Crinoids: Sub-Class Inadunata

© Craven & Pendle Geological Society

This sub-class is distinguished from the Camerata by possessing a rigid cup in which the brachials are free (or sometimes loosely connected) above the radials.  The mouth is situated beneath the tegmen which is usually flat or depressed but the food grooves are on the surface of the tegmen and are covered by fixed ambulacral plates.  The arms are both pinnulate and non-pinnulate.

The sub-class had its greatest development in the Lower Palaeozoic and only a single family continued into the Triassic when it also became extinct.  There are two orders:

1CLADOIDEA - dicyclic Inadunata with basals and infrabasals.  It is one of the most important groups of Palaeozoic crinoids.  The earliest representatives are simple but later forms were more complex.  Typical genus types represented in the Clitheroe area are: Bollandocrinus, Cyathocrinites, Poteriocrinites.

2DISPARATA - monocyclic Inadunata without infrabasals.  The cup contains only basals, radials and usually an anal plate and a radianal.  Eg. Synbathocrinus

Another marked difference between the Inadunata and the Camerata is that the arms in the Inadunata were always free above the radials and there are no fixed brachials.  Also the Inadunata are predominantly dicyclic (with infrabasals) whereas the Camerata are dominantly monocyclic (without infrabasals).