Well, it looks like the end is indeed nigh. That last Pisaster, for whom I held out unreasonable hope for so long, seems to be on its way out. Today it has lost its last two arms, leaving a central disc attached to a single arm:
As bad as it looks, it could be a lot worse. The other stars that disintegrated to this degree were essentially amorphous piles of goo, and this one is still somewhat intact. It also hasn't gone entirely mushy, so it is somehow maintaining its internal pressure. I'm going to keep it for another day and see how it looks tomorrow.
The other two arms, on the other hand (ha!), were a mess. When I got to the table this afternoon they were both semi-attached and semi-upside down behind one of the quarantine tanks. And they were very mushy; when I picked them up they just collapsed the way sea cucumbers do before they start firming up. Gross.
This has to be the end, if only because I don't have any more Pisaster stars to die. Unless the Patiria and Dermasterias stars that I quarantined start getting sick, the outbreak in my seawater table is over, simply because there are no more victims to be infected. From a pathogen's perspective a 100% mortality rate is a bad thing--if all hosts of a population are killed then the pathogen will die with them. However, my table is connected by water supply to other tables and labs, and I have a sneaking suspicion that the pathogen is out there in Monterey Bay (the source of our seawater), in which case there's nothing I can do about it. Actually, I can do something. I can cross my fingers and hope for the best.