I don’t know what you mean by a *right, but a dolphin is in fact superior to a dog in every respect. Any cruelty to a dog would be 1000x more cruel to a dolphin by virtue of the fact that dolphins have self-concept which is comparable to human self-concept. Evidence: dolphins are one of 3 species which recognize themselves in a mirror. In other words, dolphins are cognizant that something is “happening to me,” whereas a dog simply has the reflexive cognition that something is “happening” which is pleasant or unpleasant. Dogs are capable of experiencing pleasure and pain, a dolphin is capable of experiencing tragedy.
A mosquito can feel pain and pleasure, but nobody would argue it has the same “rights” as a dog. In other words, the basic existential “right” to not suffer is not equal among all life, on the contrary it must be mediated by a particular organism’s ability to experience suffering.
On topic, stem cells have zero capacity for experience of anything, let alone such advanced concepts as suffering. Therefore they are not individuals, their scientific study is not “murder,” and any argument to the contrary is most likely religiously motivated delusion based on faith in an arbitrary series of words in an antique textbook.