The sea-urchins, ophiuroids and crinoids also have yielded many important novelties to A.
The Tornaria larva offers a certain similarity to larvae of Echinoderms (sea-urchins, star-fishes, and sea-cucumbers), and when first discovered was so described.
Klein (1734) to denote the tests of the Echini or sea-urchins; its later use for the animals themselves, or for the whole phylum, was an error in both history and etymology.
Those plates are perhaps constant throughout sea-urchins and starfish (though it would puzzle any one to detect them in certain Silurian echinoids), and they may be traced in some of the fixed echinoderms; but there is no proof that they represent the radials of a simple crinoid, and there are certainly many cystids in which no such plates existed.
They do not feed on fish, like true otters, but on clams, mussels, sea-urchins and crabs; and the female brings forth but a single young one at a time, apparently at any season of the year.
North of the Atlas it belongs to the European type, in the south it contains a fauna of oysters and sea-urchins belonging to the facies " africano-syrian " of Zittel.
There was also sufficient comprehension of the differences between the main classes of Echinoderms - the sea-urchins or Echinoidea, the starfish or Asteroidea, the brittle-stars and their allies known as Ophiuroidea, the worm-like Holothurians, the feather-stars and sea-lilies called Crinoidea, with their extinct relatives the sac-like Cystidea, the bud-formed Blastoidea, and the flattened Edrioasteroideawhile within the larger of these classes, such as Echinoidea and Crinoidea, fair working classifications had been established.
12, B); but the sea-urchins present a more difficult problem, on which Bothriocidaris sheds no light.
Lime is, in fact, absorbed to an enormous extent by fishes, molluscs, crustacea, calcareous algae and sponges, starfishes, sea-urchins and feather stars, many polyzoa and a multitude of protozoa (mainly the foraminifera).
Corals, both reef-builders and others, flourished in the clearer waters; rugose forms are represented by Amplexoid, Zaphrentid and Cyathophyllid types, and by Lithostrotion and Phillipsastraea; common tabulate forms are Chaetetes, Chladochonus, Michelinia, &c. 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.