae and legs are brown. The spinnerets also have a browner tint. The epigyne is flat with visible structures and a barely visible pocket. The copulatory openings are widely spaced and ovoid.. It has very short and wide insemination ducts and ovoid spermathecae.[9] The female can be distinguished from Stenaelurillus darwini by the wider insemination ducts.[10] Compared to Stenaelurillus latibulbis, the copulatory organs lack sclerotization.[11]

The species is endemic to Tanzania.[1] The holotype was found near the Umba River in the Mkomazi National Park in 1995.[12] It was also subsequently found in the forests of Matthews Range and the coastal regions of Kenya. It thrives in exposed environments, like rocks.[10]