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Subphylum Crinozoa and Class Crinoidea |
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Most crinoids consist of a calyx
with arms supported by a stem. The arrangement of arms and
plates are the main criteria for subclass and lower
division. The arms can be single or branched, and may be
constructed of a single series of brachials (uniserial)
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The normal arrangement of plates
consist of brachials, radials, and basals. |
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Crinoids can be divided into 4
subclasses: the Inadunates, Camerates, Flexibles, and
Articulates (see your text book), only the articulates
survive to the Recent. For an example of how large crinoids
can be, look at this specimen. |
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Subphylum Blastozoa |
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The two blasotzoan classes which are of importance include the Blastoidea and Rhombifera (= cystoids of some workers). Other blastozoan classes with a fossil record include the Diploporata, and Eocrinoidea. Together, all blastozoans have hydrospires, small folds under the lancet plates. The differences between each class is based primarily upon the pore and plate arrangement. |
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Class Blastoidea |
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Blastoids were attached by a stem
to their substrate. The calyx of most species consists of 13
main plates: 5 deltoids, 5 radials, and 3 basals. Pores are
restricted to the 5 ambulacral areas covered by lancet
plates. The margins of the lancets were lined with
brachioles. The mouth is centrally located on the top of the
calyx (note Blastoids do not have a tegmen) and is
surrounded by smaller holes for water vascular control
called spiracles. |
