Crossword-Solution: BLASTOIDS 9 letters, 1 clue 🏆 scrabble score: 12

The blastoids became more abundant in the Devonian, culminated in the Carboniferous, and disappeared at the end of the Paleozoic.

Amongst the echinoderms crinoids were the most numerous individually, dense submarine thickets of the long-stemmed kinds appear to have flourished in many places where their remains consolidated into thick beds of rock; prominent genera are _Cyathocrinus, Woodocrinus, Actinocrinus_; sea-urchins, _Archaeocidaris, Palaeechinus_, &c., were present; while the curious extinct Blastoids, which included the groups of _Pentremitidae_ and _Codasteridae_, attained their maximum development.

The theory was that all the plates just described, and more particularly those of the cup, which were termed "the calycinal system," could be traced, not merely in all crinoids, but in all Echinoderms, whether fixed forms such as cystids and blastoids, or free forms such as ophiuroids and echinoids, even--with the eye of faith--in holothurians.

Their calcareous skeleton is built upon a plan having five planes of symmetry; this pentamerism is found throughout the crinoids, the blastoids and the free-moving echinoderma.