Questions on "dhiSNya"

[Sudalaimuthu Palaniappan]

It looks as if the CT usage "tittiyam", a vedic fire,  might refer to Sanskrit
"dhiSNya" which also has a variant form "dhiSTya" according to Monier
Williams. But the loan phonology has a problem. If the Tamil word was borrowed
directly from the Sanskrit form with retroflex "-ST-", in Tamil we should have
-TT- and not -tt- as we do in "tittiyam". So the source of the Tamil word
could not have had retroflexion. Is "dhiSNya" ever referred to in Pali or
Prakrit as "dhittya" or "dhittiya"? If Pali or Prakrit does not have the form
with dental, could the original form of "dhiSNya" before retroflexion be
"dhisnya" or "dhistya"?

Was this fire used to sacrifice animals such as turtles?

Can the Vedic scholars help? Thanks in advance.

Regards
S. Palaniappan