Early Tamil texts have preserved planetary names which go back to the Dravidian language of the Indus Civilization, for they can be verifiably read in the Indus inscriptions. See
Parpola, Asko, 1994. Deciphering the Indus script, Cambridge University Press, p. 179ff.
Parpola, Asko, 2015. The Roots of Hinduism: The Early Aryans and the Indus Civilization, Oxford University Press, p. 266ff.
For Śani/Saturn in particular, see 1994 p. 197 and 2015 p. 276, and for Saturn’s (and the night-sun’s) connection with the tortoise, p. 206-208.
With best wishes, Asko
Mevissen, Gerd. J.R. 2000, Īṣat-paṅgu Śanaiścara, the Lame Planetary God Saturn and His vāhanas, Serie Orientale Roma, Vol. XC. Roma: 1267-1297.