Complex sentence: "Therians" are individuals who believe or feel, on an internal level, that they are non-human animals in a spiritual sense whilst others claim to have a psychological or neuro-biological connection--rather than a spiritual one--to their animal.
Split into simpler sentences: Therians are individuals who believe or feel, on an internal level, that they are non-human animals in a spiritual sense. Others claim to have a psychological or neuro-biological connection--rather than a spiritual one--to their animal.