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Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (/ ˌ æ s t ə ˈ r ɔɪ d i ə /). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish are also known as asteroids due to being in the class
Labidiaster annulatus has a wide central disc and 40 to 45 long narrow rays and can reach a diameter of 60 centimetres (24 in). [2] The disc is slightly inflated and is raised above the base of the rays. The madreporite is large and near the edge of the disc. The aboral or upper surface is covered in a meshed network of small slightly ...
The gonads at least periodically occupy much of the body cavities of sea urchins [47] and sea cucumbers, while the less voluminous crinoids, brittle stars and starfish have two gonads in each arm. While the ancestors of modern echinoderms are believed to have had one genital aperture, many organisms have multiple gonopores through which eggs or ...
Underside of a sunflower sea star. Sunflower sea stars can reach an arm span of 1 m (3.3 ft). They are the heaviest known sea star, weighing about 5 kg. [4] They are the second-biggest sea star in the world, second only to the little known deep water Midgardia xandaros, whose arm span is 134 cm (53 in) and whose body is 2.6 cm (roughly 1 inch) wide. [7]
The genus Linckia, as is true of other species of starfish, is recognized by scientists as being possessed of remarkable regenerative capabilities, and endowed with powers of defensive autotomy against predators: [citation needed] Although not yet documented, L. laevigata may be able to reproduce asexually, as does the related species Linckia ...
For decades, scientists theorized a starfish didn’t have heads. A new study finds that they might, in fact, only have heads.
Marthasterias glacialis is a fairly large starfish with a small central disc and five slender, tapering arms. Each arm has three longitudinal rows of conical, whitish spines, usually with purple tips, each surrounded by a wreath of pedicellariae. The background colour is variable and may be brownish or greenish-grey, tinged with yellow or red ...
When L. clathrata loses part or all of an arm through predation, it can regenerate the limb.The damaged area is sealed off, and a new small arm-tip appears within a week. Subsequent development is at the rate of about 3.7 mm (0.15 in) a month, although this slows down when regeneration is nearly complete.