The term "Shaivite" is overused nowadays. For instance, Iyer Brahmins are often called Shaivites, but they're actually followers of Adi Shankaracharya's Smartha sect (which I discuss here and here), and simply adopt Shiva as their Ishta Devata. True philosophical Shaivism is relatively rare nowadays (in contrast to philosophical Vaishnavism which is pretty common). I discussed one genuine Shaivite sect, the Lingayat sect of Basava, in my answer here. But my question is related to a more famous sect of Shaivism, known as Shaiva Siddhanta, which is based on the Shaiva Agamas and the poems of the Nayanars just as the Sri Vaishnava sect (of which I'm a member) is based on the Pancharatra Agamas and the poems of the Alwars.
Now the figure most responsible for combining the Sanskrit and Tamil wings of Shaiva Siddhanta is Aghorasiva, a Shaiva Siddhanta Acharya who lived in the 12th century. In any case, in this excerpt from Aghorasiva's Kriyakramadyotika, Aghorasiva discusses the steps a guru must take before he initiates a new shishya into the Shaiva Agamas. In particular, he has to invoke the Lokapalakas, the guardians of the directions. One of the Lokapalakas is Vishnu, and here is the description of Vishnu's appearance that's supposed to be meditated on:
[E]ndless, covered by tens of thousands of snake hoods, shining like a flash of lightning, mounted on a tortoise, with his hands in the anjali mudra.
Now some of these attributes are recognizable; Vishnu is indeed endless and shining, and he is covered by the countless hoods of the serpent Adiseshan. But my question is, what scriptures describe Vishnu as riding a tortoise?
Vishnu's usual Vahana is his eagle Garuda. The only gods I know of who have a tortoise as a Vahana are Yama, Varuna, and possibly Sadashiva (as I discuss here). But is Vishnu ever described that way as Aghorasiva suggests?
