Scalidophora is a group of marine
pseudocoelomate protostomes that was proposed on morphological grounds to unite three
phyla Phyla, the plural of ''phylum'', may refer to:
* Phylum, a biological taxon between Kingdom and Class
* by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another
Phyl ...
: the
Kinorhyncha, the
Priapulida and the
Loricifera.
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.
[Heiner, I., Kristensen, R.H. 2005. Two new species of the genus ''Pliciloricus'' (Loricifera, Pliciloricidae) from the Faroe Bank, North Atlantic. Zoologischer Anzeiger. 243: 121–138.] However, the monophyly of the Scalidophora was not supported by two molecular studies, where the position of the Loricifera was uncertain
or as sister to the
Panarthropoda.
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
Ecdysozoa () is a group of protostome animals, including Arthropoda (insects, chelicerata, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo ''et al.'' in 1997, based mainly on phylogenetic tr ...
.
The two species in the genus ''
Markuelia'', known from fossilized embryos from the middle
Cambrian
The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
, are thought to be stem Scalidophorans.
The group has also been considered a single group, Cephalorhyncha,
with three classes.
The group is named after the spines (scalids) covering the introvert (head that can be retracted into the trunk).
References
Ecdysozoa taxa
Protostome unranked clades
{{Protostome-stub