page_title: Theodoxus fluviatilis
section_title: Reproductive system
hierarchical_section_title: Theodoxus fluviatilis / Description / Reproductive system
caption_attribution_description: English: Drawing of the reproductive system of a male of Theodoxus fluviatilis shows testis, prostate, vas deferens and penis.
context_page_description: Theodoxus fluviatilis, common name the river nerite, is a species of small freshwater and brackish water snail with a gill and an operculum, an aquatic gastropod mollusk in the family Neritidae, the nerites.
  This widely distributed neritid snail species occurs from Europe to Central Asia. It has a thick shell with a calcified operculum. The coloration pattern on the shell is very variable. Theodoxus fluviatilis lives in freshwater and in brackish water, in rivers and lakes on stones. It feeds mainly by grazing on biofilms and diatoms.
  Some of the populations of this species are spreading, and these can reach densities up to thousands of snails per square meter. Females lay egg capsules, each of which contains a large number of eggs, but only one snail hatches from the capsule. The snails reach sexual maturity in a year, and the total lifespan is 2 or 3 years.
context_section_description: Theodoxus fluviatilis has separate sexes (i.e. these snails are dioecious). The diploid number of chromosomes (2n) is 25 in males and 26 in females. There is X0 sex-determination system in Neritidae, and it was confirmed for this species too.
  Females have two openings located under the edge of the mantle in the mantle cavity: the opening of the vagina and an opening for laying eggs. The vagina accepts the sperm during copulation. The vagina is connected to the bursa copulatrix and to the spermatheca (for storing sperm). The other opening is for laying eggs. Egg cells originate in the ovary. Egg cells travel through the oviduct to the fertilization chamber, where fertilization occur. Eggs then develop in the glandular uterus. A capsule is formed in the diverticulum next to the uterus. The eggs are then laid.
  In males, the semen is forming in the testis. The sperm structure of Theodoxus fluviatilis was examined by Gustaf Retzius. Then semen travels through the prostate, where it mixes with prostatic fluid. Finally it goes through the vas deferens to the penis. The penis is located on the inner side of the right tentacle.
  The following illustrations show the reproductive system in the female and in the male:
caption: A drawing of the male reproductive system of T. fluviatilis by Lehmann (1873),[54] shows testis (on the left), prostate, vas deferens and penis (on the right).
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