Morphological analysis of the morphologically similar genera Omalacantha and Microphrys to construct a rediagnosis for Omalacantha bicornuta

• Grant number: 25/09043-1
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: June 23, 2025
• End date: July 22, 2025
• Field of knowledge: Biological Sciences - Zoology - Taxonomy of Recent Groups
• Principal Investigator: Fernando Luis Medina Mantelatto
• Grantee: Maria Clara Gomes Petita
• Supervisor: Martha Nizinski
• Host Institution: Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (FFCLRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil
• Institution abroad: Smithsonian National Museum of Natural History, United States
• Associated to the scholarship: 24/05305-9 - Taxonomic characterization of Omalacantha bicornuta (Latreille, 1825) (Brachyura, Mithracidae): molecular and phylogeographic analyzes, BP.IC

Abstract

The Mithracidae family is a group of spider crabs consisting of 14 genera. One of them is the genus Omalacantha, which was recently revalidated and currently includes three species, which are: Omalacantha antillensis, Omalacantha interrupta and Omalacantha bicornuta. The latter is known for a considerable taxonomic history of descriptions and allocations to different genera, including Pisa, Pericera and Microphrys. This taxon was classified in Microphrys for almost two centuries with the name combination of Microphrys bicornutus. Nowadays, this genus contains five species: Microphrys weddelli, the type species, M. acuelatus, M. branchialis, M. platysoma and M. triangulatus. The classification of this species under Microphrys likely happened because this species has very similar morphological characteristics to other species of this genus. However, the specimens possess a lot of intraspecific morphological variability. Recently, using molecular analyses, Microphrys bicornutus was removed from the genus Microphrys and reallocated to the genus Omalacantha, with its name being changed to O. bicornuta. However, even though molecular data supports this new allocation, morphological data regarding the separation of these two genera is rather lacking. Additionally, our previous results show that some of the morphological characters used to distinguish Omalacantha and Microphrys are highly variable within O. bicornuta, raising questions regarding the validity of such characters for the identification of these genera and species contained within them. This major problem has led to a situation where, to understand the target species of the present study, it is necessary to analyze the target species and its closest relatives and morphologically similar taxa, including other species of genus Omalacantha and Microphrys. Using funding acquired by FAPESP, this project aims to clarify these taxonomic inconsistencies based on a more thorough morphological and possibly molecular analyses of the eight species contained in these genera that are deposited in the National Museum of Natural History.