Some authors (e.g., Pennak) have noted that no animals are reported to feed
on freshwater sponges but this is not true. There is a fish in west Africa
that feeds almost exclusively on freshwater sponges. Also, closer to home,
some of the shiners in our southeastern blackwater streams feed on them
seasonally (e.g., coastal shiner, N. petersoni).
So sponges are probably worth experimenting with just to see if you can keep
them alive or to see who (if anybody) eats them.
Re freshwater feather dusters (polychaete worms) - the group is tiny but
apparently important as water quality indicators - I believe that the EPA
published a guide to the group back in the early 1970's as part of their
series of manuals on the identification of freshwater biota.
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