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Updated: May 6, 2025
Among the Echinoderms we find that the Cystids and Blastoids have gone, and the sea-lilies reach their climax in beauty and organisation, to dwindle and almost disappear in the last part of the Mesozoic. One Jurassic sea-lily was found to have 600,000 distinct ossicles in its petrified frame. The free-moving Echinoderms are now in the ascendant, the sea-urchins being especially abundant.
Their development is obscure, but it must be remembered that the rocks only give the record of shore-life, and only a part of that is as yet opened by geology. Some experts think that they were developed in inland waters. The quaint stalked Echinoderm which also we noticed in the Cambrian shallows has now evolved into a more handsome creature, the sea-lily.
In the others a strong limy skeleton was developed, and the nerves and other organs were modified in adaptation to the bud-like or flower-like structure. In the living Comatula we find a star passing through the stalked stage in its early development, when it looks like a tiny sea-lily. * See the section on Echinoderms, by Professor MacBride, in the "Cambridge Natural History," I.
Some of these Cystids will presently blossom into the wonderful sea-lily population of the next age, some are already quitting their stalks, to become the free-moving star-fish, of which a primitive specimen has been found in the later Cambrian. This slight sketch of the Cambrian population shows us that living things had already reached a high level of development.
In the next geological age the stalk will become a long and flexible arrangement of muscles and plates of chalk, the cup will be more perfectly compacted of chalky plates, and the five arms will taper and branch until they have an almost feathery appearance; and the animal will be considered a "sea-lily" by the early geologist.
The sea-lily fills the rocks no longer; the sea-urchin is very abundant. The Molluscs gain on the more lowly organised Brachiopods. To complete the picture we must add that higher types probably arose in the later Cretaceous which do not appear in the records. This is particularly true of the birds and mammals.
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