dived and photographed by a team mate. Taken from Kaptai Lake, Chittagong, Bangladesh
hi,
I think that you have attached the wrong photo, I can see only pebbles and amphibian eggs (frogs or toads, I think)!
regards
Giovanni
Muntasir,
Very nice photos, but even good photos have their limitations.
I am familiar with clionid boring sponges from my PhD work in Beaufort, North Carolina, USA the 1970's. These sponges have their ostia and oscula (incurrent and excurrent openings) located on papillae that extend above the general surface of the colony, and they can appear inflated as they do in your closeup photos. Indeed, a lot of the "papillae" in your closeup photos do appear to have single, large central openings (oscula?) and the photos of the entire colony certainly look like a sponge. If you haven't already, Google "Cliona sponge" and look at "images for cliona sponge" and you will see the resemblance.
Clionids are obligate borers, primarily in calcareous substrates: shells, coral, limestone. Such host substrates are essential. In the early growth stage (alpha), the papillae enable them to develop ventillation in spite of the fact that most of the surface of the sponge is buried in that calcareous substrate. The alpha growth stage is the most commonly seen and is exhibited by all species. Some species also exhibit a beta growth stage in which the sponge overgrows and encases the outside of the calcareous substrate, but leaves it largely intact. Some also exhibit a gamma growth stage in which there is massive outgrowth of the sponge and the substrate is largely destroyed except for a few fragments deep within the sponge. Even at this stage, they retain the papillae. If (big if!) what you have photographed is a clionid, it appears to be a beta stage, although the host substrate is not identifiable.
However, superficial resemblances can be deceiving. Clionids are not the only sponges to have papillae, and there are other kinds of colonial organisms that can resemble sponges (e.g. freshwater bryozoans: Google "Pectinatella"). What is very strange to me is that your photos are from Kaptai Lake, a freshwater body according to what I've read. All of the clionids that I have ever seen or read about are either oceanic or estuarine, not freshwater. So my best guess (not really a diagnosis) is that it might be a papillose freshwater sponge of some kind. I am familiar with freshwater sponges in North America (Spongillidae), and we don't have any resembling yours here.
Shriraj Jakhalekar is correct that the only way you can know for sure is to take a tissue sample, dissolve it, and do a microscopic examination for hard parts like siliceous spicules (in sponges) or statoblasts (in bryozoans), then identify the species from the characteristics of these using a good local taxonomic key. You may need local expert help for that if you don't already have a mentor.
If you can't identify them with a local key it's always possible that you have a new species for the location...something that was overlooked by previous investigators, something that was introduced from outside the region, or even something entirely new to science (a freshwater clionid?), but it takes a lot of digging and scholarship to ferret out those possibilities.
Good luck...and nice photography!
V. Guida
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