poi·kil·o·therm 
(poi-kĭlə-thûrm′)
(poi-kĭlə-thûrm′)n.
An organism, such as a fish or reptile, having a body temperature that varies with the temperature of its surroundings.
[Greek poikilos, spotted, various; see peig- in the Appendix of Indo-European roots + -THERM.]
poi′ki·lo·thermi·a (-thûrmē-ə), poiki·lo·ther′my (-thûr′mē) n.
poi′ki·lo·thermic (-mĭk) adj.