Trechus from Ethiopia with Aedeagus Right Side Superior in Repose, an Unusual Character State in Trechine Beetles (Coleoptera: Carabidae)

The Miocene volcano Mt. Choke in northern Ethiopia is known for its very species-rich <i>Trechus</i> fauna. In addition, the enormous morphological diversity that is expressed within a single subgenus, <i>Abyssinotus</i>, which is endemic to northern Ethiopia, is unique within the global <i>Trechus</i> fauna. In this paper, we describe eight additional new species and three subspecies of the <i>Trechus</i> subgenus <i>Abyssinotus</i>, all of which are endemic to Mt. Choke. These species belong to two different lineages within <i>Abyssinotus</i>, each differing from other lineages of the subgenus by certain morphological character states described in this paper and alternatively named the <i>T. lobeliae</i> and the <i>T. basilewskianus</i> subgroups. Several species of these subgroups are characterised by an apomorphical inverse male genital, with the right side up in repose. The <i>T. lobeliae</i> subgroup comprises two species and is monomorphic with respect to this character. The <i>T. basilewskianus</i> subgroup comprises eight species, including six species with monomorphically inverse male genitalia and two species with male genitalia monomorphically in the 'normal' position. These are the first examples within Trechinae in which inverse male genitalia are a species- or even group-specific characteristic. A brief summary of the distribution of this trait within the Carabidae is provided. We also present a new identification key for the <i>Trechus</i> species known so far from Mt. Choke.