Isoloida

Isoloida is a historical taxonomic term that has appeared in zoological classification as an order of crustaceans. The concept and composition of Isoloida varied among authors in the 19th and early 20th centuries, with different researchers circumscribing different sets of crustacean groups under the name. In many accounts, members described as Isoloida were small, crustacean forms with an isopod-like appearance, but there was no stable, universally accepted diagnosis.

Over time, modern systematic revisions reorganized crustacean diversity, and the rank Isoloida fell out of use. In contemporary taxonomy, Isoloida is generally regarded as obsolete, and the species once placed in it have been reassigned to other orders, notably Isopoda and Amphipoda, depending on the lineage and the evidence available. Because there is no current, widely accepted definition, Isoloida rarely appears in up-to-date databases; it is encountered mainly in historic literature and discussions of the history of crustacean classification.

The term illustrates historical efforts to classify crustaceans by morphological traits before the advent of comprehensive phylogenetic analyses. See also Isopoda, Amphipoda, Malacostraca, and broader discussions of crustacean systematics.