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)

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

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