Haparoida

Haparoida is a taxonomic term that has appeared in historical classifications within the chelicerate arthropods. The exact composition and rank ascribed to Haparoida have varied among authors and periods, and in contemporary systematics there is no single, universally accepted circumscription of the group. In many current references, Haparoida is regarded as obsolete or not recognized as a distinct, natural clade.

Historically, Haparoida was used to group several lineages of small arachnids under a higher-level taxon. Because the included groups differed in composition across treatments and because the group often lacked clear diagnostic characters, later taxonomists abandoned the use of Haparoida in favor of treating its member lineages as separate clades. Molecular phylogenetic analyses conducted since the late 20th century have generally not supported Haparoida as a cohesive evolutionary unit, suggesting that any perceived similarities were due to convergence or ancestral traits that do not reflect true relationships.

In modern classifications, major chelicerate lineages such as Pycnogonida (sea spiders), Opiliones (harvestmen), Acari (mites and ticks), and Araneae (spiders) are recognized as distinct groups without a unifying Haparoida. The term may still appear in historical or paleontological discussions when referencing past classification schemes or critiquing earlier taxonomic concepts.

See also: Chelicerata, Opiliones, Acari, Araneae.