its a MERMAID!!
benign, intensely curious, a gentle giant that starts out its life cycle as a jelly-like egg the size of a watermelon. when they hatch, they resemble marine mammals - fleshy, monochromatic, and very robust. over time they grow and develop longer limbs. they're fast, but not necessarily in accordance with their proportion, sort of how an airplane looks slow as it travels across the sky. once they reach fullsize, they entire their next morphological phase. their skin tightens and hardens into segmented shells, becoming more of a creeping crustacean than a corpulent whale. before the transformation is complete, they breed and the females raise their eggs. a great gossamer red jelly mane looks just like the clutch of eggs (carried on the underbelly) and causes predators to get big gobs of goop instead of a fish egg breakfast.
awful sea legends start because of their curiousity, able to live among the depths or the surface of the sea, they'll tug down boats in "play".
phew. so tired.