The kinorhynchs (mud dragons) are a small phylum of microscopic, free‐living, segmented acoelomate or pseudocoelomate invertebrates belonging exclusively to the marine meiofauna. Some 150 species have been described from polar to tropical environments. The kinorhynchs have their phylum, but they are related to the phyla Loricifera and Priapulida. Cambrian microfossils may belong to the stemgroup of both Kinorhyncha and Priapulida.

Keywords: Aschelminthes; Cambrian microfossils; ecdysozoa; meiofauna; muddy sediments; 18S rRNA genes

Figure 1.

Morphology of the Arctic kinorhynch Echinoderes aquilonius. (a) Ventral view of a female. Note that the head and the mouth cone are fully extruded. (b) Dorsal view of a female. Note that the head is retracted and the neck (pl) forms a closing apparatus. Abbreviations: ag, adhesive gland; as, lateral terminal accessory spine; br, brain; D‐10, dorsal spine; dg, dorsal gland; gp, pore of mucous gland; go, gonopore; gu, midgut; L‐11, lateral spine; Lt, lateral terminal spine; mg, mucous gland; Nc, nephridiopore; os, oral style; ov, ovarium; ph, pharyngeal bulb; pl, placid of the neck; pr, protonephridium; re, rectum; si; sieve plate; sr; seminal receptacle; S‐3 to S‐13, trunk segments; ss; spinoscalid; ts, trichoscalids. (Modified from Kristensen and Hay‐Schmidt, 1989; drawn by Beth Beyerholm.)

Figure 2.

Simplified cladogram of the phylum Kinorhyncha showing the orders, suborders and families. The schematic representation is based on the classification system of Higgins (1990), but new data are added in the cladogram.


Further Reading

Aguinaldo AMA, Turbeville LS, Linford LS et al. (1997) Evidence for a clade of nematodes, arthropodes, and other molting animals. Nature 387: 489–493.

Brown R (1983) Spermatophore transfer and subsequent sperm development in a homalorhagid kinorhynch. Zoologica Scripta 12: 257–266.

Conway Morris S (1977) Fossil priapulid worms. Special Papers in Palaeontology 20: 1–95.

Higgins RP (1971) A historical overview of kinorhynch research. In: Hulings NC (ed.) Proceedings of the First International Conference on Meiofauna, pp. 25–31. Smithsonian Contributions to Zoology, vol. 76.

Higgins RP (1974) Kinorhyncha. In: Giese AC and Pearse JS (eds) Reproduction of Marine Invertebrates, pp. 507–518. New York: Academic Press.

Higgins RP (1983) The Atlantic barrier reef ecosystem at Carrie Bow Cay, Belize, II: Kinorhyncha. Smithsonian Contributions to Marine Sciences 18: 1–131.

Higgins RP (1990) Zelinkaderidae, a new family of cyclorhagid Kinorhyncha. Smithsonian Contributions to Zoology 500: 1–26.

Kristensen RM and Hay‐Schmidt A (1989) The protonephridia of the Arctic kinorhynch Echinoderes aquilonius (Cycloharida, Echinoderidae). Acta Zoologica (Stockholm) 70: 13–27.

Kristensen RM and Higgins RP (1991) Kinorhyncha. In: Harrison FW and Ruppert EE (eds) Microscopic Anatomy of Invertebrates, Volume 4: Aschelminthes, pp. 377–404. New York: Wiley‐Liss.

Müller KJ and Hinz‐Schallreuter I (1993) Palaeoscolecid worms from the Middle Cambrian of Australia. Palaeontology 36: 549–592.

Nebelsick M (1993) Introvert, mouth cone, and nervous system of Echinoderes capitatus (Kinorhyncha, Cyclorhagida) and implications for the phylogenetic relationships of the Kinorhyncha. Zoomorphology 113: 211–232.

Neuhaus B (1994) Ultrastructure of alimentary canal and body cavity, ground pattern, and phylogenetic relationships of the Kinorhyncha. Microfauna Marina 9: 61–156.

Neuhaus B (1995) Postembryonic development of Paracentrophyes praedictus (Homalorharida): neoteny questionable among the Kinorhyncha. Zoologica Scripta 24: 179–192.

Walossek D and Müller KJ (1997) Cambrian “Orsten”‐type arthropods and the phylogeny of Crustacea. In: Fortey RA and Thomas RH (eds) Arthropod Relationships, pp. 139–153. Systematics Association Special Volume Series, vol. 55.

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How to Cite close
Kristensen, Reinhardt Møbjerg(May 2001) Kinorhyncha. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001590]