Remember Silurian Nautilus, Lingula and other Brachiopods, and Nucula, and amongst Echinoderms, the Silurian Asterias, etc.
"More Letters of Charles Darwin" by Charles Darwin
Nucula, a persistent type.
"More Letters of Charles Darwin Volume II" by Charles Darwin
Genres Pinna, Mytilus, Modiola, Nucula.
"Lamarck, the Founder of Evolution" by Alpheus Spring Packard