Segmental pattern formation following amputation in the flagellum of the second antennae of Asellus aquaticus (Crustacea, Isopoda)

Regeneration of the second antennae of Asellus aquaticus is described here following amputations along the antennal flagellum. The process involves the frequent resorption (loss of the distalmost joint remained on the amputated antenna) and the regular apicalization of the new terminal article. In the distal part of the flagellum, resorption occurs only when less than 70% of the original article length is left. For amputations performed in the proximal meristematic region, where new articles are normally produced, the new terminal article may also divide, sometimes producing articles with abnormal setal pattern; instead, articles that would normally divide may fail to do so if they are the nearest proximal neighbour of the new terminal article. Outcome of the increased production of new articles from the meristematic region is a regenerated antenna with a number of flagellomeres close to that shown by the undamaged controlateral one. Similarities and differences in respect to the processes occurring after amputation in the antennal peduncle, as well as in other arthropod limbs, are discussed. These differences may help with understanding general properties of the regeneration process, such as the distinction between epimorphosis and morphallaxis and the relationship between normal development and regeneration.