Echinoid Description Dictionary
by Bill Thompson www.Echinoids.com
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A 
abactinal aboral or apical aspect; side opposite mouth.
aboral located opposite to or directed away from the mouth.
aboral view view showing side of test opposite of the mouth. / dorsal
above area of test encompassing the apical system, top.
acetabulum concave proximal or articulating end of spine.
actinal oral aspect; side on which peristome is situated.
acuminate Terminal angle less than 45 degrees.  Tapering gradually to a point.
adactinal ? surface by mouth / lower side?
adapical toward the apical system.
adapical suture suture along side of coronal plate nearest mouth.
adoral toward the mouth. / located or directed toward or near the mouth.
adoral suture suture below.
adradial position corresponding to boundary between ambulacra and interambulacra.
adradial suture suture at boundary between ambulacra and interambulacra.
amb abbreviation for ambulacra
amb I amb plate next to ocular I
amb II amb plate next to ocular II
amb III amb plate next to ocular III
amb IV amb plate next to ocular IV
amb oblique Amb is slanted - not perpendicular nor parrallel.
amb V amb plate next to ocular V
ambital plates plates at the edge of test, usually the largest.
ambitus margin of test with greatest diameter. / greatest circumference.
ambulacra plural for ambulacrum.
ambulacral corresponding in position or pertaining to ambulacra
ambulacral furrow food groove.
ambulacral pore opening through ambulacral plate for passage of tube foot.
ambulacrum five pore bearing parts of test extending from apical system to peristome atternating with interambulacra.  These segments of test and their pores are part of the water vascular system. / perforations for the tube feet.
ambulacrum consists of two or a larger even number of columns of plates. / alternating with 5 interambulacra / designated by Roman numerals in Lovenian system.
amphiplacous with basicoronal interambulacral plate abutting against 2 plates adapically.
amphisternous with labrum followed by 2 large, more or less equal sternal plates opposite one another.
ampulla contractile chamber of water-vascular system internal to test, forming part of each tube foot complex; of skeleton, see camella.
ampullae plural of ampulla
anal fasciole band around the periproct./fasciole adoral and lateral to periproct; if connecting with lateral fascioles, termed lateroanal fasciole.
anal plates paired interamb plates in contact with periproct of irregular echinoids./ plates of periproctal system.
anterior toward amb III.
anterolateral toward the front
anterolateral amb the pair of ambs to the front
anus periproct.
apetaloid adapical part of amb with pores somewhat unequal in size, typically one long and one short.  Somewhat shaped like a petal of flower.
apex highest part of the test.
aphicephalous ?
apical fasciole band around the apical system.
apical plate system area of test with ocular and genital plates
apical plate system area of test with ocular and genital plates
apical scar hole in test where the apical system existed in the living echinoid.?
apical system area of test with ocular and genital plates / plates at aboral terminus of ambulacra and interambulacra including ocular and genital plates ( when present); may include one or more complemental plates.
apophyses plural of apophysis
apophysis internal projection from interambulacral basicoronal plates for attachment of muscles supporting lantern.
appendages spines
arbacoid compound plate plate with three elements of which the adapical and adoral ones are demiplates.
areole scrobicule or depression around boss for attachment of muscles controlling movement of spines.
Aristotle's lantern group of articulated plates attached to inside of mouth for chewing.  Jaws. Structure of 40 or fewer skeletal elements serving for mastication
attenuate to become thin and slender like a thread.
aulodont descriptive term for lantern with open foramen magnum and with cross section of teeth broadly U-shaped.
auricle internal process arising from basicoronal ambulacral plates for attachment of muscles supporting lantern.
author person describing the echinoid
B
base portion of spine below milled ring.
basicoronal first. / 20 plates found in the surviving row of coronal plates/ referring to corona at edge of peristome.
bead small tubercle.
below surface of fossil with the peristome, bottom.
bidentate type of pedicellaria with head consisting of 2 long pointed valves.
bigeminate having 2 pore pairs.
