Scalidophora
Proposed taxonomic clade / From Wikipedia, the free encyclopedia
Scalidophora is a group of marine pseudocoelomate protostomes that was proposed on morphological grounds to unite three phyla: the Kinorhyncha, the Priapulida and the Loricifera.[2][3] The three phyla have four characters in common — chitinous cuticle that is moulted, rings of scalids on the introvert, flosculi, and two rings of introvert retracts.[4] The introvert and abdomen are separated by a distinct neck region in all groups, but in adult macroscopic priapulids it becomes rudimentary in Priapulus and is completely absent in Halicryptus.[5] However, the monophyly of the Scalidophora was not supported by two molecular studies, where the position of the Loricifera was uncertain[2] or as sister to the Panarthropoda.[3] Both studies supported a reduced Scalidophora comprising the Kinorhyncha and Priapulida as sister phyla. Their closest relatives are the Panarthropoda, Nematoda and Nematomorpha; thus, they are placed in the group Ecdysozoa.
Scalidophora | |
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Ottoia prolifica from the Walcott Quarry of the Burgess Shale (Middle Cambrian) near Field, British Columbia, Canada. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Subkingdom: | Eumetazoa |
Clade: | ParaHoxozoa |
Clade: | Bilateria |
Clade: | Nephrozoa |
(unranked): | Protostomia |
Superphylum: | Ecdysozoa |
Clade: | Scalidophora Lemburg, 1995 |
Phyla | |
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Synonyms | |
Cephalorhyncha, Priapozoa |
The two species in the genus Markuelia, known from fossilized embryos from the middle Cambrian, are thought to be stem scalidophorans.
The group has also been considered a single group, Cephalorhyncha,[6] with three classes.
The group is named after the spines (scalids) covering the introvert (head that can be retracted into the trunk).[7]