Leeches are hermaphrodites meaning that a single individual is both
male and female at the same time. Reproduction occurs through the
production of cocoons that are either attached to a substrate where
they develop or in the family Glossiphoniidae many species of leeches
have the cocoons attached directly to the ventral surface of the
parent (Figure). This allows the parent to protect and care for the
young as they develop. This includes providing food (prey) for the
young leeches after they hatch.
Helobdella papillornata with cocoons visible on
the ventral surface of the parent.
The reproductive systems vary greatly between the different families of leeches. Some families, including the Glossiphoniidae, have a simple pair of gonopores that open to the ventral surface of the leech. Other families, such as the Richardsonianidae, have a complex system with a penis and vagina.
All leeches have paired testisacs that are located within the midbody of the adult leech. The number of testisacs varies depending on the species of leech. The ovisacs of leeches are paired (only one pair) and can be long and tubular, or short and spherical in shape again depending on the family of leech.
Leeches have internal fertilization with most mating by implanting
a "spermatophore" (sperm package) into their partner. This
implantation can by done through the use of a protrusible penis or by
the hypodermic implantation of the spermatophore into the body of the
partner. The sperm are then transported to the eggs where
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