bilateral symmetry irregular echinoid. both sides are equal when divided from top to bottom.
biserial two longitudinal rows of pore pairs in each pore zone. / pore pair of every alternate plate slightly removed from the adradial suture.
bivium two posterior ambulacra come together in a divided apical plate system.
boss part of tubercle below mamelon shaped like truncated cone.
bottom surface of fossil with the peristome.
bourrelet bulging interamb near mouth. / externally inflated adoral part of interambulacral areas.
brace Rotula
branchia gill or respiratory organ
branchial notches gill slits at the peristome.
branchial slits gill slits at the peristome.
buccal pertaining to the mouth.
buccal membrane tissue between peristomial margin and mouth.
buccal plates plates around lantern / ten large primordial plates on buccal membrane with pores for buccal tube feet.
buccal pores pores near or in the mouth
buccal system peristomial system of plates.
buttress ridge of skeletal material extending adapically from auricle on inner surface of test.
C
caducous Falling of in any stage of development - as in apical system missing.
camarodont descriptive term for lantern with keeled teeth and closed foramen magnum.
camella pouchlike ampulla forming bulge one inner wall of the test.
camellae plural of camella
Carpenter system Ambulacral areas of test designated by capital letter (A to E) and interambulacral areas by letters of adjacent ajbulacra.
catenal plate. supplementary plate ( or plates ) along III-5 axis between anterior and posterior portions of apical system where these are disjunct.
ciliated spines very minute spines.
circlet a small circle.
claviform spines ?
clavula small ciliated spines in fascioles.
clavulae single of clavula
collar smooth tapering portion of spine located above milled ring.
compact type of apical system with no separation between anterior and posterior elements.
compass slender arched radial rod in ambulacral position at top of lantern.
complemental plate supplementary plate (or plates) in apical system.
component plate
compound plate amb plate unit composed of two or more individual plates each with two pores for tube foot, bound together by single large primary tubercle.
concave curved inward like a segment of the interior of a hollow sphere.
conjugate pores pores of a pair connected by groove in the external surface of test. / pores are usually unequal.
cordiform heart shape form
corona all amb and interamb.  All plates except for the ocular and genital plates./ principal skeletal structure excluding apical, periproctal, and peristomial systems, lantern, and appendages.
coronal plates plates of the amb and interamb.
cortex differentiated dense outer layer of spines usually bearing ornamentation./ nonliving on mature spine.
crenate crenulate
crenulate spine spine with ribbed edge./ decriptive term for tubercle or acetabulum of spine with ribbed periphery.
crenulate tubercle tubercle with ribbed edge.
cylindrical having a cylinder shape, rounded with flat top and bottom.
D
dactylous type of pedicellaria with spoon-shaped jaws mounted on individual stalks.
decoration ornamentation
demiplate amb plate which touches interamb, but not the inside amb suture. / touches adradial suture but not perradial suture.
demipyramid one of 10 elements which support teeth in aristotle's lantern.
denuded bare, bald
depressed lower than the surrounding surface.
developed visible, in detail.  Not hidden
diadematoid compound plate amb plate with three primary parts of which the middle one is largest.
diads compound plate composed of two primary plates.
dicyclic apical system with ocular and genital plates in two concentric rings.  Genitals in contact with the periproct. / exsert
dimple perforated.
diplopodus _____ arrangement. ?
discal opening apical opening.
discal region area of the apical system.
discoidal having the shape of a disk.
disjunct type of apical system with anterior part (usually genital plates 1,2,3 and 4 and ocular plates II, III, and IV ) separted from posterior part (ocular plates I and V, forms with disjunct apical system lacking genital 5.)
disjunct apical system trivium and bivium are separted by a intervening space by a variable number of narrow supplementary plates which separtate the lateral interambulacra along the anteroposterior axis.
distal end end of the spine away from the test.
domed convex, rounded on top.
dorsal aboral
dorsally situated on the back side. / dorsal / aboral
double pored two pores in sets
E
eccentric not a circular form.  Not situated in the center.
