# Pachyballus mombasensis

Pachyballus mombasensis is a species of jumping spider in the genus Pachyballus that is endemic to Kenya. The species was first described in 2020 by Wanda Wesołowska, Galina Azarkina and Konrad Wiśniewski. It is a very small brown spider, with a body that consists of a cephalothorax that is between 1.1 and 1.3 mm (0.04 and 0.05 in) long and an abdomen that is typically 2.1 mm (0.08 in) long. The spider is dark brown, apart from its darker eye field and yellow legs, although the front pair of male's legs are also brown. Otherwise, the male and female look very similar to the related ' Pachyballus castaneus and Pachyballus flavipes. It is necessary to look at the spiders' copulatory organs to distinguish them from others in the genus, particularly the shorter length of the female's insemination ducts and the size of the palpal bulb.

## Taxonomy and etymology

Pachyballus mombasensis is a species of jumping spider that was first described by the arachnologists Wanda Wesołowska, Galina Azarkina and Konrad Wiśniewski in 2020. It is one of over 500 different species identified by Wesołowska in her career. It has a species name relates to the place where the spider was first found. They allocated the spider to the genus Pachyballus, first circumscribed in 1900 by Eugène Simon.
When he first established the genus, Simon assigned Pachyballus to the Balleae group alongside the related genus Peplometus. In their 2003 phylogenetic analysis, Wayne Maddison and Marshall Hedin noted that the genus is closely related to Mantisatta, despite the large physiological differences between them, and the similarity of those spiders with a group of genera they termed Marpissoida. In 2004, Suresh Benjamin tentatively included in the genus, along with Ballus, in his subfamily Ballinae. In 2007, Wesołowska and Anthony van Harten noted the similarity of the genus with Planiemen. In 2015, Maddison listed the genus within the tribe Ballini, derived from Simon's original name, but attributed to an earlier author, Nathan Banks from 1892. He allocated the tribe to the clade Marpissoida in the clade Salticoida. In 2016, Jerzy Prószyński added the genus to a group of genera termed Ballines, which contains many of the same genera, including Ballus, Peplometus and Planiemen. It is likely that the ballines diverged from the wider Marpissoida clade between 20 and 25 million years ago, although Daniela Andriamalala estimated the family to be 3.99 million years old.

## Description

Pachyballus mombasensis is a wide-bodied spider that, like other members of the genus, resembles a beetle the family Chrysomelidae. This may be a form of camouflage, enabling it to hide amongst trees. It is also very similar externally to the related related Pachyballus castaneus and Pachyballus flavipes. It is small and very flat with a strongly pitted exterior that shows signs of sclerotization. The spider's body is divided into two main parts: a round cephalothorax and a heart-shaped abdomen. The male has a cephalothorax that is typically 1.1 mm (0.04 in) long, and 1.1 mm (0.04 in) wide The carapace, the hard upper part of the cephalothorax, is dark brown. The eye field is darker, nearly black, with a few colourless bristles near the front row of eyes. The chelicerae have three teeth to the back, while the remainder of the mouthparts, including are brown, except for small white edging to the labium and maxillae.
The spider's abdomen is flat and is typically 2.1 mm (0.08 in) in length and width. Its topside is dark brown while its underside is dominated by a scutum, which is similar to other species in the genus. The first pair of legs are brown with two spines and dense furry hairs. The remainder of the legs are mainly yellow with brown parts. It has distinctive copulatory organs. The male has rounded cymbium that has a bulge at the top while the palpal bulb has a pronounced bulge to the bottom. The very thin wiry embolus sprouts from the top the bulb in a coil and then projects upwards. The palpal tibia is small and has an erect protrusion, or tibial apophysis, that has a slight bulge on it. This is very similar to Pachyballus flavipes, differing only in that the apophysis on this species hugs close to the cymbium. Its palpal bulb is wider than Pachyballus castaneus and its embolus has a looser coil.
The female is larger than the male, with a carapace that is typically 1.5 mm (0.06 in) long. In general it is similar to the male, although the front legs are the same as the others and it has a large scutum on its back. Both its top and bottom are mainly dark brown. Like the male, the female's copulatory organs are distinctive. The epigyne, the external part of the copulatory organs, has a semi-circular depression to the back and two copulatory openings near the front that lead, via relatively short insemination ducts that loop around once, to relatively large spermathecae, or receptacles. The spermathecae show evidence of sclerotization. The shorter length of the insemination ducts distinguish the species from Pachyballus flavipes and Pachyballus miniscutulus.

## Distribution

Pachyballus spiders generally live in Africa and have been found in Yemen.Pachyballus mombasensis is endemic to Kenya. The male holotype was discovered in 1970 on Diani Beach, 30 km (19 mi) south of Mombasa. Other examples have been found locally.