Soluta is an extinct class of
echinoderms that lived from the Middle Cambrian to the Early Devonian.[1] The class is also known by its junior synonym Homoiostelea. Soluta is one of the four "carpoid" classes, alongside
Ctenocystoidea,
Cincta, and
Stylophora, which made up the obsolete subphylum
Homalozoa. Solutes (or solutans) were asymmetric animals with a
stereom 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.[2][3]
The phylogenetic position of Soluta is contentious. Solutans are widely agreed to be echinoderms, though the outmoded[5]calcichordate hypothesis held that they were ancestral to both echinoderms and
chordates.[6] Within echinoderms, one hypothesis holds that stylophorans are
stem-group echinoderms which branched off before echinoderms evolved
radial symmetry.[7] Another hypothesis holds that they are specialized descendants of radiate echinoderms which lost radial symmetry, likely belonging to
Blastozoa.[8]
Solutes are divided into two orders, Syringocrinida and Dendrocystitida.[9]
Distribution
The earliest solutes, Coleicarpus and Castericystis, lived during the
Drumian age of the Cambrian.[3] Solutes were the last of the four
carpoid classes to appear in the fossil record. Solutes appear to have evolved in
Laurentia,[3] but became more widespread during the Ordovician.[10]
References
^Lefebvre, Bertrand; Derstler, Kraig; Sumrall, Colin D. (2012). "A reinterpretation of the solutan Plasiacystis mobilis (Echinodermata) from the Middle Ordovician of Bohemia". Zoosymposia. 7: 287–306.
doi:
10.11646/zoosymposia.7.1.27.
^Jefferies, R. P. S. (1990). "The solute Dendrocystites scoticus from the Upper Ordovician of Scotland and the ancestry of chordates and echinoderms". Palaeontology. 33 (3): 631–679.