Where Does 'Snark' Get Its Portmanteau-ishness?

Is a snark

a snake + shark combo
or

a snide + remark combo?

According to yourdictionary.com a snark is -
"An imaginary animal created by Lewis Carroll in his poem 'The Hunting of the Snark'"

According to Urban Dictionary a snark is -

"A combination of "snide" and "remark". Sarcastic comment(s)."

I have to believe that the predominant usage of the word snark in this day and age of blogging refers to the latter.