Odd sea creatures moving in formation

At first glance the video appears to show some kind of gross leech lurking in a pond. I even thought it resembled a fat version of the SR-71 Blackbird, a 1950s Cold War era jet, able to cruise on the edge of space and outfly a missile.

It's refreshing to see that it is twin manatees following their mother gracefully on either flank. Serenity now.