Acera, or the Witches' Dance
ACERA, or the Witches’ Dance (original)
In mud flats along the coast of Brittany we watch acera, small ball-shaped mollusks that are about two inches in diameter. They rest in mud; then, in water, they dance, their skirt-like hood spreading like a dervish's cassock. They spin and spin. The film adds musical accompaniment. We watch them mate and secrete eggs: acera are both male and female, and can form chains with other acera in which they simultaneously mate as a male and as a female. The eggs hatch, and the cycle begins again.
Starring
Watch "Acera, or the Witches' Dance" on Criterion Channel released in 1972. It's a documentary movie, and has a rating of 6.6 out of 10 from Imdb which is usually fine for this kind of movie.