Humans love to think we’re the brainiest species around, but leeches have an impressive
32 brains (making them absolute shoo-ins if Mensa ever expands their ranks to include non-human animals). These bloodsucking invertebrates are biologically divided into around 32 separate sections, which each feature their own brain fragment. In addition to housing a leech’s thought centers, these segments serve additional functions: The first few contain a leech’s eyes and front sucker, the middle sections are where you can find the bulk of a leech’s nerves and reproductive system, and the rear portion is home to yet another sucker at its tail end. Some leeches also possess 10 stomachs and nine pairs of testicles (all leeches are hermaphrodites, with both male and female sex organs).
Yet leeches are far from the only living things with more organs than you might expect. Cuttlefish, squid, and octopuses all have three hearts — a systemic heart to pump blood throughout the body, and two branchial hearts used for pumping blood through the gills. Cows famously have a stomach with four separate compartments, but that’s nothing compared to the Baird’s beaked whale, which can have as many as 13 stomachs. Perhaps no animal is more unusual, however, than the Ramisyllis multicaudata, a sea worm with hundreds of butts, each with its own set of eyes and brain.
