This World Database of all species of Kinorhyncha ever described, is part of the World Register of Marine Species (WoRMS), a global initiative to provide a register of all marine organism names. The aim of the World Kinorhyncha Database is to mirror the full hierarchical classification system of Kinorhyncha including unaccepted names and synonymy, the etymology of all scientific names, the distribution data of all published specimens including their deposition or non-deposition in which reference collection, access to molecular data, and all published references on any topic about Kinorhyncha at species level. In this way, the database will hopefully contribute to the stability of taxonomic names and facilitate information and research on all aspects of Kinorhyncha including taxonomy, phylogeny, morphology, development, biology, biogeography, ecology, and molecular biology.

Kinorhyncha (mud dragons) is a group of marine and sometimes brackish water meiofaunal animals living on algae, sea grass, kelp, on or in other invertebrates, or in sediments from the intertidal to abyssal depths. Species may occupy the surface of muddy or sandy habitats or dwell up to about one meter deep in the sediment. Kinorhyncha may represent 1–8% of the meiofauna at a given locality and in extreme cases 0.1% or 15–33%.

Whereas species with more original characters use both their head spinoscalids and their trunk for a caterpillar-like forward movement, species with more advanced characters use mainly their head spinoscalids for moving around. Kinorhynchs feed on detritus, bacteria, algae, or diatoms.

The species develop via a series of possibly six juvenile stages to the adult. The adult life history stage can moult at least once in species of a range of genera. The different adult stages may agree or disagree in their morphology. Several studies revealed considerable variation for species of several genera within populations of a sample from a single or from various locations. These more recent findings complicate identification of kinorhynchs and description of new species. It can be expected that a range of species will have to be synonymized, if a larger number of specimens will have been studied in more details.

Currently, the World Kinorhncha Database contains 307 accepted species names, the species number of all accepted and synonymized species is 546, and 619 taxonomic names of all ranks including synonyms contribute or have contributed to the classification of Kinorhyncha as a whole. The number of accepted species includes two fossil species, five taxa inquirenda and 50 species described from juvenile stages, which are usually considered as nomina dubia.

No guarantee for the correctness of the data can be given. Please inform the editor of any omissions, errors, or typos you come across, or if you need to confirm some crucial data. If you disagree with a synonym or other taxonomic decision, please send in your reasoned argument to the editor. Each contribution will be evaluated and corrections will be incorporated as quickly as possible.