Wound healing and regeneration following amputation of arm-tips of the sea star, Leptasterias hexactis, are described using light microscopy, SEM, TEM, and [H] thymidine autoradiography. The process can be divided into a number of stages. Initially, the wound is closed by contractions of the stump-tip. Re-epithelialization then occurs through migration of epidermal cells from adjacent areas over the wound to form a thin wound epidermis. This is converted into a thicker, permanent covering in concurrence with the onset of cell cycle activity in the wound epidermis and adjacent epidermal regions. Histolysis and phagocytosis of damaged tissues occur beneath the new epidermis and a small connective tissue scar develops at the wound site within which muscle differentiates. At this time, elevated levels of [H]thymidine incorporation are initiated in the sub-epidermal tissues of the arm-tip. A variety of differentiated cell types enter the cell cycle including cells of the parietal peritoneum, lining of the radial water canal, and the dermis. Cell division is accompanied by the development of a small new arm-tip complete with terminal ossicle, terminal tentacle, and optic cushion. The radial water canal, radial nerve, and perivisceral coelom extend by outgrowth into this newly developing tip. Accelerated growth of the regenerate then occurs in a zone just proximal to the new tip. There is no evidence of a blastema-like mass of rapidly dividing undifferentiated cells at the tip of regenerating arms. Arm-tip regeneration in this sea star may therefore be best described as a morphallactic-like process in which a true blastema is not formed, but in which scattered cell proliferation plays an essential role.
Maturation in the onychoteuthid squid Moroteuthis ingens was found to be irreversible, with death following shortly after sexual maturation and spawning. Both males and females were found with spent gonads. The ovary reaches very large sizes in mature females and probably prevents feeding by constricting the caecum. There was also a marked difference in the tissue integrity between immature females and females which had reached sexual maturity. Mature and spent females showed advanced tissue breakdown with individuals having a thin mantle wall with an inelastic, gelatinous appearance. Histological examination of the mantle wall revealed that the tissue breakdown was due to a drastic histolysis of muscle tissue and, to a lesser extent, collagen fibres. Mature males also showed some tissue breakdown and loss of muscle fibres but this was not as dramatic as in the females. These features are considered in relation to processes contributing to terminal maturation in M. ingens.
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.
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