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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 .
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 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 ...
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
It is one of the few sea urchin that can survive many hours out of water. [45] Sea urchins can be found in all climates, from warm seas to polar oceans. [40] The larvae of the polar sea urchin Sterechinus neumayeri have been found to use energy in metabolic processes twenty-five times more efficiently than do most other organisms. [46]
The Diadematidae are a family of sea urchins. Their tests are either rigid or flexible and their spines are long and hollow. [2] Astropyga Gray, 1825 Astropyga radiata (Leske, 1778), extant; Astropyga pulvinata (Lamarck, 1816), extant; Astropyga magnifica (Clark, 1934), extant; Centrostephanus Peters, 1855 Centrostephanus asteriscus (Agassiz ...
Perischoechinoidea is a subclass of primitive sea urchins that were abundant in the Palaeozoic seas. However, the great majority of species died out during the Mesozoic, as the more advanced euechinoid sea urchins became common. Today, only a single order, the Cidaroida, survives.