page_title: Reproductive system of planarians
section_title: Male part of the reproductive system
hierarchical_section_title: Reproductive system of planarians / Male part of the reproductive system
caption_attribution_description: English: Planaria reproductive system diagram.
context_page_description: The reproductive system of planarians is broadly similar among different families, although the associated structures can vary in complexity.
  All planarians are hermaphrodites, so their reproductive system has a male and a female part. Both parts communicate with the surface of the body via a single opening called gonopore, which is located on the ventral side of the posterior half of the body.
context_section_description: The male part of the reproductive system in planarians has a set of several testicles, distributed throughout the body in two or more rows. They are usually concentrated in the anterior two thirds of the body, although they can reach close to the posterior end. The testicles are connected to a pair of sperm ducts which run posteriorly towards the gonopore.
  In some groups, the sperm ducts met in their distal part, forming the ejaculatory duct, which then opens in a cavity called “male atrium”. In others, like land planarians, both open in the prostatic vesicle, a glandular organ which then runs posteriorly and opens in the male atrium, usually through an ejaculatory duct. The male atrium is located anteriorly to the gonopore.
  Usually associated to the ejaculatory duct, there is a structure formed basically by a fold of the walls of the male atrium called “penis papilla”. The penis papilla is a permanent structure that occupies part or the whole male atrium and is protruded during copulation, thus also called a protrusible penis. In species without a penis papilla, the penis is formed only during copulation by a projection of the walls in the male atrium and called an eversible penis.
  In land planarians, the structure of the male atrium may be quite variable between different genera. The most common constructions are:
  Permanent or true penis papilla: A big penis-like fold occupies the whole male atrium or most of it and is crossed by an ejaculatory duct. It is found in the genera Geoplana, Obama, Cratera, Paraba, Polycladus, Microplana, among others.
  Apparent penis papilla: Similar to a true penis papilla, but with a wide ejaculatory cavity instead of an ejaculatory duct. It is found in the genus Matuxia.
  Intra-antral penis papilla: A much smaller version of the true penis papilla, perceived as a small conical structure in the male atrium, which is mostly occupyed by irregular folds. It is found in the genera Amaga and Endeavouria, among others.
  Inverted penis: A structure that fills most of the male atrium, leaving a narrow canal connecting to the prostatic vesicle that resembles an ejaculatory duct. This canal, however, is pushed outwards during copulation, becoming the outer wall of the penis. It is found in the species Choeradoplana minima.
  Absent penis papilla: The male atrium lacks a permanent penis-like structure, i.e., contains an eversible penis, and is usually filled by irregular folds. An ejaculatory duct may be present (as in Pasipha, Imbira and Luteostriata) or not (as in Notogynaphallia).
caption: Scheme of the reproductive system of a freshwater planarian
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