Cystoidea
Cystoidea (cystoids; subphylum Blastozoa, phylum Echinodermata) Extinct group of echinoderms, ranking in some classification schemes as a class or superclass, and ranging from the Lower Ordovician to the Upper Devonian. The body is spherical or ovoid, covered with a plated theca, and was usually attached to the substratum either directly or by a short stalk. The thecal plates are calcitic and perforated by characteristic pore structures that functioned in respiration. The plates are arranged in circlets but vary in number from around 13 to more than 100, giving an irregular appearance. The mouth, on the upper surface, is surrounded by ambulacral food grooves that in some cystoids were equipped with food gathering appendages called brachioles. These are rarely preserved. In many cases radial symmetry is poorly developed.
More From encyclopedia.com
Blastozoa , Blastozoa (phylum Echinodermata) Subphylum of extinct, stalked echinoderms, ranging from the Silurian to the Permian. The stem (rarely preserved) was… Upper , up·per1 / ˈəpər/ • adj. 1. situated above another part: his upper arm the upper atmosphere. ∎ higher in position or status: the upper end of the soci… Oppel zone , Oppel zone A concurrent range zone as originally conceived by Albert Oppel. The lower boundary of the zone is usually determined by the first appeara… Crinoids , Crinoidea (crinoids; subphylum Crinozoa; phylum Echinodermata) The most primitive living class of echinoderms, whose members are either stalked (sea… Upper Class , upper class Conventionally the upper class is often thought of as equivalent to the ‘aristocracy’: that is, the (often hereditary) noble class, compr… Preserving , PRESERVING. Food preservation conserves food for future use. Most of the basic processes have been employed throughout the world for millennia. The p…
You Might Also Like
NEARBY TERMS
Cystoidea