Psalm 74:12-17 uses the mythic poetry of creation, common to the ANE. The sea monster of v. 13 has multiple heads, just as does Litan in the Ugaritic texts.
For some good biblical cross-references on the sea-monster, see: Pss 89:10; 93:3; Job 26:12; Isa 27:1; 51:9.
A modern impression of an Akkadian gray stone cylinder seal from Tell Asmar, Iraq, depicting two gods spearing a four-legged, seven-headed Hydra. Frankfort 1955, no. 478. Museum no.: IM15618; feared to be looted. Courtesy of Oriental Institute, University of Chicago.