Islahi Perveen
Zoology
March 2021
Review of spioniform polychaetes' reproduction and larval growth. Only eight species of the genus Pygospio and a few polydorids have been recorded to reproduce asexually. It is known that there are minor species of Pseudopolydora (also known as Polydorella) and one species of Polydora that only exhibit paratomy. In Pygospio elegans, architomy is frequently the major method of reproduction, which helps to maintain huge populations. Spioniforms have two types of oogenesis (extraovarian and intraovarian), three types of eggs (thin egg envelopes, thick egg envelopes, smooth or reticulated, and thick egg envelopes, honeycombed), and two types of sperm (ect-aquasperm and introsperm). Specific clades only have certain egg and sperm types. Eggs with thickened egg envelopes seem to be unique to spioniforms, but eggs with thin egg envelopes are present in other polychaete groups. This suggests that spionids have plesiomorphic thin egg envelopes. Spermatophores develop in the male nephridia of the spionid subfamily Spioninae. Spioniforms display a variety of reproductive and larval patterns, such as broadcast spawning, external egg masses, female capsule brooding, and female body brooding. In the Spionidae, poecilogony is unusually prevalent. A phylogenetic analysis shows that reproductive and larval traits, together with a few adult characters, offer a more comprehensive database than only adult morphology for assessing systematic and phylogenetic links. The Spionidae are paraphyletic, according to preliminary parsimony studies, hence the definition of the family and the status of related spioniform polychaetes need to be revised with relation to family level classification.
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© Airo Journals 2021