echinoid compound plate plate with three or more elements of which adoral and adapical ones are primaries and adoral one is largest. / adoral and adapical ones are primaries and adoral one is largest.
echinothurioid compound plate plate of 3 elements (primary with 2 small included plates on its adoral margin).
edge ambitus.  Margin of test with greatest diameter.
elevated above the surface of the test.
elliptical having the shape of a flattened circle.
endocyclic with periproct located within oculogenital ring.
endocylic skeleton internal?
endopetalous fasciole see internal fasciole
epiphysis element at top of Aristotle's lantern in interambulacral position.
episternal plate second pair of postlabral plates in amphisternous spatangoids.
epistroma Adventitious skeletal material on outer surface of test plates.
ethmolysian see ethmolytic
ethmolytic type of apical system in which periproct is removed from apical system and madreporite has grown backward so as to separte oculars I and V.
ethmolytic type of apical system in which genital plate 2 extends posteriorly between oculars I and II and genital 1 on one side and oculars III, IV, and V and genitals 3 and 4 on other; genital plate 5 may not be present.
ethmophract apical system condition where, madreporite is separted from oculars I and V, now in contact with each other, by the meeting of genitals 1 and 4, and the fifth genital is not replaced.
ethmophract apical system in which genital plates 1,2,3 and 4 mutually adjoin; genital plate 5 may not be present.
Euechinoidea irregular echinoid.  test with periproct located outside the oculogenital ring.
exocyclic with periproct located outside of oculogenital ring.
exsert ocular plates not toughing the edge of periproct.  Dicyclic. / only genitals are in contact with periproct.
F
fasciole narrow band of small densely packed ciliated spines (claculae) to create currents.  On test often reprsented by a groove or band of tiny tubercles. / smooth zones on the outer surface of the test.
first order tubercle primary tubercle.
flange projecting rim on a shaft.  Milled ring.
flexed bent, folded, or warped.
flexous wavy
floscelle star shaped area around peristome, formed by phyllodes and bourrelets.
food grooves narrow indentitions in the surface of the test to aid in food being transfered to the mouth, usually on the bottom. / simple or intricately branched or holes.
food grooves grooves in adoral ambulacral areas supplied with specialized tube feet for food gathering and transport; may extend into interambulacral areas and onto aboral surface.
foramen tubercle with a small depression ?
foramen magnum space between upper ends of paired demipyramids of lantern.
foremost ambulacrum amb 3
frontal sinus depressed area from the apical system to the margin in which amb III lies.
furrow dip in ridge around pore pair.
furrows groove like depressions in the test on the top or bottom.
fusiform spindle-shaped, narrowed both ways from a swollen middle.
G
genital 1 genital plate in th apical system adjacent to interamb 1
genital 2 genital plate in th apical system adjacent to interamb 2
genital 3 genital plate in th apical system adjacent to interamb 3
genital 4 genital plate in th apical system adjacent to interamb 4
genital 5 genital plate in th apical system adjacent to interamb 5
genital plate primordial interradial apical plate usually with one or more pores for discharge of genital products.
genital plates reproductive plates in the apical system.  The madreporite is perforated.  The remaining genital plates become perforate only sexual maturity. / lie in the main rays of the interambulacra.
genital pores perforations in the genital plates for discharge of reproductive products.
genitals reproductive plates in the apical system. / lie in the rays of the interambulacra.
gill slit indentations of the peristome margin in interamb for passage of stem of external branchia (gill). / crenulated margin of peristome./
girdle raised internal structures around the peristome.  Perignathic girdle.
globiferous type of pedicellaria with 3 valves containing poison glands.
globose spherical
gonad corresponds with genital pore.
gonopore see genital pore
granular zone coarse grained area / not smooth
granule small tubercle
grooves long narrow cut in the surface.  Furrows. / or ambulacral pores joined together.
