Kinorhyncha

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Kinorhyncha Temporal range: Early Cambrian–Recent[1] PreꞒ Ꞓ O S D C P T J K Pg N
Echinoderes hwiiza
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Clade:	Bilateria
Clade:	Nephrozoa
(unranked):	Protostomia
Superphylum:	Ecdysozoa
Clade:	Scalidophora
Phylum:	Kinorhyncha Reinhard, 1881
Orders
See text

Kinorhyncha

Kinorhynchs eat either

There are two sexes that look alike, although some sexual dimorphism in allometry has been reported.^[6] A pair of gonads are located in the mid-region of the trunk, and open to pores in the final segment. In most species, the sperm duct includes two or three spiny structures that presumably aid in copulation, although the details are unknown. Individual spermatozoa can reach a quarter of the total body length.^[7] The larvae are free-living, but little else is known of their reproductive process.^[5] After having laid an egg, the female packs it into a protective envelope of mud and organic material.^[8]

Classification

Their closest relatives are thought to be the phyla Loricifera and Priapulida. Together they constitute the Scalidophora.

Taxonomy

The two groups of Kinorhynchs are generally characterized as classes in Sørensen et al. (2015).^[9] 270 species have been described and this number is expected to increase substantially.^[10][11] Morphological data has been collected for systematic phylogeny from dozens, and the integration of this with molecular data has led to a new systematic paradigm featuring the order Allomalorhagida (with Homalorhagida being retired).^[9] Phylogenomic data has shown Allomalorhagida and Cyclorhagida to be divided in three and two major clades respectively.^[12]

The oldest known species is Eokinorhynchus from the Fortunian of China.^[13]

Phylum Kinorhyncha

• Class Cyclorhagida (Zelinka, 1896) Chitwood, 1951
  • Order
    Echinorhagata
    Sørensen et al., 2015
    • Echinoderidae Zelinka, 1894
  • Order Kentrorhagata Sørensen et al., 2015
    • Antygomonidae
      Adrianov & Malakhov, 1994
    • Cateriidae
      ? Gerlach, 1956 (following Sørensen et al.)
    • Centroderidae Zelinka, 1896
    • Semnoderidae Remane, 1929
    • Zelinkaderidae Higgins, 1990
  • Order Xenosomata Zelinka, 1907
    • Campyloderidae Remane, 1929
• Class Allomalorhagida Sørensen et al., 2015
  • Pycnophyidae Zelinka, 1986
  • Order Anomoirhaga Herranz et al., 2022
    • Cateriidae
      ? Gerlach, 1956 (following Herranz et al.)
    • Dracoderidae Higgins & Shirayama, 1990
    • Franciscideridae Sørensen et al., 2015
    • Neocentrophyidae Higgins, 1969

References