Article: A parablastoid from the Arenig of South Wales
Blastoidocrinus antecedens, from the early Arenig Bolahaul Member of the Ogof Hen Formation at Llangynog, South Wales, is the oldest known parablastoid and the first recorded from the British Isles. It is characterized by almost smooth deltoids with weakly scalloped margins and a stellate thecal outline. A single deltoid is known from the Treionverth Formation (Upper Arenig) of Anglesey.Currents in the respiratory cataspires of parablastoids entered the aboral slits and exited through the adambulacral pores, contrary to Hudson's (1915) interpretation. Cataspire canals deepened during growth by internal resorption and external resecretion within the thecal cavity. This wasteful mode of enlargement may have limited the success of the Parablastoidea.