Squat lobsters (family Galatheidae Samouelle, 1819) inhabiting shallow reefs are small crustaceans that can exhibit bright colors and include many cryptic species. Despite being a group with active taxonomists, basic details on their natural history, population structure, ecological associations, and even live coloration patterns remain largely unknown for many species. After a 2-week expedition aimed to conduct general collections of crustaceans from Guam, we recorded several new galatheids, including two new species. We sequenced the universal barcode region of the mitochondrial gene COI using Oxford Nanopore Technology to study the molecular diversity of squat lobsters in Guam and to detect potential species complexes across the Central Pacific. As a result, we describe the two new species, Coralliogalathea viridis Rodríguez-Flores & Giribet sp. nov. and Galathea calcifer Rodríguez-Flores & Giribet sp. nov., and provide new records and new data on the phylogenetic relationships, natural history, coloration patterns, geographic distribution, and biological associations of a total of ten species of galatheid squat lobsters.
