Some Sea Stars Can Regrow an Entire Body From One Arm

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Sea stars have an unusual ability to rebuild lost body parts, but a few species take regeneration much further. Some can produce a complete new animal from a detached arm, with documented cases involving fragments around 1 cm long. These detached pieces can gradually rebuild a central disc, mouth, arms and other missing structures, a process that can take many months. This form of asexual reproduction is sometimes called whole-body regeneration. Another unusual example involves the scaly sea star Nepanthia belcheri. Large females can divide by fission, producing two smaller individuals. After the split, the resulting animals develop male-type reproductive organs, and when they grow large enough they can change back into females. The species can therefore combine asexual reproduction by splitting with later sexual reproduction. The ability is not shared equally by every sea star. Many species can regenerate damaged arms, but whole-body regeneration from an isolated arm is much rarer, and the exact requirements differ among species. In some sea stars, a portion of the central disc is needed, while certain species can regenerate an entire body from an arm fragment without the usual central-disc requirement. Regeneration works through a complex rebuilding process. Cells around damaged areas can lose their specialized characteristics and contribute to forming new tissues, after which the missing structures are rebuilt in a coordinated sequence. Scientists continue to study these animals because their regenerative biology offers a useful way to understand how complex tissues and body structures can be rebuilt.