Soluta is an extinct class of
echinoderms that lived from the Middle Cambrian to the Early Devonian.
[ The class is also known by its junior synonym Homoiostelea. Soluta is one of the four "carpoid" classes, alongside Ctenocystoidea, ]Cincta
Cincta is an extinct class of echinoderms that lived only in the Middle Cambrian epoch. Homostelea is a junior synonym. The classification of cinctans is controversial, but they are probably part of the echinoderm stem group.
Cinctans were sessi ...
, and Stylophora
The stylophorans are an extinct, possibly polyphyletic group allied to the Paleozoic Era echinoderms, comprising the prehistoric cornutes and mitrates. It is synonymous with the subphylum Calcichordata. Their unusual appearances have led to a va ...
, which made up the obsolete subphylum Homalozoa. Solutes (or solutans) were asymmetric animals with a stereom
Stereom is a calcium carbonate material that makes up the internal skeletons found in all echinoderms, both living and fossilized forms. It is a sponge-like porous structure which, in a sea urchin may be 50% by volume living cells, and the rest b ...
skeleton and two appendages, an arm extending anteriorly and a posterior appendage called a homoiostele.
Biology
Most solutes were free-living, but the basal solutan ''Coleicarpus'' used its homoiostele as a holdfast, as did juvenile ''Castericystis''.[
]
Classification
The phylogenetic position of Soluta is contentious. Solutans are widely agreed to be echinoderms, though the outmoded[ ]calcichordate hypothesis The calcichordate hypothesis holds that each separate lineage of chordate (Cephalochordates, Urochordates, Craniates) evolved from its own lineage of mitrate, and thus the echinoderms and the chordates are sister groups, with the hemichordates as an ...
held that they were ancestral to both echinoderms and chordates
A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These five ...
.[ Within echinoderms, one hypothesis holds that stylophorans are stem-group echinoderms which branched off before echinoderms evolved radial symmetry.][ Another hypothesis holds that they are specialized descendants of radiate echinoderms which lost radial symmetry, likely belonging to Blastozoa.][
Solutes are divided into two orders, Syringocrinida and Dendrocystitida.][
]
Distribution
The earliest solutes, ''Coleicarpus'' and ''Castericystis'', lived during the Drumian age of the Cambrian.[ Solutes were the last of the four carpoid classes to appear in the fossil record. Solutes appear to have evolved in Laurentia,][ but became more widespread during the Ordovician.][
]
References
Homalozoa
Paleozoic echinoderms
Prehistoric deuterostome classes
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