H
heart urchin oblong shaped urchin.
heart-shaped irregular echinoid / bilateral symmetry / amb 3 grooved.
hemispheroida half sphere in shape.
heptagonal seven sided.
hexagonal six sided.
hexamerous symmetry equal in six parts. / partially abnormal.
holamphisternous Type of plastron having symmetrical pair of sternal plates followed by symmetrically paired but otherwise undifferentiated plates.
hydropores pores in madreporite.
hypophyllode primitive or feebly developed phyllode.
I
imbricated overlapping of plates.
imperforate no opening in tubercle.
in chevron pore pairs with a slit pattern of stripes and the each slit pointing at each other with only a slight angle.
included plates amb plates which touch neither the adradial nor the perradial suture.
inframarginal below the margin.
inner tubercles granules (small tubercles) of the amb inside of the marginal tubercles.
insert with ocular plates touching edge of periproct.
interamb abbreviated designation of interambulacrum
interamb 1 interamb on the lower left side of the bottom and extending to the top.
interamb 2 interamb on the upper left side of the bottom and extending to the top.
interamb 3 interamb on the upper right side of the bottom and extending to the top.
interamb 4 interamb on the lower right side of the bottom and extending to the top.
interamb 5 interamb on the bottom side of the bottom and extending to the top.
interambulacra plural for interambulacrum
interambulacrum five segments of the test extending from apical system to peristome, alternatin with amb.
intercalary type of apical system in which ocular plates II and IV meet at mid-line so as to separate anterior and posterior portions.
internal fasciole fasciole surrounding apical system and crossing all petals.
internal support rod-like or pillar-like structure between inner oral and inner aboral surfaces of test.
interporiferous zone area of amb between the two inner pore rows of ambulacrum.
interradial sutures sutures between columns of interamb./ suture between 2 columns of plates in interambulacrum; in forms with more than 2 columns in interambulacral area, suture between 2 middle columns.
interradials interambulacra
interradii pluarl of interradius
interradius interambulacra
irregular echinoid test with periproct located outside the oculogenital ring.
J
jaws Aristotle's lantern
K
keel raise or ridged section of corona; also longitudinal ridge on internal side of tooth.
L
labited ?
labrum somewhat enlarged, modified plilike, unpaired primordial interamb plate bordering the peristome in interambulacrum 5. / lip.
labrum plates somewhat enlarged, modified plilike, unpaired primordial interamb plate bordering the peristome in interambulacrum 5. / lip.
lamellae inside structure of the test which strengths the test.
lanceolate pore pairs with a slit pattern of a long spear.?
lateral fasciole band of tiny tubercles extending to rear from peripetalous fasciole; termed lateroanal fasciole if connected with anal fasciole.
lateroanal fasciole fasciole formed by union of lateral and anal fascioles.
lips part of the gill slits.?
longitudinal positioned or pointing across the length.
Lovenian symmetry bilateral symmetry with respect to plane passing through apical system, peristome, and periproct in irregular echinoids; recognized in regular echinoids chiefly by position of madreporite.
Lovenian system orientation of echinoids determined by madreporite being right of amb number III and in interamb number 2./ designated by Roman (I-V) and Arabic (1-5) numerals.
lower side with the peristome.
lunate peristome shaped like a crescent moon
lunule notche in the test.  Undullocation.  Notche on the margin or inside the test./ The opening is at the perradial or interradial suture.
M
madreporal plate madreporite
madreporite genital plate(s) of apical system adapted as part of water vascular madreporal plate system and identifiable as different from other genital plates by larger size and more perforation. / entrance to the ambulacral system.
madreporite genital 2: perforated with one or more hydopores./ To provide access to water-vascular system from exterior.
mamelon raised, rounded top of tubercle on which spine articulates.
mamelonated ?
mammillated dome shapped tubercles on the surface
margin edge of the test in flattened echinoids. / ambitus of corona in flattened echinoids.
marginal at the margin or edge.
marginal fasciole fasciole extending around ambitus.  masticatory apparatus.
marginal tubercles tubercles near the outside of both sides of the amb near the pores of the pore zone.
median middle
medulla meshlike central core of spines.
