Reproductive system of planarians

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Two individuals of Obama ladislavii right after mating. The white structure seen in the upper animal is the protruded penis papilla. Penis papilla of Obama ladislavii.jpg
Two individuals of Obama ladislavii right after mating. The white structure seen in the upper animal is the protruded penis papilla.

The reproductive system of planarians is broadly similar among different families, although the associated structures can vary in complexity.

Contents

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.

Male part of the reproductive system

Scheme of the reproductive system of a freshwater planarian Planarian reproductive system.png
Scheme of the reproductive system of a freshwater planarian
Simplified version of a planarian's reproductive system. Reproductive system of land planarian.png
Simplified version of a planarian's reproductive system.
6 different types of penis found in land planarians: (1) permanent penis papilla, protrusible penis; (2) apparent penis papilla; (3) intra-antral penis papilla; (4) inverted penis; (5) absent penis papilla with ejaculatory duct; (6) absent penis papilla without ejaculatory duct. Land planarian penis types.png
6 different types of penis found in land planarians: (1) permanent penis papilla, protrusible penis; (2) apparent penis papilla; (3) intra-antral penis papilla; (4) inverted penis; (5) absent penis papilla with ejaculatory duct; (6) absent penis papilla without ejaculatory duct.

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. [1]

In land planarians, the structure of the male atrium may be quite variable between different genera. The most common constructions are: [2] [3] [4]

Female part of the reproductive system

The female part of the reproductive system in planarians is formed by two ovaries in the anterior region. Exiting the ovaries, a pair of oviducts (or, more precisely, ovovitelloducts) runs posteriorly towards the gonopore. A group of yolk glands also connects to these ducts, as planarians are neoophorans and thus yolk is not located inside the eggs.

Close to the gonopore, the ovovitelloducts reach a cavity called “female atrium”, which is located posteriorly to the gonopore. The ovovitelloducts may or not meet and become a single duct (common ovovitelloduct) before entering the female atrium. The distal part of the ovovitelloducts is usually sorrrounded by shell glands, which secrete the material that forms the shell of the eggcase (also called cocoon). [5]

Accessory structures

Reproductive system of Girardia tigrina. The large pouch-like structure on the left is the bursa copulatrix. Girardia tigrina cop.jpg
Reproductive system of Girardia tigrina. The large pouch-like structure on the left is the bursa copulatrix.

Among the accessory structures of the reproductive system of planarians, one usually found in freshwater and marine species is the bursa copulatrix, which has the function to store sperm after mating. [6] Some planarians (such as the genera Planaria , Artioposthia , Arthurdendyus , Coleocephalus and Newzealandia ) have a series of finger-like projections, called adenodactyls, near the male and female atria. Adenodactyls contain glands and produce several secretions believed to be useful during reproduction. [7]

Related Research Articles

<span class="mw-page-title-main">Geoplaninae</span> Subfamily of flatworms

Geoplaninae is a subfamily of land planarians endemic to the Neotropical region. Members of this family are sometimes referred to as the Neotropical land planarians. However, one species, Obama nungara has been introduced in Europe.

<i>Luteostriata</i> Genus of flatworms

Luteostriata is a genus of land planarians from Brazil characterized by a yellow body with dark longitudinal stripes.

<i>Obama</i> (flatworm) Genus of worms

Obama is a genus of land planarians from South America. It contains several species adapted to human-disturbed environments, including the only invasive land planarian native to the Neotropical realm, Obama nungara, which has been accidentally introduced in Europe.

<i>Cratera</i> (flatworm) Genus of flatworms

Cratera is a genus of land planarians found in South America.

<i>Notogynaphallia</i> Genus of flatworms

Notogynaphallia is a genus of land planarians from South America.

<i>Issoca</i> Genus of flatworms

Issoca is a genus of land planarians from Brazil.

<i>Amaga</i> (flatworm) Genus of flatworms

Amaga is a genus of land planarians from South America.

<i>Bogga</i> Genus of flatworms

Bogga is a genus of land planarians from South America. It is monotypic, being represented by the single species, Bogga bogotensis, which occurs in Bogotá, Colombia.

Gigantea is a genus of land planarians from the Neotropical realm.

Timyma is a genus of land planarians from Chile. It is the sole genus of the subfamily Timyminae.

