Filogenia y especiación en Chaetognatha.

BOLTOVSKOY DEMETRIO

PHYSIS - A

ASOCIACIÓN ARGENTINA DE CIENCIAS NATURALES

Lugar: Buenos Aires; Año: 1978 vol. 38 p. 13 - 25

0325-0342

Besides the factors affecting the speciation process in most marine planktonic taxa, and which also involve Chaetognatha, there seem to be some others' that influence this group in a special way. Some of the latter are concluded to be related to the animal's motility, their cosmopolitism, competition, and origin and evolutive speed of Chaetognatha species. However, the relatively low degree of speciation of the phylum can not be explained on the basis of these' mechanisms alone. It is proposed that although the origin of the phylum itself is remote, the origin of the genus Sagitta (which includes 75 % of the species of the whole phylum) is relatively recent. Some evidences supporting this hypothesis are discussed. Eukrohnia is the oldest chaetognath genus and from it all the other genera originated; the mechanisms that ruled these processes are outlined. Finally it is concluded that with the formation of Sagitta the phylum was "rejuvenated" and the species-formation processes known to have occurred in the last few thousand years are only the beginning of an active diversification presently at work.