Leech Reproduction

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 on ventral

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 fertilization occurs.

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