Evarcha michailovi

Evarcha michailovi is a species of jumping spider in the genus Evarcha that lives in Europe and Asia. It thrives in dry grassland and heath but has also been found in areas of human habitation, including a railway station. The species was first described in 1992 by Dmitri Logunov. It has a brown to dark carapace that measures between 2.08 and 2.75 mm in length that, in some examples, has light stripes running down its sides. Its black eye field is marked by a white stripe. It has an orange hairy clypeus, or face. It has an abdomen that is between 1.88 and 3.13 mm long, the female being generally larger than the male, but there is a wide variation in the pattern across different specimens. The markings on the carapace helps distinguish the species from others in the genus, as does the species distribution. The copulatory organs are unique, particularly the male embolus and the female epigyne.

Taxonomy and etymology
Evarcha michailovi is a species of jumping spider that was first described by the arachnologist Dmitri Logunov in 1992. He allocated it to the genus Evarcha, first circumscribed by Eugène Simon in 1902. The genus is one of the largest, with members found on four continents. The species is named after the arachnologist Kirill G. Mikhailov.

In 1976, Jerzy Prószyński placed the genus was placed in the subfamily Pelleninae, along with the genera Bianor and Pellenes. In Wayne Maddison's 2015 study of spider phylogenetic classification, the genus Evarcha was moved to the subtribe Plexippina. This is a member of the tribe Plexippini, in the subclade Simonida in the clade Saltafresia. It is closer to the genera Hyllus and Plexippus. Analysis of protein-coding genes showed it was particularly related to Telamonia. In the following year, Prószyński added the genus to a group of genera named Evarchines, named after the genus, along with Hasarinella and Nigorella based on similarities in the spiders' copulatory organs. When he revisited the genus in 2018, Prószyński retained the spider in a truncated Evarcha genus. However, his work is controversial and has not universally accepted.

Description
Evarcha michailovi is a small spider. The spider's body is divided into two main parts, both egg-shaped or ovoid: a more rounded cephalothorax and a more oval abdomen. The male has a carapace, the hard upper part of the cephalothorax, that is between 2.08 and 2.85 mm long and 1.53 and 2.13 mm wide. It is generally dark brown to brown and, in some examples, has two white stripes running down the sides. The eye field is black with a white stripe across its eyes. The underside of the cephalothorax, or sternum, is orange-brown. The spider's face, or clypeus, is orange and covered in thin white and orange hairs. The spider's mouthparts, including orange-brown chelicerae, labium and maxillae.

The male spider's abdomen is between 1.88 and 2.75 mm long and 1.24 and 2 mm wide. Its pattern varies between different examples. Many are dark grey on top, sometimes marked with a pattern of dark line from front to back that has two white oval spots towards the front and black lines across the sides. Some examples have a random pattern of whitish-grey and blackish-brown spots on a greyish-brown surface. Others have a different pattern of dark and light patches.The underside is lighter and uniform brown-grey. The spider has brownish-grey covers to its book lungs and spinnerets. It has mainly brown legs that have yellowish tarsi.The front legs are longer and wider than the others.

The female is slightly larger in size to the male, with a carapace that is between 2.38 and 2.75 mm long, and 1.8 and 2 mm wide and a substantially larger abdomen between 3 and 3.13 mm long, and 1.5 and 1.65 mm wide. It looks similar to the male externally, but is generally lighter. It also differs in details, such as having a greater proportion of its legs yellow. In some examples, the upper surface of the abdomen has a pattern of light and dark patches on a brown background.

The spider's copulatory organs are distinctive. The male has a wide palpal tibia that has a large and blunt protrusion, or tibial apophysis. The palpal bulb is round with a flattened end at the bottom and a fat embolus emanating from at its top. The cymbium is rather large and encloses much of the bulb. There are small hairs on the cymbium and tibia. The female has a pronounced plate at the front of its epigyne that bounds the two copulatory openings. These lead, via short and wide insemination ducts, to unusually shaped spermathecae, or receptacles, with small accessory glands.

Similar spiders
Like most Evarcha spiders, the species is hard to distinguish from others in the genus. However, the species has clear differences in the markings on its carapace. Nonetheless, previously, specimen have been misidentified as the related Evarcha laetabunda, particularly the males. It can be distinguished from this species by its larger size and the presence of a thicker embolus. Other examples have been called Heliophanus simplex, Phlegra fuscipes and Sitticus pubescens.

The female Evarcha michailovi has greater sclerotization on its epigyne and a different spermathecae structure. It can be also be differentiated by the thick walled rim at the back of the epigyne. The spider can also be distinguished by its species distribution. For example, Evarcha michailovi generally prefers drier habitats to other Evarcha species.

Discovery and distribution
Evarcha spiders live across the world, although those found in North America may be accidental migrants. Evarcha michailovi has been found in Central Asia, China, Europe, Kazakhstan, Russia and Turkey. The male holotype was found in 1988 in the Sayano-Shushenski Nature Reserve in Russia amongst the Sayan Mountains. Other examples of the spider were in other areas of the Altai-Sayan region, often at high altitudes. For example, a female was discovered near Todzha Lake in the Azas Nature Reserve at an altitude of 900 m above sea level in 1989. The first example to be found in Kazakhstan the following year amongst the Saur Mountains at an altitude of 1800 m above sea level. It has also been observed in Kyrgyzstan, the first instance being in 1991 alongside the river Arshan in the Terskey Ala-too mountains, and Turkmenistan, on the mountains of the Kopet Dag.

The first time the spider was identified living outside the Soviet Union was in 2001 based on specimens from Tacheng, Xinjang, China, alongside others from Bayantsogt and Bayan-Uul in Mongolia. The Mongolian spiders had been found in 1982 but misidentified. It was subsequently discovered in Turkey, initially in the village of Kavalcık, Reyhanlı, in Hatay Province in 2007.

Meanwhile, the species distribution had been extended into Europe in 2004 by Jean-Claude Ledoux and Michel Emerit. They listed a proliferation of the spiders across France. The first find was a female, a male and four juveniles in Les Eyzies in Dordogne, which had been collected in 1986. Others have been identified in Gard, Hérault and Pyrénées-Orientales The distribution was further extended into the Balkans with a find in 2010 1.1 km north of Sokolarci in Češinovo-Obleševo, North Macedonia, at an altitude of 436 m above sea level. The spider has also been seen living in the Dinaric Alps, which extend into Slovenia at altitudes varying from 359 to 484 m above sea level. It has also been seen in Germany and the Netherlands. Subsequent discovery of the species in Spain proved that its distribution covered the entire continent.

Habitat
The first Evarcha michailovi spiders were found on steppe and along the sides of forests the living amongst Alder and shrubs of genera like Cotoneaster. It has subsequently been found in a wide range of environments. French examples have been seen in dry meadows, heath of Cistus laurifolius and the grass that grows on dykes. The spider also thrives in dry heathland, even when this is undergrowth to coniferous forests. The spider has also been seen in areas of human habitation, including urban areas. Some spiders have been discovered living the railway station at Chulym in 1994. Its conservation status is considered of least concern.

The species lives alongside a number of other spiders, including Agelena labyrinthica, Agyneta affinis, Alopecosa barbipes, Alopecosa schmidti, Asagena phalerata, Drassodes pubescens, Haplodrassus dalmatensis, Micaria dives, Pardosa monticola, Philodromus collinus, Sitticus saltator, Theridion uhligi, Xerolycosa miniata, Xerolycosa nemoralis, Xysticus ninnii, Zelotes electus and Zelotes longipes.