Crinoid: Permian Period (280 million years ago) Jimbacrinus bostocki, attractive plate with six crinoid specimens with superb detail, from Western Australia, about 26 x 20 cm. [Jimbacinus had five arms that were lined with fine tentacle-like structures called pinnules; echinoderms with mineralised skeletons entered the fossil record 540 million years ago, and today there are still about 600 living species of crinoid]