Sea urchin
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Sea urchins or urchins are the class Echinoidea within the echinoderms. Approximately 950 species live on the seabed, inhabiting all oceans and depths from the intertidal zone to the deep sea. They ty
Tripneustes ventricosus and Echinometra viridis
Paracentrotus lividus, a regular sea urchin (Euechinoidea, infraclass Carinacea)
A sand dollar, an irregular sea urchin (Irregularia)
Phyllacanthus imperialis, a cidaroid sea urchin (Cidaroidea)
Crinoid
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Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked fo
Sea urchin
…their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals such as crinoids and sponges. Their predators include sharks, sea otters, starfish, wolf eels, triggerfish, and humans. When unchecked by predators, urchins can create…
Crinoid on the reef of Batu Moncho Island
Stalked crinoid drawn by Ernst Haeckel
Stem, theca and arms of a "true" (stalked) crinoid (family Isselicrinidae)
Oxycomanthus bennetti (comatulid)