Homalozoa is an obsolete extinct subphylum of Paleozoic Era
echinoderms, prehistoric marine invertebrates. They are also referred
to as carpoids.
3 See also
Homalozoa lacked the typical pentamer body form of other
echinoderms, but all were sessile animals. Instead all Homalozoans
were markedly asymmetric, and were extremely variable in forms
The body (theca) was covered with calcite plates with a number of
openings. Their form is in some cases so unusual that it is unclear
which openings are to be considered as mouth and anus. Many of them
were stalked, similar to sea lilies (crinoids), but often their bodies
were bent over, so that the mouth and anus projected forwards rather
than upwards. Some forms, especially stylophorans, rested flat on the
In some forms the single ray (brachiole or aulacophore) possessed an
It has been claimed that some forms possessed gills and gill slits.
Homalozoans were traditionally considered to be stem-group
echinoderms, but had also been considered to lie in the stem
lineage of the chordates (calcichordates). However, it is now
generally accepted that homalozoans were echinoderms because their
calcite skeleton was composed of the typical stereom crystalline
They include the unusual stylophorans (mitrates and cornutes),
Homoiostelea (solutes), the
Homostelea (cinctans), and the
Ctenocystoidea (ctenoid-bearing homalozoans). They have recently
been recognised as a polyphyletic group. The stylophorans are now
classified as a clade of the Crinozoa, whereas the other three are
classified as clades of the Blastozoa.
Unlike many other types of echinoderm, solute homalozoans lack radial
symmetry (such as the five limbs of a starfish).  Solutes are
the sole order of the class Homoiostelea.
Solute fossils have an irregularly shaped flattened body covered in
calcite plates, and are up to about 10 cm long. The body has two
appendages, interpreted as a "feeding arm" at one end, bearing tube
feet at its end, and a "stele" at the other, which may have been used
by the animal to propel itself along the sea floor.
Imran Rahman (January–February 2009). "Making sense of carpoids".
Geology Today. 25 (1): 34–38.
^ Lefebvre, Bertrand (2003). "Functional Morphology of Stylophoran
Echinoderms". Palaeontology. 46 (3): 511–555.
^ Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA:
Holt-Saunders International. p. 1011.
^ Dominguez, Patrício; Jacobson, Antone G.; Jefferies, Richard P. S.
(2002). "Paired gill slits in a fossil with a calcite skeleton".
Nature. 417 (6891): 841–844. doi:10.1038/nature00805.
^ James W. Valentine (2004). On the origin of phyla. University
Chicago Press. 608 pp. Paperback. ISBN 0-226-84548-6. -
^ UCMP Berkeley, edu. "Echinodermata: Morphology". University of
California Museum of Paleontology. Retrieved 21 March 2011.
^ a b David, Bruno; Lefebvre, Bertrand; Mooi, Rich; Parsley, Ronald
(2000). "Are homalozoans echinoderms? An answer from the
extraxial-axial theory". Paleobiol. 26 (4): 529–555.
^ A. B. Smith Deuterostome phylogeny and the interpretation of
problematic fossil echinoderms, page 543-544 in Thomas Heinzeller,
James H. Nebelsick Echinoderms: München, CRC Press, 2004
^ Smith, A. B. (2005). "The pre-radial history of echinoderms".
Geological Journal. 40 (3): 255–280. doi:10.1002/gj.1018.
^ Henry Gee Before the backbone: views on the origin of the
vertebrates, Springer, 1996 ISBN 0-412-48300-9 page 204
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