Phoronids may be hermaphrodites or single sexed, and may also reproduce asexually. Gametes are released through the nephridia. Fertilisation is probably internal. Phoronids follow one of two types of reproductive strategy. Some species, such as "Phoronis ovalis", lay only a few (12–25) large eggs which have a lot of yolk. These eggs are brooded within the adult's tube, they are released only when they have hatched. The second strategy is to lay a much larger number (up to 500) of smaller eggs. These eggs are released as soon as they are fertilised. They hatch a few days later into what is called an 'actinotrocha' larvae. The larvae undergo a planktonic development for 2–3 weeks, and settle after about 20 days. Metamorphosis is 'catastrophic', occurring in less than 30 minutes and leading to a slender young phoronid.