Lower Ordovician-Upper Devonian
Glyptocystitida is an extinct order of stationary intermediate-level epifaunal suspension feeders
Characteristics of the Order
- Well developed stem
- Divisible into a proximal and a distal portion
- Alteration of inner and outer columnals with spiraling pivot points
Sumrall (2002) (in reference to Sumrall, 1996):
- The alteration of inner and outer columnals with spiraling pivot points is synapomorphous for Glyptocystitida.
- In the rhombiferan superfamily Glyptocystitida (Tremadoc-Upper Devonian) two opposite trends affect the periproct. On the one hand it enlarges significantly in the line Macrocystellidae – Cheriocrinidae – Pleurocystitidae, but it decreases in size in the lines Cheirocrinidae – Glyptocystitidae and Cheirocrinidae – Callocystitidae (Paul, 1972b, p. 25). In the Pleurocystitidae, which would seem to be less well protected than their ancestors, the enlarged periproct was normally held closely against the substrate and may well have been adequately protected by the strongly plated dorsal surface of the theca.
- Ambulacra long, extending down over theca, brachioles numerous
Kesling and Paul; Paul (1968; 1972b):
- Respiratory pore-structures weakened the theca and the evolution of the theca in the crinoid family Porocrinidae (Ordovician) and the rhombiferan superfamily Glyptocystitida may be interpreted as a compromise between the requirements of respiration and protection. Epispires weakened plate sutures as do some early pectinirhombs and fissiculate blastoid hydrosphires. Accessory ridges often develop adjacent to conjunct pectinirhombs and counteract their weakening effects. The spines of echinoids protect the delicate uncalcified tube-feet, which are thus much better protected than the similar diplopores of Paleozoic diploporites. This protection may partly explain the success, in terms of survival and diversity, of respiratory tube-feet in living echinoids compared with the extinct diploporites.