Pruulida

Pruulida is a genus of small, shelled arthropods first described in 1923 by the Austrian zoologist Karl Friedrich Schmidt in his work on the Meiofauna of the North Atlantic. The genus is placed within the class Tardigrada, order Parachela, and family Pruulidae, a group that is distinguished by its unique dorsal cuticle ornamentation and the presence of an ectopodial paddle structure. Species of Pruulida are typically found in marine and brackish sediments, ranging from the temperate waters of the Azores to the subpolar regions of the Norwegian Sea. They are benthic users of the interstitial water film, living in the spaces between sand grains.

Morphologically, Pruulida species possess a generally oval body shape, with a dorsal plate that features a series of platelets arranged in a concentric fashion. The cuticle is noted for its finely ridged microstructure, which is believed to aid in locomotion through viscous environments. Each individual has four pairs of legs, each bearing two highly modified claw structures. The reproductive system of Pruulida is ovoviviparous; females carry embryos within a pouch before giving birth to fully formed juveniles. Genetic studies that have sampled mitochondrial COI and nuclear 18S rRNA genes show that Pruulida forms a distinct clade within Parachela, but the phylogenetic position of the family Pruulidae remains unresolved in the broader tardigrade tree. The genus is relatively species-poor, currently comprising three recognized species: Pruulida marina, Pruulida borealis, and Pruulida alpina, each differentiated by subtle morphological traits and geographic distribution.