Stingrays defend themselves with a serrated spine of vasodentine, sheathed in venom-producing tissue and set part way along the tail. Mantas belong to the same order, Myliobatiformes, but the giant oceanic manta carries only a calcified mass near the tail base, without the groove or the serrations that make a stingray barb dangerous.
The trade-off is size and mobility. A disc spanning up to about seven metres, wings that beat rather than ripple, and a life spent ranging across open water leave little use for a bottom-dweller's defence. Feeding shifted in the same direction: the mouth sits at the front of the head, flanked by cephalic lobes that funnel plankton-rich water over rows of filtering gill plates.
What remains argued over is how far manta cognition goes. The species has the largest brain recorded in any fish, and a small 2016 study reported mirror-directed behaviour, but the sample was two animals and the interpretation is still contested.