ECHINODERMATA - KU ScholarWorks - University of Kansas

8 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS
one (named azygous) being almost invariably in the
same position (A-B, as subsequently explained in discussion
of orientation) in all normal blastoids. The
five elements next above the basals, each in position
of a radius extending outward from the central mouth,
are termed radials. The terminal portions (in direction
toward the stem attachment) of the five recumbent,
petal-like areas (called ambulacra) along these
radii constantly form a V-shaped indentation (termed
radial sinus) in the upper margins of the radial plates.
In the central portion of each ambulacrum there is a
spear-shaped plate (termed lancet), rarely visible on
the outer surface of the calyx but present beneath minute
plates of the ambulacral areas. Above the radials
and alternating with them are five to eight subtriangular
plates (termed deltoids, with one to six in
the anal region, each bearing special names), which
surround the oral opening. The mouth was a part of
this opening in the living animal. In the adorai parts
of the deltoids are small round to elongate openings
termed spiracles. The vault is the vertical portion
through which the ambulacra extend and the pelvis
is the vertical portion from the tip of the ambulacra
to the top of the stem. The pelvic angle is the angle
of the pelvis with center of angle at middle of the base
and sides extending upward along sides of basais and
radials to the aboral tips of the ambulacra. The basal
circlet comprises the three basal plates and the radial
circlet consists of the five radial plates. The hydrospires
are located on the radial and deltoid plates in a
position marginal to and subparallel to the ambulacra,
in general at right angles to the suture between
the radial and deltoid plates. In one group (distinguished
as an order), the hydrospires are continuous
with the spiracles and with small pores (called hydrospire
pores) which are marginal to the ambulacra.
Each ambulacrum possesses a main, centrally
placed food groove (named ambulacral groove or
main food groove), which branches laterally into
many side food grooves that extend ventrally (in direction
away from the stem) onto small thread- or cordlike,
biserially arranged appendages termed brachioles.
In the living animal, as shown by some fossils, this
system of food grooves was covered by small, alternating
cover plates adjoining the large interradial
plates (orals) which covered the mouth, centrally located
near the summit of the calyx. Between the side
food grooves are small, biserially arranged side plates,
larger ones termed primary side plates (or simply side
plates) and smaller ones (near sides of the ambulacra)
being called secondary or outer side plates. In some
genera there is a third side plate (termed inner side
plate) adjacent to the main food groove between side
plates. Medial refers to the line or direction of the
main food groove, and abmedial is away from this
line, whereas admedial is toward this line. The side
plates have a pit at the abmedial end of the side food
groove, termed brachiolar pit, with small flat areas on
each side termed brachiolar facets. A depression or
furrow is seen on many side plates, leading toward a
pore. This depression is termed a pore furrow. The
side plates bore slender, freely movable appendages,
termed brachioles. The hyprospire pores are situated
between the side plates and are never in contact with
the food grooves. It is believed that water circulated
into the pores to the hydrospires, moving upward to
the summit of the calyx and out through spiracles,
whereas food was carried downward along food
grooves of the brachioles into the side food grooves of
the ambulacrum and thence along the main food
groove upward to the mouth.
The anal opening is located on the upper half of
the calyx, between two adjacent ambulacra and to one
side of the mouth. It is larger than a spiracle and in
the living animal included the anus. The anal opening
may be excavated in a single deltoid plate (termed
anal deltoid) or it may be located between two deltoids
(an upper, termed epideltoid, and a lower, termed
hypodeltoid), or there may be three deltoids (superdeltoid
adjacent to the mouth, subdeltoid on the adoral
side of the anal opening, hypodeltoid on the aboral
side of the anal opening), or four deltoids (superdeltoid
adjacent to the oral opening, two cryptodeltoids
on either side of the anal opening, and hypodeltoid
partly covering the cryptodeltoids on the aboral
side of the anal opening).
ORIENTATION
For descriptive purposes, the following conventions
for orientation of blastoids, mostly long-established by
custom, are important. The axis extending from the
oral center to the center of the stem is designated as
the polar axis. A section parallel to this axis is a
longitudinal section, one normal to it is a transverse
section or cross section, and one tangent to the outer
surface of a blastoid is a tangential section. The direction
called proximal is defined, as in crinoids, that is,
the direction toward the point of attachment between
stem and calyx; distal is the direction upward or
downward away from this attachment. Adaxial may
be defined as any direction toward and normal to the
polar axis, and abaxial is any direction away from