Hi

SCA- Scheduled Caste Arunthathiyar is a special category in Tamil nadu.

Scheduled Caste Arunthathiyar (SCA) – 16% of 18% reservation is provided, while for whole SC category it is 18 percent.

For SC/SCA, community certificate should be obtained from Tahsildar of Native Taluk of the applicant.

Don't worry if you did not see that on form, you can still fill SC category for a safer side because, SCA is a sub part of SC category only.

Best of luck