It wasn't a clam, but when I first started out we had a major snow storm that caused a 5 day power outage at my house. I didn't have a generator and by the time I knew I would need one a day in to the outage, we couldn't find one. All I could do was slowly watch as my water temp dropped over a period of days to the lower 50s. Until it dropped below 60 my fish and corals were all still alive. In the 50s I lost fish first then some corals. Some corals died and some lived but this was about 15 years ago so I don't really remember what corals they were. Everything slowed down as the temp dropped and nothing died until day 4 or 5. The clam may survive. I would contact live aquaria and let them know your concern so it's on record if thenclam does perish.