The attack entry for a tendriculos is the same as for its full attack (one bite and two tendrils). Yeah, OK, so there's precedence for this sort of thing (e.g. hydra), but the tendriculos appears to be an error (one brain, not ten). Error or not?
I consider it an error, since there's nothing in the tendriculos description that says it has a special ability to make more attacks than normal on an attack action.