meridional ten areas of coronal system - 5 amb and 5 interamb.
meridoplacous with first adoral interambulacral plate abutting adapically against single plate.
meridosternous type of plastron with labrum followed by sindle large plate.
mesamphisternous plates of the plastron that are close to a mirror image of each other.
metasternous meridosternous plastron with sternal followed by several large plates in single column.
microcanal system system of canals within plates of corona for passage of secondary branches of water-vascular system leading to accessory tube feet, apparently found only in clypeasteroid echinoids.
mid-zone region of corona midway between the apical system and peristome.
miliary very small, nonprimary spine.
miliary tubercle tubercle supporting miliary spine.
militaries smaller than a primary tubercle, support for a small spine.
military tubercle smaller than a primary tubercle, support for a small spine.
milled ring flange near the base of the spine for attachment of the muscles that move the spines.
monobasal apical system where genital plates seen to fuse and ocular plates do not intervene./hydropores present over its entire area. Fused to form a single large central plate./ suture lines being obliterated.
monocyclic apical system where genital and ocular plates form a single ring around the periproct./all oculars in contact with periproct.
monoserial ____ ______ pore pairs?
multiserial pore pairs arranged in more than two longitudinal series./ type of ambulacrum with pore pairs arranged in more than 2 longitudinal series.
N
naked area of test lacking granular tubercles, usually on the bottom.
neck smooth cylindrical part of primary spine between the collar and the shaft.
neuropore a single third pore, near the pore pair.  Neuropore series for passage of a branch of the radial nerve supplying the tube foot to the exterior of the test.
node small tubercle.
nodose longitudinal ribs with small tubercles ?
nonconjugate pore pairs distinctly separated.
notch indentation of margin of test, usually at perradial suture.
notches cuts in the test.  Undullocation.  Lunules on the margins of the test.
O
oblique the shape is not perpendicular nor parrallel.? / not horizontal.
occluded plates plates in phyllode ? / amb plate which touch the perradial but not the adradial suture.
ocular I ocular I is adjacent to Amb I.
ocular II ocular II is adjacent to Amb II.
ocular III ocular III is adjacent to Amb III.
ocular IV ocular IV is adjacent to Amb IV.
ocular plates primordial plates of the apical system at the end of each amb, each perforated by an ocular pore. / lie in the main rays of the ambulcra.
ocular pore perforation in ocular plate for passage of terminal tentacle.
ocular V ocular V is adjacent to Amb V.
oculars plates of the apical system at the end of each amb, each perforated by an ocular pore. / lie in the main rays of the ambulcra.
oculogenital ring system of ocular and genital plates at apical end of amb and interamb areas, surrounding periproct in regular echinoids.
oligoporous referring to compound or pseudocompound ambulacral plate with few pore pairs, usually 3.
open not closed, as in petals of amb.
ophicephalous type of pedicellaria with jaws which lock together.
oral side of the test on which the peristome is located, usually facing down.
oral view view of the test on which the peristome is located, usually the bottom. / ventral
orbicular spherical in shape.
ornamentation patterns or ridges on the outside of a spine or tubercle.
orthosternous meridosternous plastron with sternal followed by more or less equal-sized plates in 2 columns.
oval egg shaped.Narrowing in the middle and rounded on the ends.
ovarial openings ?
ovate egg shaped
P
parapet raised edge of the platform where the mamelon sits.
pedicel tube foot / end of branch of water-vascular system serving for grasping, adhesion, locomotion, respiration, or combination of these.
pedicellaria small, pincer-like spines used for protection, grooming and the administation of food. / minute stalked specialized grasping or defensive organs articulated on granules.
pedicellariae (plural) small, pincer-like spines used for protection, grooming and the administation of food. / minute stalked specialized grasping or defensive organs articulated on granules.
pentagonal five sided.
pentameral symmetry regular echinoid / equal in all five parts.
perforated having a hole or depression in the surface. / Dimple
perforated tubercle tubercle with a small depression (also called a formen) in the top for a ligament to connect the spine with the tubercle.
