Oogenesis and larval development in Micromaldane spp. (Polychaeta: Capitellida: Maldanidae)

Summary

The morphology of larval development and some aspects of oogenesis are described in Micromaldane spp. from eastern Australia. All four species breed throughout the year, and in all the oocytes are released into the coelom prior to vitellogenesis. Micromaldane androgyne, M. pamelae and M. rubrospermatheca all have solitary oogenesis, while Micromaldane nutricula has “nurse” cells attached to the oocytes throughout vitellogenesis. Mature females of Micromaldane nutricula brood up to two groups of 1–4 directly developing larvae at a time. Newly fertilized eggs are ellipsoidal, 150x350 μm. No ciliation is visible during development. Larvae leave the tube after developing 12 chaetigers. All Micromaldane androgyne adults brood a single batch of two or three directly developing larvae at a time. Newly deposited eggs are 1 mm long and 150 μm in diameter. No ciliation is visible on the larvae during development. Larvae develop 19 chaetigers before leaving the tube. Mature females of Micromaldane pamelae brood single batches of up to 31 larvae at a time. Mature oocytes are ellipsoidal 300 X 150 μm. Larvae show a distinct neurotroch in early stages of development, but this is resorbed as chaetigers are formed. Larvae probably leave the tube at the 16-chaetiger stage.

Comparisons are made with other polychaetes and members of the Capitellida. Micromaldane spp. may be useful in the study of reproductive effort and covariables, outlined for polychaetes by Olive (1985), such as body size with longevity and fecundity (inversely) with brood frequency.

Key words:

• oogenesis
• larvae
• Maldanidae
• Polychaeta