Things go green in tanks. At Toba Aquarium they have a live Entemnotrochus
rumphii which we sent them about four years ago, having yanked it off its
couch at 200 metres off Amami-Oshima. It continues to thrive in the
laid-back manner of Pleurotomariids, but since arriving in its tank it has
changed colour. The whole shell is now covered with hard, greenish ?algal
growths that resist scrubbing and soon revive. Its water is filtered but it
lives under artificial lighting, and I can't help but suspect this has
something to do with it. At home, it is in almost complete darkness all its
life, and thus probably does not need to protect itself against photophilic
algae.
At Nishinomiya Shell Museum they have a different problem; their three live
Nautilus specimens sport black fur coats like college kids at a ball game
in the 20s. The algae responsible also coated the tank floor, but a few
timely neritids sorted that out. Their mortality rate was high, though the
Nautilus appreciated the variation in their diet...



At 15:12 01/06/19 -0400, you wrote:
> I have noticed that often salt water shelled mollusks in the aquarium
tend to have their periostracum degrade as well as the shell. One
particularly striking example was of a Charonia varigata that lost the
entire perio and the shell turned a grayish green. When the animal added to
the shell, that portion had the periostracum for a while and the shell had
the normal coloration, but gradually, the periostracum began to disappear
and then the shell began the degrade. The animal was healthy as far as we
could tell and the pH of the water was always monitored (I don't remember
what it was). I always wondered what the artificial lights did to the algal
growth - what bloomed more rapidly in the aquarium. Anyway, I'm not around
live animals right now and I don't know where my notes are, but I just
thought I would share this observation.