This MerMay thing (whatever it is XD) gave a good enough excuse to draw examples of the Selkies and Nereids as they appear in the AER-verse  (examples because they vary massively in appearance depending on...a  lot of things).  I attempted a more "stereotypical" mermaid here which  meant it's either an early Nereid or a reef/shallow water Nereid.  The  ones that live in shallow water are more likely to resemble Base  humans.  The ones that live out in the deep sea only bear hints that  they evolved from humans. 

The Selkies usually have the cetacean/seal traits such as horizontal  tails and breathe air.  Nereids have more fish/aquatic animal tendencies  such as gills (which uses the existing nose structures with  modifications for the shallow water ones and gill slits in the deeper  water ones) and vertical tails and an abundance of fins (though this one  only has a fin on the head).

I varied from my usual sketch colouring (which is fill circle for  flats and  soft mix brush for shading and sometimes big texture stamp  brush for background) and used the wet bristle brush for everything.   Will definitely be using it for sketches that don't involve intricate  patterns or tattoos as unlike the mix brush (which should be used on the  same layer but you can get away with using it on a different layer) the  wet bristle brush really needs to be used on the same layer.  And me  and things on the same layer don't always work out so good.