User blog comment:Gingergreeney/Idea/@comment-3026355-20120131080523/@comment-3146930-20120603231810

All hail the god Anon. But seriously, Percy has spent maybe 2-3 days total at Camp Jupiter and Camp Jupiter has a lot of people, numbering in the hundreds. Just because a character hasn't been mentioned, doesn't mean they don't exist (I mean just look at Jason). Also, Percy most likely hasn't met everyone at camp. Not to mention that not every demigod has made it to camp while others are cast out. Considering children of Neptune are frowned upon, it would be possible that a child of Neptune was simply not allowed to enter the camp.