these fossil dealer shops currently stocking crinoid and other
Echinoderms and Crinoids
echinoderms are a distinct phylum (Echinodermata meaning
spiny skin) of marine animals known from all ocean depths
that first appeared in the great diversification of life
in the early Cambrian. Among some 13,000 extinct species,
they have left a ubiquitous and prodigious fossil record.
7,000 extant species, they comprise the largest phylum not
having terrestrial and fresh water forms.
echinodermata evolved from the bilaterally symmetrical
animals (the bilateria) to have a fivefold radial symmetry
that occurs at some stage of ontogenesis or
developmental morphogenesis. This five point symmetry is
very familiar in
fully developed starfish. The vascular system of
echinoderms carry water and that in some terminate in feet
to grab and and move objects. Echinoderm reproduction proceeds
external fertilization of eggs and sperm discharged into
the water, and most undergo planktonic larval stages before
into a sessile lifestyle on the seafloor.
most beautiful echnoderm fossils correspond to four major
subphyla: 1) Blastozoa, that contains the eocrinoids, cystoids
and blastoids; 2) Asterozoa, that contains starfish and brittlestars;
3) Crinozoa, the crinoids; and 4) Echinozoa that includes
the echinoids, or sea urchins.