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Fossil of Acrocidaris, an extinct sea urchin Echinoid fossils are the fossilised remains of sea urchins , spiny marine invertebrates that live on the seabed. Humans have been interested in these fossils for millennia, have considered them lucky, have imbued them with magical powers and linked them to their deities .
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An inverted sea urchin can right itself by progressively attaching and detaching its tube feet and manipulating its spines to roll its body upright. [2] Some species bury themselves in soft sediment using their spines, and Paracentrotus lividus uses its jaws to burrow into soft rocks.
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The Echinothurioida are an order of sea urchins in the class Echinoidea. Echinothurioids are distinguished from other sea urchins by the combination of a flexible test and hollow spines. The membrane around the mouth contains only simple plates, in contrast to the more complex mouth parts of their close relatives, the Diadematoida. They are ...
Tripneustes gratilla, the collector urchin, is a species of sea urchin. Collector urchins are found at depths of 2 to 30 metres (7 to 100 ft) in the waters of the Indo-Pacific, Hawaii, the Red Sea, and The Bahamas. They can reach 10 to 15 centimetres (4 to 6 in) in size.
Echinometra mathaei grows to a test diameter of about 5 centimetres (2.0 in). The colour is quite variable but the test is usually a dark colour. The spines are sometimes green and purple with purple tips or entirely green with purple tips but this sea urchin can be distinguished from other species by a characteristic pale ring at the base of each spine.
The banded sea urchin has a slightly oval test (shell), reaching a diameter of about 5 cm. [1] Like almost all the Diadematidae (but it is in Echinothrix calamaris that it is most obvious) it has two different sets of spines, short and slender closed spines which go from yellow to dark (through brown) in colour and can deliver a nasty sting, and longer and thicker spines that are often banded ...