Complex sentence: Anatomical examination indicates that the pelagic thresher is unlikely to be warm-bodied like the common thresher; it lacks a rete mirabile, a blood vessel countercurrent exchange system that prevents metabolic heat from being dissipated into the water, inside its trunk.
Split into simpler sentences: Anatomical examination indicates that the pelagic thresher is unlikely to be warm-bodied like the common thresher. The pelagic thresher lacks a rete mirabile, a blood vessel countercurrent exchange system that prevents metabolic heat from being dissipated into the water, inside its trunk.