Funny they don't mention the hydra, an amazing little creature, almost(?) immortal:
http://www.wired.com/2015/02/absurd-creature-of-the-week-hyd...
http://www.smithsonianmag.com/science-nature/dont-listen-to-...
Although, since they will eventually die of energy depletion from growing too large, if they actually stopped growing they might go on ... a lot longer?
If humans stopped ageing they'd go on a lot longer, too. But as long as they can't it's a hypothetical scenario in both cases.
http://www.huffingtonpost.com/2012/11/30/lobster-age_n_22159...
So give it a few more years and there should be some firm data on how negligibly senescent they actually are. Much of the present situation was a lack of good data.