ECHINODERMATA - KU ScholarWorks - University of Kansas

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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
BLASTOID STUDIES 9 and normal to the polar axis. Inward is any direction toward the geometric center of the calyx or polar axis of the stem, and outward is any direction away from this center or axis. The oral opening is the orifice in the calyx located in the position of the mouth, and the vicinity of the oral opening may be designated as oral. This general region is also termed the summit. Any direction away from the oral opening is aboral and any direction toward this opening is termed adorai. The peristome or summit, which is the area around the mouth, comprises minute plates surrounding the mouth, as observed in some blastoids, but generally not recognized. The anal opening is an orifice laterally placed near the summit of the calyx, marking the position of the anus, and the vicinity of the anal opening is designated as anal area or anal region. Any direction toward or away from the anal opening is termed adanal or abanal, respectively. Ventral and dorsal are the same as distal and proximal, respectively, as applied to the calyx. Viewing a specimen obliquely from the oral side, and with the anal opening toward the observer, or viewing a photograph or figure of a specimen with the anal opening centrally placed on the side toward the observer, left and right sides of the specimen correspond in position to those of the observer. According to convention used by some authors, the ambulacra (and radials) are then numbered I to V in a clockwise direction, starting with I for the first ambulacrum to the left of the anal opening. Another method, introduced by Carpenter (1884) and herein used, is to letter the anterior ambulacrum (opposite the anal opening) with an "A," and proceeding in a clockwise direction, designate the other ambulacra "B," "C," "D," and "E," so that the anal opening is in the "CD" interradial area. If each plate is projected onto a flat surface in the form of a plan layout, with stem at the center, plates of the basal circlet projected radially from this center, and radials and alternating deltoids next outward from these, the anal side must be oriented away from the observer in order to preserve left and right directions in proper position. This is customary. Plan layouts are viewed from the dorsal side, and therefore the orientation of the ambulacra is opposite to that when viewed from the oral side, which results in arrangement of numbers or letters assigned to them having sequence in a counter-clockwise direction, beginning with "I" at the left of the anal opening or "A" opposite the anal opening. The position of a line extending from the centrally placed mouth to the aboral end of an ambulacrum is termed radial. Accordingly, the position of a line extending from the mouth through the mid-line of a deltoid plate, halfway between adjoining radii is called interradial. Lancets, radials, and ambulacra are radial in position and deltoids are interradial. The azygous basal is almost invariably "AB" (right anterior, or preferably anterior right) interradial in position and the other two are "DE"-"EA" (left anterior) and "BC"-"CD" (right posterior) radial in position. STEM The stem is the column that serves as means of attachment for the blastoid. It is slightly expanded at its proximal end into a thickened columnal and in some genera a definite plate or group of three plates is secreted between this columnal and the basal plates. Pentremites appears to have one supplementary or subbasal plate; Cryptoschisma has three. At the distal end of the stem, there is presumed to be an expanded, branching, treelike extension, termed the root. ETHER- IDGE & CARPENTER (1886) mention its presence in Pentremites. In adults of some genera (e.g., Eleutherocrinus, Notoblasttts, Pentephyllum, Tim oroblastus, Astrocrintts) it is quite possible that a stem is absent. The stem is composed of a regular series of discshaped columnals, circular in outline, with small radially disposed ridges (crenellae) on their distal and proximal surfaces. The crenellae extend about onethird of the distance from the periphery toward the center, which is pierced by a small round opening (lumen). More research is necessary to determine if the lumen is continuous with the body cavity and this should be investigated for each species. BASALS The basal plates form the dorsal extremity of the calyx, being attached proximally to the stem and extended distally to meet the radial plates. With the exceptions of Astrocrinus, and possibly Acentrotremites, there are invariably three basals—two large subequal plates located in the "DE"-"EA" (left anterior) and "BC"-"CD" (right posterior) radial position, and one small azygous basal, which is almost constantly in the "AB" (right anterior) interradial position. If prominent ridges are present on the basais, these have approximately the same placement in all blastoids. In the two subequal large basais, a single ridge extends from the middle of each of the three distal edges adjoining the radials to a common point in the middle of the proximal edge of the basal, thus
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