I found this amazing creature in the sea off Jambiani beach, floating on the surface, when I approached and the water swelled around it, it went limp and floppy; almost like the pulsing movement of a jelly fish so presumably a type of self defence.
Fringe like adaptions of the limbs and metallic silver and black; it is an airbreather and smooth skinned (newt like?) I have a couple of videos but thought I would post a photo first to see if anyone can help with identification.
the spiky bits are called papillae/cerata & they're on 3 pairs of "arms" called peduncles (some have 4 pairs).The key difference is that in atlanticus is that on each peduncle the cerata are on a single row (uniseriate) (ie form a flat fan) but in marginatus are multiseriate.
N.B since both species eat Portuguese man-of-war & arm themselves with it's stings they "can be dangerous to humans".