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Paul, 1968a

Macrocystella Gallaway, the earliest glyptocystitid cystoid

Paul, C. R. C.
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Macrocystella mariae Callaway 1877, type species of Macrocystella, has a stem which is divisible into proximal and distal portions; a theca composed of 4 basal, 5 infra-lateral, 5 lateral, 6 radial, and some oral plates; a large periproct surrounded by 5 thecal plates; biserial unbranched brachioles grouped into 5 ambulacra and arising from the margins of the flattened oral surface. In all these respects it agrees with Mimocystites bohemicus Barrande 1887, type species of Mimocystites which becomes a subjective junior synonym of Macrocystella. Macrocystella azaisi (Thoral) has 7 orals and thus Macrocystella differs from the rhombiferan Cheirocrinus Eichwald only in the absence of pectinirhombs. The Macrocystellidae are therefore transferred to the rhombiferan superfamily Glyptocystitida. Macrocystella evolved into Cheirocrinus by the acquisition of pectinirhombs. In Macrocystella respiration probably took place through all the thecal plates which are very thin. In Cheirocrinus respiration was restricted to the pectinirhombs thus allowing much thicker and stronger thecal plates to develop. Macrocystella led a freely vagrant existence and may have had internal buoyancy devices. The stem did not provide permanent fixture and may have been used as a organ of locomotion in conjunction with the brachioles.

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