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Most species in this order have five arms and two rows of tube feet with suckers. There are conspicuous marginal plates on the arms and disc. Some species have paxillae and in some, the main pedicellariae are clamp-like and recessed into the skeletal plates. [110] This group includes the cushion stars, [113] the leather star [114] and the sea ...
An echinoderm (/ ɪ ˈ k aɪ n ə ˌ d ɜːr m, ˈ ɛ k ə-/) [2] is any animal of the phylum Echinodermata (/ ɪ ˌ k aɪ n oʊ ˈ d ɜːr m ə t ə /), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". [3]
Brittle stars, serpent stars, or ophiuroids (from Latin ophiurus 'brittle star'; from Ancient Greek ὄφις (óphis) 'serpent' and οὐρά (ourá) 'tail'; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish.
In these, there is a transitory hexamerous symmetry in what is a normally a pentamerously symmetrical genus. The immature individuals with 6 arms appear so different in appearance from mature individuals with 5 arms that they were at one time considered to be two genera, Hydrasterias and Sclerasterias. Juveniles with arms measuring between 8 mm ...
The unusual animals have unique body plans arranged in five equal sections that differ greatly from the symmetric head-to-tail bodies of bilateral animals, which have left and right sides ...
The Asterozoa are a subphylum in the phylum Echinodermata, within the Eleutherozoa.Characteristics include a star-shaped body and radially divergent axes of symmetry. The subphylum includes the classes Asteroidea (the starfish or sea stars), Ophiuroidea (the brittle stars and basket stars), Somasteroidea (early asterozoans from which the other classes most likely evolved), and Stenuroidea ...
Luidia sarsii is a species of starfish.Sand colored with a velvety texture, the species expresses pentamerism or pentaradial symmetry as adults. The five gently tapering arms have conspicuous bands of long white marginal spines in groups of three.
Additionally, female barn swallows, a species where adults have long tail streamers, prefer to mate with males that have the most symmetrical tails. [26] While symmetry is known to be under selection, the evolutionary history of different types of symmetry in animals is an area of extensive debate.