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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 .
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.
Cidaris cidaris has a small central test from which project a number of long, blunt, widely separated primary spines and a dense covering of short secondary spines. The primaries are pale grey, tipped with green and the secondaries are pale green. The test has a diameter of 7 cm (2.8 in) to 8 cm (3.1 in) and the spines are twice as long as this ...
The subclass Euechinoidea includes almost all living species of sea urchin, with fossil forms going back as far as the Triassic. [1] [2] Taxonomy
The sea potato is a heart-shaped urchin clothed in a dense mat of furrowed yellowish spines which grow from tubercles and mostly point backwards. The upper surface is flattened and there is an indentation near the front. This urchin is a fawn colour but the tests that are found on the strandline have often lost
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 ...
Diadema paucispinum is a small sea urchin with very long, moveable spines which are slender and sharply pointed. They can be up to 25 cm (10 in) long and about four times the diameter of the test. The primary spines are bluish-black in colour, often with pale bands in younger individuals.
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 ...