On the identities of three common shallow-water swimming crabs Portunus hastatoides Fabricius, 1798, P. Dayawanensis Chen, 1986, and P. pseudohastatoides Yang and Tang, 2006 (Crustacea: Decapoda: Portunidae): Essentials for benthic ecological monitoring and biodiversity studies

The portunid crab Portunus hastatoides Fabricius, 1798, is a widely distributed common deposit feeder in sandy and muddy subtidal ecosystems in Indo-Pacific waters and has been frequently used as an indicator species in ecological monitoring studies. The identifcation of P. hastatoides in many previous monitoring studies was somewhat ambiguous and likely confused by the coexistence of other morphologically similar species (i.e., P. dayawanensis Chen, 1986, and P. pseudohastatoides Yang and Tang, 2006), which were often misidentifed as P. hastatoides. Correct species identification is crucial to generate accurate results from ecological monitoring and biodiversity surveys. In this paper, we redescribe the diagnostic features of these 3 morphologically similar species, P. hastatoides (but see below), P. dayawanensis, and P. pseudohastatoides in Hong Kong and Taiwanese waters and provide a refned species identifcation guide for benthic ecologists and environmental protection authorities. In the present study, we also found that P. hastatoides in Hong Kong and Taiwan morphologically differed from one of the types of P. hastatoides (from the Indian Ocean), suggesting the presence of a cryptic species complex. Before any extensive revisions are made on the group, we continue to refer to the Hong Kong and Taiwanese populations as P. hastatoides. Crab specimens were trawled from marine environments within the Taiwan Strait where these 3 Portunus species are common. Key features of each of these species were identified; these included the morphology of the carapace frontal teeth and male 1st pleopod.