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

Members of the genus <i>Porcellanella</i> White, 1851 (Porcellanidae) are common commensals of sea pens in tropical and subtropical coastal waters. Despite having only three described species (<i>P. triloba</i> White, 1851 from Cape Capricorn, Australia; <i>P. picta</i> Stimpson, 1858 from Hong Kong; and <i>P. haigae</i> Sankarankutty, 1963 from the Gulf of Mannar, Indian Ocean), the taxonomy of this genus has been widely debated. <i>Porcellanella picta</i> was previously considered a junior synonym of <i>P. triloba</i>, but this synonymization has been the subject of disagreement. In this study, we conducted integrative phylogenetic and morphological analyses of <i>Porcellanella</i> specimens tentatively identified as <i>P. triloba</i>, collected from Hong Kong, Taiwan, mainland China, Thailand, Singapore and Australia. Our Maximum Likelihood and Bayesian Inference phylogenetic analyses of mitochondrial <i>COI</i> and <i>16S rRNA</i> sequences revealed four distinct lineages: one corresponding to <i>P. picta</i> from Asia, one to <i>P. triloba</i> and two representing new species (<i>P. brevidentata</i> n. sp. and <i>P. longiloba</i> n. sp.) from Australia. Morphologically, <i>Porcellanella</i> 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 <i>Porcellanella</i>. Our study demonstrates the value of an integrative approach in distinguishing cryptic invertebrate species that are considered to exhibit wide geographic distribution patterns.