Answer: humpbackwhale

AnswerCrossword Clue
HUMPBACKWHALEIt arches deeply as it dives
HUMPBACKWHALEDenizen of the deep
HUMPBACKWHALEAquatic singer
HUMPBACKWHALESinger in the sea, literally
HUMPBACKWHALEDiving creature