page_title: Echinaster
section_title: Arm regeneration
hierarchical_section_title: Echinaster / Anatomy / Arm regeneration
caption_attribution_description: Français&#160;: L'étoile de mer rouge méditerranéenne Echinaster sepositus, en train de régénérer deux bras perdus, à Banyuls-sur-Mer.
context_page_description: Echinaster is a well-studied and common genus of starfish containing ~30 species and is the second-largest genus found within the family Echinasteridae. The genera Henricia and Echinaster encompass 90% of all the species found within the family Echinasteridae. It contains 30 species, however the number of species in this genus is still debatable because of uncertainty within the genera. This genus is currently sub-divided into two sub-genera: Echinaster and Othilia, evolutionary relationships between the sub-genera is not understood. Echinaster are found in the Pacific, Atlantic and Indian oceans, with most species being studied in the Gulf of Mexico and Brazil. The sub-genera Othilia is thought to encompass species mainly found in the Gulf of Mexico and Brazil. Echinaster is often one of the most studied species within the family Echinasteridae and is often used to find evolutionary relationships.
  Many species found within Echinaster are red, orange, or pink in coloration.
context_section_description: Echinaster can suffer frequent damage to their arms, so it is important they are capable of quick repair. When any part of the arm becomes damaged, the stump of the arm constricts, causing the coelom to seal . The combination of coelomic fluid migrating to the wound site and arm constriction, clots formed and the stump begins to seal, closing any open sites. Papullae appear to deflate and the dense connective tissue becomes more densely packed. Circular muscle fibers contract in the arm causing the tube feet to pull towards the wound. Twenty-four hours into arm regeneration, the body wall of the arm is still contracted and the aboral side of the arm has folded to the oral side. A thin epithelial layer has begun to form and the stump has begun to reform due to dedifferentiated epidermal cells. At this stage, the radial nerve cell has also begun to heal. 72 hours into arm regeneration, the aboral arm wall is still covering the wound site, however, now the body wall has relaxed and the papullae began to inflate again. A new epidermis has formed and is now thicker and stronger than the previous epidermis. Directly beneath the epidermis of the wound, phagocytes can be observed ingesting any bacteria or extra cells which are not necessary for regeneration. Morula cells are also present; these cells focus on wound healing and repairing the extracellular matrix. When the arm is completely repaired, myocytes can be ingested by phagocytes, used a direct source for new cells, or used as a source of energy. Stem cells may also contribute to regeneration in sea stars but little is known about their contributions in the Echinodermata. Altogether, arm regeneration takes a couple of weeks for members of the Echinaster genus, however, the arm begins to repair itself in as few as 3 days.
caption: Echinaster sepositus regeneration
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