I've had six urchins in my DT since I set it up. A seventh has been in my sump, also since set up. Tonight I counted and there are 7 in the DT and you guessed it, none in the sump. These things are several inches across. There's no way he got there through the return pump. The only way possible would be to crawl in to the filter sock and crawl against the flow up the open standpipe. Is that possible?
I can see that happening, I had a sea cucumber go from my refugium to my display before, which involved going from refugium to the sump then through three different chambers in the sump and up the drain line to the display.
