# Mecistocephalus evansi

Mecistocephalus evansi is a species of soil centipede in the family Mecistocephalidae. This centipede is notable for featuring 51 pairs of legs rather than the 49 leg pairs usually observed in the genus Mecistocephalus. This species was first described by the French myriapodologist Henry W. Brolemann in 1922. He based the original description of this species on a single female specimen found in the Maysan governorate (formerly Amara province) on the Tigris river in Iraq.

## Distribution and habitats

Since the discovery of the first M. evansi specimen in the Maysan governorate in Iraq, this species has been found in other locations in Iraq, Iran, and Israel. Several specimens have been recorded in Israel, mostly from Mediterranean regions of the Galilee, at higher elevations with lower temperatures and more precipitation. The Israeli specimens include those found in Mount Meron and Gush Halav as well as one found in Be’er Sheva in the Negev desert that may be the result of an anthropogenic transfer. This species has also been found in Gakal Cave in the Kohgiluyeh and Boyer-Ahmad province of Iran, indicating that M. evansi is a troglophile, living in subterranean habitats as well as at the surface. Finally, more Iraqi specimens have been found in the Basrah governorate, including specimens from the Al-Hartha and Shatt Al-Arab districts. Specimens collected from the Basrah governorate include five males and six females found in 2022 on wet agricultural land, in the soil under palm trees, on the left bank of the Shatt Al-Arab river and in the Al-Hartha district.

## Description

This species has 51 pairs of legs and can reach 38 mm in length. The head is shaped like a rectangle and at least twice as long as wide. The dorsal cephalic plate nearly covers the forcipules. The forcipular coxosternite has no chitin-lines and is more than 1.2 times longer than wide. The first article of the forcipule has a distinct intermediate denticle as well as a distal denticle. The ultimate article of the forcipule lacks a distinct basal denticle.
The body is uniform in width for the first four-fifths of its length, then tapers gradually from about the 40th segment to the last segment. The sternites on the anterior part of the trunk, from the second sternite to about the 23rd sternite, feature a distinct median groove that divides into two short branches at the anterior end. A shallow longitudinal impression replaces this groove on the sternites on the posterior part of the trunk. There are no clusters of pores on the ventral surface of the trunk. The posterior end of the last leg-bearing segment has a subtriangular ventral sclerite with a distinctly rounded posterior margin. The ultimate legs have no pretarsus. In adults, the ventral side of the basal element of each ultimate leg has more than twelve scattered pores.
This species shares many traits with other centipedes in the genus Mecistocephalus. For example, like other species in this genus, M. evansi features a head that is evidently longer than wide and a body that tapers towards the posterior end. Furthermore, the coxosternite of the first maxillae is divided. Unlike most other species of Mecistocephalus, however, M. evansi features 51 leg pairs rather than the 49 pairs usually observed in this genus.
Although some other species of Mecistocephalus also have 51 leg pairs, these species may be distinguished from M. evansi based on other traits. For example, like the species M. evansi, the species M. erythroceps features not only 51 leg pairs but also a bifurcated median groove on the sternites. This bifurcation is faint in M. erythroceps, however, and thus less distinct and more obscure than in M. evansi.