Integrative Phylogenetic and Morphological Analyses Reveal Two New Species of Porcellanid Crabs and Resurrect Porcellanella picta Stimpson, 1858 (Decapoda: Porcellanidae)

Members of the genus Porcellanella White, 1851 (Porcellanidae) are common commensals of sea pens in tropical and subtropical coastal waters. Despite having only three described species (P. triloba White, 1851 from Cape Capricorn, Australia; P. picta Stimpson, 1858 from Hong Kong; and P. haigae Sankarankutty, 1963 from the Gulf of Mannar, Indian Ocean), the taxonomy of this genus has been widely debated. Porcellanella picta was previously considered a junior synonym of P. triloba, but this synonymization has been the subject of disagreement. In this study, we conducted integrative phylogenetic and morphological analyses of Porcellanella specimens tentatively identified as P. triloba, collected from Hong Kong, Taiwan, mainland China, Thailand, Singapore and Australia. Our Maximum Likelihood and Bayesian Inference phylogenetic analyses of mitochondrial COI and 16S rRNA sequences revealed four distinct lineages: one corresponding to P. picta from Asia, one to P. triloba and two representing new species (P. brevidentata n. sp. and P. longiloba n. sp.) from Australia. Morphologically, Porcellanella species can be distinguished by the colour markings on the chelipeds and carapace, the shape of the trilobate rostrum, the presence or absence of a meral lobe on the cheliped, the relative size of the unguicles on the ambulatory leg dactylus, and the presence or absence of a spinule on the lateral margin of the pterygostomian flap. We provide a morphological key to the species of Porcellanella. Our study demonstrates the value of an integrative approach in distinguishing cryptic invertebrate species that are considered to exhibit wide geographic distribution patterns.