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Re: Green gobs

> It was a soft - nearly gelatinous - translucent,  chlorophyll-green
> about an inch across.  One side was lumpy and wrinkled like a  brain.
> other side was concave and appeared to have been previously attached
> something.  My kids were wading around just upstream from where I
found it
> floating and I speculate that they dislodged it. 
> My first reaction was that it was some type of algae, and my second
> it may have been some simple critter with an algal symbiont, or maybe
something like a 
> freshwater sponge with algae growing in or on it. 

I think you nailed it--a freshwater sponge.  Many species are green due
to the presence of inter- and intracellular algae, resulting from a meal
and/or symbiosis.  Very few sponge species are limited to one type of
growth form, so identification by shape and size is rarely feasible.
Sponges are typically identified by the shape of their microscopic
spicules that help support its  tissues.

If not a sponge, it could be a colonial bryozoan, but I've never heard
of one bright green.  One of my references states "Bryozoa are among the
most difficult of all fresh-water invertebrates to culture in the
> At any rate, I brought it home and placed it in a brightly 
> lit, unfiltered tank, tied down to a stone with a length of fine 
> monofilament.  A any idea what the thing might really be, and if so,
then how I might 
> better keep it?

Reefkeepers are able to keep sponges, so I don't see why you can't
either.  I suspect growth might be limited by SiO2 in your tank,
however.  Otherwise, I think you are on the right track.

> Third:
> I've long been interested in keeping filter-feeding critters in
> unfiltered planted tanks.  I noticed that Arizona Aquatic Gardens
> mussels.  I assume these are freshwater mussels, or at least that they
> don't really care.  I have a tank where I've been successful keeping
> but I remember someone on this list (Mark Fisher, possibly?)
> that mussels really can't be kept in an aquarium.

I don't recall saying that, but I think it would be difficult to keep a
mussel.  It would have to be in an unfiltered tank, and preferably one
that produces a lot of detritus.  Some mussels can filter particles as
small as one micron in diameter, so they can be pretty efficient filter
feeders.  Also, they burrow and move around, so they would definitely
disturb your substrate.  Longevity is variable, with some species living
only 1 year while others can live 15+ years.  If you have very soft or
acid water, calcium deficiency could be a problem.  I wouldn't keep a
mussel with any of my favorite fish, because by the time you notice the
mussel has died, your fish probably have also.