Redescription and lectotype designation of Chasmogenus abnormalis (Sharp), with notes on its distribution

Area of Science:

• * Taxonomy and Systematics
• * Aquatic Entomology
• * Biodiversity Studies

Background:

• * Chasmogenus Sharp, 1882 is a genus of aquatic beetles in the subfamily Acidocerinae (Hydrophilidae).
• * The genus comprises 43 described species distributed worldwide, excluding the Nearctic Region.
• * Species richness is highest in the Afrotropical (18 spp.) and Neotropical (15 spp.) Regions.

Purpose of the Study:

• * To review the known species of Chasmogenus in the Oriental Region.
• * To assess the current state of knowledge regarding the genus's distribution and diversity in this region.
• * To highlight the limited number of described species and the scarcity of post-description records for Oriental Chasmogenus.

Main Methods:

• * Literature review of taxonomic and distributional data for Chasmogenus species.
• * Analysis of existing scientific records and museum collections (if applicable, though not explicitly stated in abstract).
• * Comparison of species richness across different zoogeographic regions.

Main Results:

• * Only four Chasmogenus species have been described from the Oriental Region: C. abnormalis, C. rubricollis, C. larsi, and C. cattienus.
• * Among these, only C. abnormalis has been recorded more than once since its initial description.
• * This indicates a significant gap in the understanding of Chasmogenus diversity and distribution in the Oriental Region.

Conclusions:

• * The Oriental Region is significantly underrepresented in described Chasmogenus species compared to other major zoogeographic areas.
• * Further taxonomic and faunistic research is crucial to accurately assess the biodiversity of Chasmogenus in the Oriental Region.
• * The limited records suggest potential under-discovery or under-reporting of these aquatic beetles.