-Animals (Kingdom Animalia)

-Arthropods (Phylum Arthropoda)

-Crustaceans (Subphylum Crustacea)

-Typical Crustaceans (Superclass Multicrustacea)

-Malacostracans (Class Malacostraca)

-Decapods, Isopods, and Allies (Subclass Eumalacostraca)

-Decapods and Krill (Superorder Eucarida)

-Decapods (Order Decapoda)

-Crabs, Lobsters, Shrimps, and Allies (Suborder Pleocyemata)

-True Crabs (Infraorder Brachyura)​

-Eubrachyuran Crabs (Zoosection Eubrachyura)

-Thoracotrematan Crabs (Zoosubsection Thoracotremata)

-Land, Shore, and Marsh Crabs (Superfamily Grapsoidea)

-​Land Crabs (Family Gecarcinidae)

Although they resemble true crabs, porcelain crabs are more closely related to squat lobsters and hermit crabs within the infraorder Anomura. Species in Polyonyx are typically small, flattened, and delicate, often only a few centimeters across. They have broad front claws (chelae) and a smooth to lightly sculptured carapace. Like other porcelain crabs, they possess large, feathery mouthparts (maxillipeds) used for filter feeding, which they extend into the water current to capture plankton and suspended particles.