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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.
Adult sea urchins are usually well protected against most predators by their strong and sharp spines, which can be venomous in some species. [32] The small urchin clingfish lives among the spines of urchins such as Diadema ; juveniles feed on the pedicellariae and sphaeridia, adult males choose the tube feet and adult females move away to feed ...
Upload file; Search. Search. ... Download as PDF; ... The subclass Euechinoidea includes almost all living species of sea urchin, with fossil forms going back as ...
Sea urchin tests showing the ball parts of the ball and socket joints that articulate with the spines Iconaster longimanus, the icon seastar, showing plate ossicles Ossicles have a variety of forms including flat plates, spines, rods and crosses, and specialised compound structures including pedicellariae and paxillae .
Close-up of Asthenosoma varium, showing distinctive spines. Asthenosoma varium is a large sea urchin, hemispherical in shape, and growing to a diameter of 25 cm (10 in). ). The plates from which the test is formed are not joined rigidly together, as is the case in most sea urchin
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 ...
These sea urchins have a disc-like body, more or less bulging, structured by a flexible test, which is nearly unique among sea urchins. Most species can grow quite big and live in deep seas, though some genera contain shallow species (especially Asthenosoma). [1] The test is composed of thin and weakly calcified plates, not always continuous.
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.