Valvatida is an order of sea stars within the class Asteroidea. Members of this order occur around the world, from shallow coral reefs to deeper continental-shelf habitats. They are ecologically significant benthic predators, scavengers and grazers and include many species commonly seen by divers and in tide pools.

Characteristics

Valvatid sea stars are typically recognizable by a firm, well-calcified body often framed by conspicuous marginal plates or ossicles. Many species have distinct aboral textures (paxillae, granules or spines), tube feet with suckers for locomotion and feeding, and small pincer-like pedicellariae in some groups. Arm number most often is five, though some taxa show variations. Regeneration of lost arms is common across the order.

Taxonomy and history

The order Valvatida has been refined over time as morphological and molecular studies altered relationships among starfish. Taxonomists divide the order into several families that contain numerous genera and species; for a summary of species and genera counts consult resources on Asteroidea such as the summary at current catalogs. Fossil relatives of sea stars are known from Paleozoic deposits, and molecular evidence continues to improve our picture of how valvatids diversified.

Ecology, examples and human relevance

Valvatids play important roles in benthic communities by controlling populations of invertebrates and by contributing to reef and sediment dynamics. Familiar examples encountered by snorkelers include brightly colored reef stars and arm-bearing species such as members of the genera Asterina, Linckia and Pentaceraster. Some families in the order are notable for their attractive forms and are sought for aquaria and education (family overviews).

Conservation and notable facts

Like other echinoderms, many valvatids are sensitive to temperature shifts, pollution and disease outbreaks; regional declines linked to environmental stressors have highlighted their vulnerability. Because of their ecological roles and sometimes limited distributions, conservation attention to habitat protection and responsible collection is important. Further taxonomic and ecological study continues to reveal the group's diversity and evolutionary relationships (further reading).

  • Distribution: global, shallow to deeper waters.
  • Feeding: predators, scavengers, grazers.
  • Reproduction: sexual spawning and, in some taxa, asexual fragmentation.