How does fragmentation allow some sea stars and brittle stars to reproduce asexually?

Asexual reproduction in some sea stars and brittle stars occurs through fragmentation, a process where the animal's body divides into two or more parts, followed by the regeneration of the missing sections.1

For this process to be successful, the animal must possess a body wall capable of tearing and the ability to seal the resulting wounds. In certain sea stars, fragmentation is triggered when two groups of arms pull in opposite directions, effectively tearing the animal into separate pieces.1

Crucially, successful regeneration depends on the presence of specific body parts in the fragmented pieces. For many sea stars and brittle stars, a new individual can only be generated if a portion of the central disk remains attached to the detached arm or body segment. Once these conditions are met, the organism regrows the lost parts to form a complete, independent animal. In some species, this method is so effective that sexual reproduction has not been observed.1