The Love Life of an Octopus (1967)
An octopus slithers into a narrow crack near the shore; we see its eye up close. It feeds on a crab. In spring it's time to mate. A male grabs a female; he inserts his third arm in her respiratory cavity. We watch another pair: a larger female is the aggressor here. Mating is repeated over hours and days. The female releases strings of fertilized eggs that hang from the roof of a nest. She guards her spawn for a month, fanning the strings to circulate water for oxygen and cleanliness.
