PlanetCatfish.com

These were sold to me as O. arnoldi. I got the last five and as soon as I introduced them to the aquarium they started schooling and eating algae. I got them from Petsmart, and I don't really trust their I.D.'s when it comes to fish that have several similar looking species within the genus.

And here's a couple more pics.

Probable Otocinclus hoppei(first and last picture) but it's difficult to say,i hope Mike Noren can id the oto's

Thanks for the reply. Are you talking about the first pic in the first post and the last pic in the second post?
And just FYI, I got them fattened up so they aren't all skinny like they are in the pics.

There is at least two different species in those photos, but neither the photos nor the fish in them are in any condition which allows a good ID (backlit, fright coloration...). Sorry. New photos showing the fish when acclimated to the tank, and showing the whole side including the tail fin of the fish, would help.

EDIT: Although it's definitely not either old-style or new-style arnoldi (cf Otocinclus flexilis in the cat-elog).

EDIT2: ...and I agree with Glenny that the first and last photo seem to show O. hoppei.

Now that they've settled in a little bit they all look like the one in the last picture except for one of them. This one has no spots on the dorsal area and the line going down its side is unbroken. I couldn't get any pics of the caudal fin but it has the same two verticle stripes on it that the rest of them do.
Edit: Here's a pic of another one that looked a little different. From looking at some pics on the internet, they seem to be pretty variable in color (or commonly misidentified). I'm hoping they're all the same species as I hope to get them to spawn one day. Sorry about the poor quality of photos. I can never get decent pics from this tank.