ECHINODERMATA

Exclusively Marine

Asteroids -sea stars
Ophiuroids - Brittle stars

Echinoids - sand dollars and sea urchins
Holothuroids - sea cucumbers
Crinoids - sea lilies (attached) or feather stars (free-swimming)
Blastoids
Cystoids

Primitive bilateral symmetry     
Radial symmetry with a fivefold plan of organization (pentameral symmetry)
Calcite - Single crystals for each plate
Skeleton the product of internal secretion, individual hard
Parts can grow in size as the animal grows.
Theca - calyx - test
Appendages - rays, arms, stem

Calcareous parts have a microstructure in which regularly arranged minute passageways permeate the calcite - fine honeycomb structure.

SUBPHYLUM ECHINOZOA       
Class Edrioasteroidea: Edrioasteroids ancestral sea stars (?)
Often attached to hard ground or benthonic organisms discoid, globose body
Flexible theca composed of many small irregularly polygonal or rounded plates Mouth on upper surface, anus lateral on upper surface 5 straight or curved ambulacral areas extend toward borders of the theca Early Cambrian -- Middle Pennsylvanian

Class Holothuroidea
Marine, generally benthonic
Mouth encircled by tentacles at one end
Microscopic calcareous sclerites embedded in body wall
Rarely preserved, but their fecal pellets are widespread
Cambrian (?) Ordovician - Holocene,

Class Echinoidea - Echinoids -Sea Urchins -
Heart Urchins
Sand dollars
Rigid exoskeleton test made up of interlocking plates   
Some burrow, some bore
Classification based on form, teeth, solid or hollow spines, test flexible or rigid
Ordovician -- Holocene

REGULAR echinoids: most common sea urchins
circular test, nearly perfect pentameral symmetry
anus located centrally on upper surface
spines generally long
all have an Aristotle's lantern "teeth-holding structure"
all Paleozoic echinoids were regular IRREGULAR echinoids: includes sand dollars
elongated test
anus outside and generally posterior to mouth
each ambulacrum and interambulacrum has two columns of plates - posterior interambulacrum differs from others

SUBPHYLUM CRINOZOA

Class Crinoidea: Crinoids
Pentamerous crinozoans
commonly with long stalk, some free-living, a few sessile unstalked cuplike theca composed of a regular pattern of calcareous plates arranged in cycles
theca ovoid to spheroid, conical, subcylindrical Tegmen (flexible ceiling or dome) over the calyx upper surface contains mouth and anus Arm number varies with temperature: warm water - many arms colder water - depth - fewer arms
entire portion of the calyx above the stem, including arms, is termed the crown. holdfast anchors the crinoid
columnals often contain lateral or central hole(s) - lumen Fig. 18.31 cirrus (arms) often extend from columnal   Fig. 18.31 line between columnals - suture lateral attachment "knobs" - cirrus scar" Middle Cambrian - Holocene

structure of the brachioles (arms), nature of the tegmen Inadunates: Fig. 18.27; 18.28; 18.33 A & D largest group of Paleozoic crinoids cylindrical to bowl-shaped calyx monocyclic (one circlet of plates below the plates bearing the brachials) or dicyclic (two circlets of plates below the plates bearing the brachials) calyx simple, lightly plated tegmen primitive uniserial free arms that may become biserial and  pinnulate single small columnals often with cirri Early Ordovician to Middle Triassic

Camerates: Fig. 18.33 B & C
large conical or globose calyx
monocyclic or dicyclic calyx
firmly joined plates
fixed brachials and interbrachials incorporated into the top of the cup
heavily plated tegmen
uni serial or biserial arms bearing pinnules
stem with one-piece columnals, usually with cirri
Early Ordovician to Late Permian - common in Silurian & Mississippian Flexibles: Fig. 18.33E
conical to bowl-shaped dicyclic calyx
loosely sutured plates
lower arms and interbrachials incorporated into the top of the calyx
flexible tegmen with many small plates
uni serial arms lacking pinnules
circular one-piece columnals lacking cirri
Middle Ordovician to Late Permian - common in Silurian Articulates: Fig. 18.33 F & G
modern crinoids
reduced dicylcic cup
unplated or lightly plated tegmen
arms usually long and uniserial, branch on second brachial
many pinnules
stems circular to pentagonal with cirri, or with cirri attached to a fused circular plate
Triassic to Holocene Class Paracrinoidea Fig; 18.35 (rare)
lens-shaped to globular theca
asymmetrical recumbent ambulacra with erect uniserial pinnules, or asymmetrical erect, uniserial arms
stem usually curved near theca
columnal attached to three basal plates of calyx
Early Ordovician to Early Silurian

SUBPHYLUM BLASTOIDEA
Class Diploporita: Cystoids
anchored or attached plated theca, plates arranged in circles with ambulacra and biserial arms Early Ordovician - Early Devonian Class Blastoidea: Blastoids
excellent pentameral symmetry
no arms, stalked
Ordovician (?) Silurian to Permian

SUBPHYLUM ASTEROZOA      Fig 18.1 B & E; 18.15 Ordovician to Holocene Class Asteroidea - Sea stars

Class Ophiuroidea - Brittle stars