?Early Ordovician, Middle Ordovician – Late Permian
Monobathrida is an extinct order of stationary upper-level epifaunal suspension feeders
Characteristics of the Order
- Monocyclic calyx
- Hexagonal or pentagonal bases
- Dorsal cup has one circlet of plates below the raials
Treatise on Invertebrate Paleontology, Part T, Vol. 2(2) (1978):
- Calyx monocyclic
Sperng and Parks, (1953):
- PENTAGONAL BASES-The development of the various types of bases in pentagonal based Monobathrida seems to have proceeded through the anchylosis of sutures to produce crinoids having unequally quadripartite and tripartite bases
- HEXAGONAL BASES-There are, within the hexagonal-based Monobathrida, four normal arrangements of basal plates. These are shown in figures la, b, c, and d. The derivation of the quadripartite (fig. lb) from the pentapartite (fig. la) requires only a simple anchylosis of the anterior suture (fig. 8). The derivation of the equally tripartite base (fig. Ic) is a more difficult problem. Wachsmuth and Springer derived this type of base from an unequally tripartite, pentagonal base by the addition of an x element to the left anterior basal (figs. 3b and c). Wilson derived this type of base in two ways: (a) from a quadripartite, pentagonal base (figs. 4d and e); and (2) from a pentapartite, pentagonal base (figs. 4f and g). In both cases, he suggests a combination of plate atrophy and compensating hypertrophy as factors which would achieve such a result.
- For figures, see Sperng and Parks (1953), page 590
- The dorsal cup of Monobathrida has only one circlet of plates below the radials. The order contains two suborders named Tanaocrinina and Glyptocrinina, both ranging from Ordovician to Permian but having somewhat different abundance from system to system.
Moore and Laudon (1943)
- Monocyclic camerate; major families divided due to variations within cup structure; cup nanaocrinoid stock or glyptocrinoid stock. Tanaocrinoid stock may have four or five plates in the basal circle of the dorsal cup; many have tripartite base with hexagonal outline; three plates of equal size. Glyptocrinoid stock with prominent stellate plates, distinct median ray ridges, depressed interbrachial areas; anal X displaced upward to position above radials, allowing lateral contact of plates all around circlet; anal X displacement defining characteristic of Glyptocrinoid stock.