Very rarely a ray of a sea star is unusually wide and has two parallel ambulacral grooves that extend to a single tip. Such a ray has two terminal plates that are coalesced laterally. This abnormality is inferred to develop as a rare result of regeneration because it is recorded from a species with obligate asexual reproduction (fission and regeneration of halves; no gametes). This conclusion is supported also by an example where the abnormality affects only the distal third of a ray