Last year I posted the Osage Creation Myth in which Macrobdella decora is prominent.
Remarkably, leeches appear in a wide variety of creation myths.
In the Qu'ran:
“then of that fluid-drop (nutfa) We created a leech-like clot" (Quran 23:14)
"then did he become a leech-like clot; then did (Allah) make and fashion (him) in due proportion. And of him He made two sexes, male and female.”(Quran 75: 37-39).
In the creation myth of the Bengali Munda people in India, the benevolent Sun god Sing-Bonga is married to the Moon and brings forth a tortoise, a crab and a leech to create the land by bringing up soil from the sea bed. – Dalton (1872: Descriptive ethnology of Bengal, p 197). "SingBonga ordered them to bring a lump of clay (hasa) from the depth of ocean. The tortoise and the crab failed to do it. The leech went deep and deep to the ocean and finally found bit clay from the depths of the ocean and gifted it to the Supreme Sing Bonga. SingBonga by his power transformed the bit of clay into the earth. "
In Shinto creation mythology "After the sun and moon, the next child Izanagi no Mikoto and Izanami no Mikoto gave birth to was the leech-child. When this child had completed his third year, he was nevertheless still unable to stand upright." Alternatively: "The child which was born to them was Hiruko (the leech-child), which when three years old was still unable to stand upright. So they placed the leech-child in a boat of reeds and let it float away."