REGENERATION AND POTENTIAL FUNCTIONAL-DIFFERENTIATION OF ARMS IN THE BRITTLESTAR, OPHIOCOMA-SCOLOPENDRINA (LAMARCK) (ECHINODERMATA, OPHIUROIDEA)

Arm breakage and regeneration in the brittlestar, Ophiocoma scolopendr ina (Lamarck), were surveyed in southern Taiwan from July 1991 to Apri l 1992. A total or 618 individuals were examined, revealing that in 56 % of individuals, or 19% of arms, were undergoing the process of regen eration. Breakage occurred mainly at the distal 1/3 of the arm. The nu mber of individuals with 3 or more regenerating arms exceeded that of expectation from a binomial distribution, suggesting that individual a rm breakage might be dependent on the status of the other arms. The ar ms, according to their position relative to the madreporite, have diff erent probabilities of being protruded, and they also have different p robabilities of breakage in the field. The arms most frequently protru ded tend to be the most frequently injured. This phenomenon suggests t hat functions of arms may have differentiated despite the similar morp hology of the various arms in the brittlestar. Laboratory experimental results indicate that the rate of regeneration per broken arm average s 0.4 mm/day, whether 1 or 3 arms were injured. Arm position, relative to the madreporite, however, made no difference in regeneration rates when all 5 arms were cut. Nevertheless, when 3 adjacent arms were sev ered, the center arm regenerated faster than the 2 side arms; this did not happen when the 3 injured arms were not all adjacent. The faster regeneration of the center arm may provide the advantage of restoring arm functions sooner.