In phycology, conceptacles are specialised cavities of seaweeds that contain the reproductive organs. They are situated in the receptacles and open by a small ostiole. The term is used in reference to the Corallinaceae, however they are rarely referred to in any other alga except the Fucales in which they are one of the major characteristics. In the Fucales there is no haploid phase in the reproductive cycle and therefore no alternation of generations. The thallus is a sporophyte. The diploid plants produce male (antheridia) and female (oogonia) gametangia by meiosis. The gametes are released into the sea, after fusion the zygote settles and begins growth.
There are other similar structures: cryptostomata are similar to conceptacles but differ having only hairs and are sterile. Caecostomata, are found only in Fucus distichus, in these the ostiole becomes blocked during development.