| Popis: |
In the Australia-New Zealand region there are eleven species in the asteroid genus Patiriella that exhibit varying degrees of direct development. P. regularis, the New Zealand species is dioecious and lies at one end of the range of life histories exhibited by the group in spawning small eggs and developing via typical planktotrophic bipinnaria and brachiolaria larvae. The Australian Patiriella have direct development with the brooding species, P. vivipara exhibiting the most derived life history of the group. Reproduction and development of P. regularis, P. gunni, P. calcar, P. exigua, and P. vivipara are described. P. gunnii and P. calcar are dioecious and develop directly through planktonic yolky brachiolariae. P. exigua is a protandrous hermaphrodite and has benthic development through a highly modified non-feeding brachiolaria. P. vivipara is a simultaneous hermaphrodite, has small ova and gestates its young in the ovaries. This species gives birth to large crawl-away juveniles and development is supported by an extraembryonic source of nutrients. The indirect development of P. regularis, provides a reference with which to compare the embryology of the Australian Patiriella. The processes underlying the shift to direct development in Patiriella are examined and the evolution of direct development in the genus is discussed. |
