Sexual Reproduction

Breeding season is different among species.

Brooding organ:
1) Any brooding organs are not made in some species, so embryos grow in the peribranchial cavity.
2) Bowl-like brooding organs are made from the branchial sac in some species.
3) Cup-like brooding organs are made from the atrial (peribranchial) wall in Botryllus schlosseri.
4) Sac-like brooding organs are made from the atrial (peribranchial) wall in some species.