ostiolus

An ostiolus is a small opening or pore, particularly one found in certain biological structures. The term is derived from the Latin word "ostium," meaning "door" or "mouth." In mycology, an ostiolus refers to the pore at the apex of a perithecium, a flask-shaped fruiting body produced by many Ascomycete fungi. This opening serves as the exit for the ascospores during their dispersal. The ostiolus is often surrounded by specialized cells that can help regulate spore release, sometimes responding to environmental cues like humidity.

Beyond fungi, the term ostiolus can be applied in other contexts. For example, in some botanical descriptions, it might refer to a small pore or opening within a plant structure. In zoology, it might describe a similar small opening in an animal's anatomy, though this usage is less common. The primary and most widely recognized application of the term ostiolus is within the field of mycology, describing the crucial spore-releasing pore of a perithecium. Its function is vital for the reproductive cycle of many fungal species.