The genus Euobrimus is a Philippines-native stick insect genus that is very similar or synonymous with the genus Brasidas.
Description
The representatives of this genus correspond to typical Obrimini in habit and resemble Obrimus species in appearance. A pair of very conspicuous holes or pits in the metasternum is characteristic of this genus. Similar metasternal pits are otherwise found only in representatives of the genus Brasidas. The males of the previously known species remain with a length of approx. significantly smaller than the females, which are long depending on the species. In egg-laying adult females, the abdomen is markedly thickened in height and width in the middle and ends in a secondary ovipositor for laying eggs. It is ventral formed from the eighth sternite, here named subgenital plate or operculum and dorsally from the eleventh tergum, which is referred to here as the supraanal plate or epiproct.
The eggs are laid in the ground by the female with the ovipositor. Typical of the eggs, which are mostly long and wide, is the bulbous, protruding dorsal area and the cover (operculum), which slopes down towards the ventral side. Due to this structure, Euobrimus eggs, like Brasidas eggs, have a clearly recognizable opercular angle.
Distribution area
For most species of the genus, the distribution area is only known through the often general indication of the type locality mentioned in the first description. Representatives of Euobrimus are mentioned from Mindanao in the region around Mount Apo and from the provinces of Surigao del Norte and Surigao del Sur, as well as from the offshore island of Siargao. On Luzon, the genus is found in the south-eastern province of Sorsogon, more precisely on Mount Pulog (not to be confused with Mount Pulag in northern Luzon), and on the offshore island of Rapu Rapu. There are also two valid species whose locality is given as Samar.
Taxonomy
In 1939 James Abram Garfield Rehn and his son John William Holman Rehn published an extensive work in which, among other genus, they established the genus Euobrimus. In this they placed two already known species that had previously been included in the genus Obrimus. They also described five new Euobrimus species, partly using juvenile type material. Euobrimus atherura, newly described on the basis of a juvenile male, was defined as the type species. The species described so far are: Euobrimus atherura Rehn & Rehn, 1939 Euobrimus bakeri Rehn & Rehn, 1939 Euobrimus cavernosus (Stål, 1877) Euobrimus cleggi Rehn & Rehn, 1939 Euobrimus dohrni Rehn & Rehn, 1939 Euobrimus hoplites Rehn & Rehn, 1939 Euobrimus lacerta (Redtenbacher, 1906) Euobrimus stephenreyesi Lit & Eusebio, 2006
The genus Brasidas, also described by Rehn and Rehn in 1939, is very similar to Euobrimus. A common autapomorphic feature is the metasternal holes or pits. While these are described as semi-bordered (“semicingulate”) in the representatives of the genus Brasidas, they are said to be more completely bordered in Euobrimus. This differentiation does not apply to the current genus assignment of the species currently held. As early as 2004, Oliver Zompro mentioned the need to conduct species-level studies to confirm the status of the genus Euobrimus or to synonymize the genus with Brasidas. Frank H. Hennemann et al. point out in 2016 that both genera are probably synonymous with each other. This assumption was supported by genetic analysis-based study by Sarah Bank et al. to clarify the phylogeny of Heteropterygidae, published in 2021. Although the examined Euobrimus and Brasidas species were found in a common clade, there are no separate clades that would justify the existence of two genera. The genus Obrimus is placed as a sister genus to the common clade of Euobrimus and Brasidas. Furthermore, according to this work, Euobrimus dohrni described by Rehn and Rehn would be a synonym of Brasidas foveolatus.