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Go to the key ---INDEX---
Major Phyla
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General fossil discussion
Geologic time
Phylum ECHINODERMATA (the Echinoderms)
This phylum includes crinoids (sea lilies), blastoids, cystoids, sea
urchins, sand dollars, brittle stars, starfishes and sea cucumbers.
Despite this apparent diversity of body plans, the phylum is composed of
organisms which have pentaradial (five fold) symmetry and tube feet.
Subphylum CRINOZOA (attached echinoderms)
Within this subphylum are found all the common echinoderms of the Paleozoic,
the crinoids, blastoids and cystoids, although only crinoids survive to
this day. Most all are attached to the substrate (bottom).
From this attachment rises a columnar stem composed of stacked plates.
These stems are readily fossilized and in some areas, crinoid stems are
the main constituents of limestones. On top of this stem is the calyx,
made up of plates whose form is more or less regular, but most often shows
the typical pentaradial pattern of echinoderms.
Class CYSTOIDEA
Cystoids do not have a developed root system as do crinoids. They are
generally round to pear shaped and the plates of the calyx are irregular
in number, size and shape.
Class BLASTOIDEA
The blastoid calyx is more regular than that of cystoids. Generally,
they also have short stems. They are neither as varied or common as crinoids.
Class CRINOIDEA
They are the
most important and common class of Paleozoic echinoderms. They are attached
by a well-developed root, and the jointed stem that looks like stacked
poker chips supports a calyx with regular plates and a system of arms that
gather the food. Their appearance has earned them the common name of sea
lilies due to their superficial ressemblance to those plants. They are
clearly animals though. Additional
pictures of crinoids
Subphylum ECHINOZOA (the free echinoderms)
Class ECHINOIDEA
This class includes
the most common Mesozoic and Cenozoic echinoderms, such as sea urchins
and sand dollars. These animals are vagrant (free moving) and are
characterized by a body surrounded by spines. Earlier echinoids tend
to be regular, while later forms such as urchins, sand dollars and sea
biscuits tend to be irregular (asymmetrical). Additional
pictures of echinoids