Rate of arm regeneration and potential causes of arm loss in the feather star Florometra serratissima (Echinodermata: Crinoidea)

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Abstract
Rate of arm regeneration was measured in caged specimens of the stalkless crinoid Florometra serratissima (A. H. Clark) with one, two, three, and five amputated arms. A single arm amputated at the base regenerates to a fully functional condition in under 9 months. Contrary to earlier speculation, the rate of regeneration per arm decreases slightly as the number of regenerating arms on an individual increases. However, the total rate of regeneration of new arm tissue on an individual increases with increasing number of regenerating arms. An arm amputated midway regenerates at a rate similar to that of an arm amputated near the base. In the population of F. serratissima under study, just under 80% of the individuals had at least one regenerating arm. The potential causes of arm loss are considered and some observations are presented which suggest that the sea star Pycnopodia helianthoides and the crab Oregonia gracilis will attack this feather star and cause it to autotomize arms.