Apex domains cannot have CNAME records.
Question and response
Question
dig 64-127.77.18.185.in-addr.arpa. NS
Answer
64-127.77.18.185.IN-ADDR.ARPA. 5 NS ns2.shellit.org.
64-127.77.18.185.IN-ADDR.ARPA. 5 NS ns3.shellit.org.
64-127.77.18.185.IN-ADDR.ARPA. 5 NS ns1.shellit.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0