An internal flange that originated from the basicoronal plate in interambulacrum 3 and is associated with supporting the pharynx in atelostomates. Picture shows the inside of a broken test in oblique view.
Specialized flattened spines that form a protective pallisade around the base of primary spines and cover their muscle ring.
A small tubercle immediately surrounding the primary tubercle and bearing a specialized flattened spine that protects the muscle of the adjacent primary spine.
A ring of differentiated small tubercles surrounding the primary tubercle and bearing specialized flattened spines that protect the muscle of the adjacent primary spine.
A spine attached to mamelonate tubercles on ambulacral or interambulacral plates which flank the primary spine and tubercle.
A smaller tubercle flanking the primary tubercle.
A compound ambulacral plate composed of three elements of which only two are united by an overlying tubercle: the third element is simple. This is also known as acrosaleniid plate compounding.
A compact apical disc in which genital plate 2 is extended posteriorly between the posterior genital (G1, G4) but not between the posterior ocular (OI, OV) plates.
The part of a spine that lies distal to the basal attachment
simple (ambulacral plate)
An ambulacral plate that corresponds to a single element. Each succesive plate bears its own primary tubercle in a column.
A spine with a shaft that ends distally in an expanded and flattened tip.
A pit on ambulacral plates in which the sphaeridium sits. These may be perradial or positioned close to the ambulacral pores and are usually developed only on plates close to the peristome.
A microscopic, highly modified glandiform spine used for sensing body orientation. Sphaeridia are present in all but the cidaroids and are mostly confined to the adoral region of ambulacra. Oral area of a spatangoid shown with basicoronal plates in blue
An articulated appendage used for defence or locomotion.
The term applied to the microstructure of the plate, in which calcite is deposited as an interconnected meshwork of rods.
Plates 2a and 2b (purple) in the posterior interambulacrum of atelostomate echinoids . These are the first pair of plates following the labral plate (red) and are often enlarged to form much of the posterior oral surface. These plates usually bear locomotory spines.
An ovate, bilobed or shield-shaped fasciole near the base of the posterior face beneath the periproct.
A projecting region at the base of the posterior face beneath the periproct.
subanal tube feet/pores
Specialized tube-feet/pores arising from the inner columns of ambulacral plates at the angle between the oral and posterior face. These are present only in Atelostomata and used for building a sanitary funnel in burrowing urchins.
The distal disc of a tube-foot, supported by a rosette of plates and used for adhesion. The phtograph shows the tube feet suckers clearly, attached to a glass plate.
A concave ambulacrum forming a furrow over the test. Usually refers to the anterior ambulacrum in spatangoids and holasteroids.
An enlarged periproctal plate. In saleniids the suranal plate(s) form an integral part of the apical disc. In Echinoida they are present only in early development.
Deep pits usually positioned at the junction of three plate sutures on the exterior of the test (arrowed). Their function is unknown.
The boundary between two adjacent abutting plates of the test.