perignathic girdle raised internal structures around the peristome./ continuous or discontinuous ring of internal processes around peristomial opening for attachment of muscles supporing and controlling lantern.
peripetalous fasciole band passing around petals of the amb./ fasciole passing around petals of ambulacra I,II,IV, and V and around or across ambulacral petal III.
periphery margin of the test.  Edge.  Ambitus. or edge of the apical system.
peripodium raised rim around pore pair on external surface of test.
periproct opening in the test for the anus, covered in life by a periproctal membrane and commonly plated.
periproct membrane membrane covering the opening in the test for the anus in life echinoids.
periproct system collective term for plates on periproctal membrane.
peristome opening in test for the mouth.
peristomial system mouth area, including buccal plates, up to gill slit area. / collective term for plates on buccal membrane.
perradial having meridional position at mid-line of ambulacrum.
perradial sutures sutures between two columns of amb; in forms with more than 2 columns in ambulacrum, suture between 2 middle columns.
petal adapical part of amb with pores unequal in size, typically one long and one short. / differentiated adapical segment of ambulacrum with tube feet more or less specialized for repiration.
petaloid adapical part of amb with pores unequal in size, typically one long and one short.  Shaped like the petal of a flower.
phyllode depressed area near the peristome with enlarged pores, commonly leaf shaped and part of the floscelle; in adoral portion of ambulcra.
phyllodia phyllode
pillar internal supporting columns between aboral and oral sides of test.
pillars inside structure of the test which strengths the test.
plastron bulging, expanded adoral segment of interamb number 5./ episternal plate
plate single, somewhat flattened segment of the test composed of a single calcite crystal.
platform part of tubercle, above boss, from which neck and mamelon rise.
plesiechinoid echinoid with diademoid triad-grouping occuring adoraaly and simple,nearly cidaroid plating ambitally and adapically. Reduced plates are rarely developed and invariably these are demiplates.
polyporous referring to compound or pseudocompound ambulacral plate with many pore pairs, usually 5 or more.
pore pair double perforations in the amb through which single tube foot passes./ ambulacral pore divided by wall of stereom through which single tube foot passes.
pore pairs in chevron pore pairs with a slit pattern of stripes and the each slit pointing at each other with only a slight angle.
pore zone the area of the ambs which contain the pores of the water vascular system. The pore pair area.
pores unigeminal pore pairs that become paired as one.?
poriferous zone the area of the ambs which contain the pores of the water vascular system. The pore pair area.
posterior towards interamb 5
posterolateral toward the back
posterolateral amb the pair of ambs to the back
preanal plates paired interambulacral plates between episternal and anal plates in echinoids with plastron.
primary amb plate extends across entire width of a column.
primary plate amb plate extending across entire width of plate column from perradial to adradial suture.
primary simple ?
primary spine first formed and usually largest spine of a plate, located over a growth center of the plate except on compound amb plates.
primary tubercle prominent elevation of the test for articulation of primary spine./ ontogenetically earliest.
primordial circle first formed plates situated in a row around the peristome.
primordial plates first formed plates formed following metamorphosis in each plate system, situated in a row around the peristome.
primordium earliest stages of development.
produced posteriorly prominently extended towards the back
protamphisternous type of plastron with asymmetrical pair of sternal plates followed by alternating plates.
protosternous type of plastron with labrum followed by 2 simply alternating, slightly enlarges plates.
proximal end end of spine nearest to the test.  Base.
pseudocompound plate grouping of 2 or more associated primary or reduced plates with no large primary tubercle binding the plates together.
punctate perforated.
pygasteriod echinoid with the plates simple and nearly equal throughout, but the tubercles are rhythmically arranged in triads.
pyramid large beaklike or winglike element of lantern in interambulacral position.
pyriform pear shaped
pyriform openings pear shape of pore pair openings.
pyrinid plating ?
pyrinoid type of echinoid with a demiplate inclosed between two primary plates.
