Evarcha seyun

Evarcha seyun is a small spider with a body divided into two main parts: cephalothorax and an abdomen. The male has a cephalothorax, that is between 2.2 and 2.3 mm (0.09 and 0.09 in) long and 1.6 and 1.7 mm (0.06 and 0.07 in) wide. The rounded carapace, the hard upper part of the cephalothorax, is dark brown with a darker rear and a lighter semi-lunar marking in the middle. The eye field is black with dense white hairs forming a light patch in the middle, in some examples dividing by two thin fawn lines, and fawn scales around some of the eyes themselves. In some examples, there are horns made of tufts of long dark hairs near the middle eyes. The underside of the cephalothorax, or sternum, is brownish.^[15] The spider's face, or clypeus, is yellowish-brown with a covering of white hairs. Its mouthparts, consisting of the chelicerae, labium and maxillae, are generally brown although there are whitish edges to the tips of the maxillae, which also have a covering of dark hairs.^[6][16]

The male spider's abdomen narrower than the carapace. It measures between 2.0 and 2.3 mm (0.08 and 0.09 in) in length and has a width of between 1.3 and 1.5 mm (0.05 and 0.06 in).^[15] The top is generally dark brown with a white area to the front and a wide white band extending near to the end. The underside is yellow marked with a large dark grey triangular patch. Dense hairs cover the whole abdomen, varying from dark brown to white depending on the background, interspersed with a scattering of longer brown hairs.^[17] The spider has yellow spinnerets, with darker patches visible on the rearmost pair. Its legs are black, orange and yellow and marked with a large number of long brown spines. The pedipalps are brownish-yellow.^[6]

The female has a cephalothorax that is between 2.4 and 2.6 mm (0.09 and 0.10 in) long and 1.7 and 1.9 mm (0.07 and 0.07 in) wide and an abdomen that is between 2.3 and 2.7 mm (0.09 and 0.11 in) long and 1.6 and 1.8 mm (0.06 and 0.07 in) wide.^[15] It is generally hairier that the male.^[6] It It is also slightly larger and lighter. Its carapace is a lighter brown and the eye field dark brown rather than black. It is covered in dense white hairs interspersed with brown bristles. There are tufts of long dark hairs near the eyes like the male. The spider's clypeus has white hairs.^[18] Its abdomen has a yellowish top with white spots forming a pattern divided into three segments by darker lines.^[19]

The spider has distinctive copulatory organs. The male has a rounded palpal bulb with a relatively long embolus that projects from near its top. The embolus is accompanied by a large spatula-like apophysis. There are small hairs on the cymbium and longer hairs on the palpal tibia. The tibia has a short blunt protrusion, or tibial apophysis.^[20] The female has a large rounded depression in the middle of its epigyne. The copulatory openings are mounted to the back and lead to very large many-chambered spermathecae, or receptacles.^[6] The insemination ducts have some sclerotisation, but it is much stronger in the spermathecae. The accessory glands are long.^[18][21]

The spider is closely related to Evarcha praeclara, but can be clearly identified by the difference in their external patterns. For example, this spider's abdomen has a light stripe compared to the lighter patches on the other species.^[3] The female also has a different depression in its epigyne, both in terms of size and shape. The male has a shorter tibial apophysis, which resembles that on Evarcha armeniaca, although the clear difference in the shape of the embolus on this spider means that they can still be differentiated.^[6]

Evarcha spiders live across the world, although those found in North America may be accidental migrants.^[22] Evarcha seyun is endemic to the Arabian Peninsula and lives in the United Arab Emirates and Yemen.^[2] The holotype was discovered in 2002 in Yemen near Seyun, the area after which it is named.^[3] The spider has been observed living in the Al Mahrah and Hadramaut Governorates.^[23]

The first examples identified in the United Arab Emirates were initially found on Jebel Hafeet in 2003. It was subsequently seen at different locations across the Emirates of Ajman and Sharjah. For example, multiple examples were found in Wadi Shawka in 2006 and another female in Wadi Bih in 2008.^[24] In 2010, the species was first found in the Emirate of Umm Al Quwain,^[25] The first example to be identified in the Emirate of Abu Dhabi was first discovered in 2013 living in the Al Wathba Wetland Reserve.^[26] It has been designated as being common across the country.^[27]