The oniscid isopod female reproductive system and gestation, with a partial review

Abstract

The oniscid isopod reproductive system consists of two different components: (1) the ovaries containing the oocytes undergoing oogenesis and (2) the marsupium (brood pouch) containing the eggs (after oviposition) and the developing embryos (during embryogenesis). These two components compose the unique reproductive system found in the terrestrial isopods. The reproductive system is described and discussed in several terrestrial oniscid isopod species. Ovarian and oocyte dimension as well as oocyte numbers and diameter are provided, and their seasonal changes are analysed. No significant relationship between ovarian size and oocyte number or dimension could be established. The content of the marsupium changes during the marsupial period when eggs evolved into embryos and later into mancae. There is a certain inter-specific variability in the duration of the marsupium. Do the ova move into the marsupium at different stages of oogenesis, i.e. when only some of them are already mature eggs, whereas other complete oogenesis inside the marsupium? Is there a delayed embryogensis in some of the marsupial eggs resulting in a differential timing in becoming mancae? The subject is reviewed and several new research avenues are pointed out and discussed.