R
radial ambulacral
radii define the five radii of the test at the oculars.
radiole spine
reduced plate amb plate which has lost contact with either or both of adrical or perradial sutures or both.
regular echinoid type of test having periproct within the apical system and having radial symetry./ periproct within oculogenital ring.
reproduction system area of test with ocular and genital plates
rhombic plates having the shape of an equilateral parallelogram having oblique angles.
ridge around pore pair.
ring milled ring.  Flange near the base of the spine for attachment of the muscles that move the spines.
rosette resembling a rose in shape.
rostrum raised or attenuated area of interambulacrum 5.
rotula massive radial element at top of lantern in ambulacral position.
rotulae plural of rotula
S
sand dollar flattened sea urchins.
scrobiculate tubercules microscopic tubercles around the base of the primary tubercle?
scrobicule sunken ring around the base of the tubercle for attachment of spine muscles
scutelloid having the shape of a deep bucket.?
scutum shield like
seaurchin round from above, regular echinoids.  Mouth central on bottom and anal opening exactly opposite it at the center of their upper sides.
secondaries middle sized spines.
secondary spine middle sized spine./ intermediate-sized spine, later in appearance than primary spine.
secondary tubercles middle sized tubercles./ tubercle with which secondary spine articulates.
septa radial structures external to medulla in spines.
shaft main part of the spine.
sieve plate medreporite.
simple pores pores arranged in pairs.
single pores pores not in pairs.
sinous wavy amb
sinus depressed areas from the apical system to the margin in which the ambs lie.
slit indentations of the peristome in interamb for passage of the external gill.
slit pattern the pattern of indentations of the peristome in interamb for passage of the external gill.
slits indentations of the peristome in interamb for passage of the external gill.
spheridia tiny, short spines located adorally in pits./ minute spherically modified spines on short stalks commonly situated adorally in pits near perradial suture.
spicules tiny calcareous discs or rods in body tissue, often found when sifting dirt for micro fossil material.
spine a calcareous shaft articulating on a tubercle. / a movable calcareous shaft.
spiniform Spine-like.  Composed of spines.
spinules Tiny spine like bumps - found on some spines, such as in Stereocidaris sceptrifera
spinulose provided with small spines
stellate shape of madreporite ? - not pentagonal.
stereom calcareous mesh of which skeletal elements are composed.
sternal plates first pair of postlabral plates in echinoids with plastron.
sternum plastron
stirodont descriptive term for lantern with keeled teeth and open foramen magnum.
striated
subanal fasciole oval band free of tiny tubercles on posterior, below the periproct./ enclosing more or less elliptical area on posterior face of test below periproct.
subcircular nearly round.
subglobuse nearly spherical.
subpetaloid nearly petaloid.  The ambs almost look like petals.
subspherical nearly globulose.
sulcus trough or depression in the test.
supramarginal above the margin or edge.
suranal plate large plate of periproctal system that pushes the anal opening away from the center of the periproct./ first-formed and largest plate of periproctal system, not recognizable in many echinoids.
suture line of contact between adjacent plates / narrow zone marking contact between adjacent plates; usually represented by line on surface of test.
T
terminal tentacle terminal podium of redial vessel of water-vascular system extending through ocular pore.
test shell of the urchin, five sided calcite plates./ collective term for plates of coronal, apical, periproctal and peristomial systems.
tetrabasal apical system where there exist four separate genital plates./ genital 5 not present.
tetramerous symmetry equal in four parts. / partially abnormal
tooth calcareous rod located in pyramid in interambulacral position in lantern ( upper end of tooth uncalcified).
top area of test encompassing the apical system.
traid compound plate composed of three primary plates.
transverse lying across.
trapezoidal shape with four sides with two sides parrallel.
tridenate type of pedicellaria with 3 long, pointed, jawlike valves.
trigeminate having three pore pairs.
trimerous symmetry equal in three parts. / partially abnormal
triphyllous type of minute pedicellaria with 3 leaf-like jaws not hinged to one another.