Seahorse

The following is from "The Current Affairs Field Guide to Socialist Animals" by Lyta Gold and Nick Sirotich:

There are over 50 species of seahorse, all of which display remarkable gender equality. After engaging in an elaborate and respectful series of courtship dances, impregnated males carry the eggs to term. Many individuals are gay, bisexual, or otherwise radically queer. Monogamy is practiced by some individuals, but without the oppressive institution of state-sponsored marriage. With no power hierarchy, seahorses could be said to form the most purely socialist societies on the planet.