Anatomy of finfish and shellfish

Unit 8 - Urino – Genital System

8.4.3. Sharks
The testes are paired and usually placed anteriorly in the body cavity suspended dorsally by means of a “mesorchium”. Often right testis is larger than the left, sperm discharges into a central canal network that communicates with the anterior part of the kidney through efferent ducts tranversing the mesorchium.
The front part of the kidney is modified into a glandular “epididimis” where the archinephric ducts receives the efferent ductles and runs down posteriorly. Just behind the testis the kidney is modified into “Leydig gland” in which the tubules secrete a “seminal fluid” into the archinephric duct.
As the archinephric ducts runs down along the kidney as the vas deferens, it enlarges into a seminal vesicle from which a sperm sac opens dorsally. The vesicles and sperm sacs open into the urinogenital sinus, which in turn empties into the cloaca. From the cloaca sperm enter the grooves of the claspers, through which they can be transferred to the female.
Ovaries are paired, but the left one may be greatly reduced in size in some species. Like the testes, they are placed well anteriorly in the body cavity; each is suspended by a mesovarium. The oviducts open anteriorly to the ovaries and usually have a common mouth or funnel. Eggs are released into the coelom, proceed into this funnel and then traveled down the oviduct to the region of the shellgland (Nidamental gland) where fertilization occurs and a horney shell or membrane as secreted. In oviparous species, the shell is tough and protects the developing embryo. In viviparous species, the shell is slight or vestigial and the young develop in the posterior, uterine portion of the oviducts.