Page 405 - Introduction to Paleobiology and The Fossil Record

392 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Class PARACRINOIDEA
• Irregularly arranged plates comprising globular to lenticular theca; 2–5 ambulacra commonly
with pinnules. Hydropore adjacent to mouth. Stem attached to three basal plates
• Ordovician (Darriwilian to Hirnantian)

Class BLASTOIDEA
• Flask-shaped theca commonly with three basal plates; ambulacra with elongate lancet plate and
rows of side plates
• Ordovician (Katian) to Permian (Tatarian)

Class DIPLOPORITA
• Globular theca with many plates in an irregular to regular pattern; 3–5 food grooves with
brachioles. Diplopores perforate thecal plates
• Cambrian (Middle) to Devonian (Eifelian)

Class RHOMBIFERA
• Globular theca with 2–5 ambulacra extending from the mouth to, commonly, the edge of the
upper surface. Pore structures cross adjacent thecal plates arranged in a rhomboid pattern, and
comprise the respiratory system
• Cambrian (Upper) to Devonian (Frasnian)

Class CRINOIDEA
• Calyx with lower cup and upper tegmen. Sea lilies and feather stars
• Ordovician (Tremadocian) to Recent.

Subphylum ELEUTHEROZOA
Class EDRIOASTEROIDEA
• Disk-shaped thecae with straight or curved ambulacra with the mouth situated centrally and the
anus sited on the interambulacra
• ?Precambrian (Ediacaran), Cambrian (Lower) to Carboniferous (Gzelian)
Class ASTEROIDEA

• Between 5 and 25 arms with large tube feet extend from a central disk. Starfishes or sea stars
• Ordovician (Floian) to Recent
Class OPHIUROIDEA

• Five long, thin, fl exible arms, consisting of vertebrae and with small tube feet, extend from large,
circular central disk. Brittle stars or basket stars
• Ordovician (Floian) to Recent
Class ECHINOIDEA

• Test is usually globular with plates differentiated into ambulacral and interambulacral areas.
Mouth on underside, anus on upperside or sited posteriorly. Sea urchins, heart urchins and sand
dollars
• Ordovician (Katian) to Recent

Class HOLOTHUROIDEA
• Body is cucumber-shaped with leathery skin with muscular mesoderm and spicules. A ring of

modified tube feet surround the mouth. Sea cucumbers
• Ordovician (Floian) to Recent