Gigantea maupoi is a species of land planarian belonging to the subfamily Geoplaninae. It is known from specimens collected near Medellín, Colombia.

Gigantea urubambensis is a species of land planarian belonging to the subfamily Geoplaninae. It is known from specimens collected in rainforests of the Lower Urubamba River valley in Peru.

Choeradoplana banga is a species of land planarian belonging to the subfamily Geoplaninae. It is found in areas within the Atlantic Forest in Brazil, such as Cantareira State Park.

<i>Choeradoplana benyai</i> Species of flatworm

Choeradoplana benyai is a species of land planarian belonging to the subfamily Geoplaninae. It is found in areas of Atlantic Forest within Rio Grande do Sul, Brazil, such as São Francisco de Paula.

<i>Choeradoplana minima</i> Species of flatworm

Choeradoplana minima is a species of land planarian belonging to the subfamily Geoplaninae. It is found in areas of Atlantic Forest within Rio Grande do Sul, Brazil, such as São Francisco de Paula.

Choeradoplana pucupucu is a species of land planarian belonging to the subfamily Geoplaninae. It is found in areas within the Atlantic Forest in Brazil, such as Serra da Bocaina National Park and in municipalities such as Teresópolis, São José do Barreiro, Salesópolis, and Ribeirão Pires.

Cratera hina is a species of land planarian belonging to the subfamily Geoplaninae. It is known from specimens found in the Paranapiacaba Conservation Units Mosaic in Brazil.

Cratera arucuia is a species of land planarian belonging to the subfamily Geoplaninae. It is known from specimens found in Intervales State Park in Brazil.

Cratera boja is a species of land planarian belonging to the subfamily Geoplaninae. It is known from specimens found in Serra da Bocaina National Park in Brazil.

Geoplana iporanga is a species of land planarian belonging to the subfamily Geoplaninae. It is found in areas of the Atlantic Forest within Intervales State Park in Brazil.

References

  1. Ogren, R. E. and Kawakatsu, M. (1990). Index to the species of the family Geoplanidae (Turbellaria, Tricladida, Terricola) Part I: Geoplaninae. Bulletin of Fujis Women's College. 29: 79-166.
  2. Carbayo, Fernando; Álvarez-Presas, Marta; Olivares, Cláudia T.; Marques, Fernando P. L.; Froehlich, Eudóxia M.; Riutort, Marta (2013). "Molecular phylogeny of Geoplaninae (Platyhelminthes) challenges current classification: proposal of taxonomic actions". Zoologica Scripta. 42 (5): 508–528. doi:10.1111/zsc.12019. ISSN   0300-3256.
  3. Grau, José Horacio; Sluys, Ronald; Froehlich, Eudóxia Maria; Carbayo, Fernando (2012). "Reflections on the genus Amaga Ogren and Kawakatsu 1990, and description of a new genus of land planarian (Platyhelminthes: Tricladida: Geoplanidae)". Journal of Natural History. 46 (25–26): 1529–1546. doi:10.1080/00222933.2012.691996. ISSN   0022-2933.
  4. Lemos, V. S.; Cauduro, G. P.; Valiati, V. H.; Leal-Zanchet, A. M. (2014). "Phylogenetic relationships within the flatworm genus Choeradoplana Graff (Platyhelminthes : Tricladida) inferred from molecular data with the description of two new sympatric species from Araucaria moist forests" (PDF). Invertebrate Systematics. 28 (6): 605. doi:10.1071/IS14003. ISSN   1445-5226.
  5. Sluys, R.; Kawakatsu, M.; Winsor, L. (1998). "The genus Dugesia in Australia, with its phylogenetic analysis and historical biogeography (Platyhelminthes, Tricladida, Dugesiidae)". Zoologica Scripta. 27 (4): 273. doi:10.1111/j.1463-6409.1998.tb00461.x.
  6. Kaburaki, T. (1922). One some Japanese Tricladida Maricola, with a Note on the Classification of the Group. Journal of the College of Science, Tokyo Imperial University. 54: 1-54.
  7. Graff, L. v. (1896). Über die Morphologie des Geschlechtesapparates der Landplanarien. Verhandlungen der Deutschen Zoologische Gesellschaft: 75-93.