Talk:Arachne/@comment-216.67.70.141-20160808131947/@comment-26814876-20160809000516

Yes, Mermaids, like most bony fish, have swim bladders to help control buoyancy, as we found out in chapter 37.

Also, I'm acknowledging the fact that it's possible that for some species one half may be, as you put it, a "display piece". In one of my internet games (Dawn of the Dragons), Centaurs are said to be only muscle in their human half with all their vital organs in their horse half, so I wouldn't be surprised if it's something along those lines here too.