Smith, Andrew B. Department of Paleontology, Natural History Museum, London, United Kingdom.
Last reviewed:August 2020
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A small and distinctive order of valvatacean Asteroidea (sea stars) with long, straight-sided arms and relatively small disks. Members of the order Notomyotida (see illustration) have a skeleton that is differentiated into marginals, actinals, and abactinals, and there is a clear calycinal ring. Both supramarginals and inframarginals are present and are offset or alternate rather than vertically aligned as they are in other asteroids. Intermarginal ossicles are not present. On the oral surface, the longest actinal row lies adjacent to the ambulacral groove. Digestive and reproductive organs are confined to the disk and most proximal parts of the arms, and they do not extend well into the arms as in other valvataceans. Dorsal longitudinal muscle bands lie free within the arms and are anchored into the body wall only at their distal and proximal ends.
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