Squamosa are typically kept in the sand bed because of their low light demands. With that said, and the fact that they have one of the widest byssal ports in a tridacna clam, they should be protected. Place a small flat rock or clam shell under the clam. This protects the "soft spot" of the clam from worms and other critters that would otherwise use that spot as a port of entry. If you put yours back on a solid substrate (either the rock or shell), it should quickly emit byssal fluids and eventually they will harden to threads.
What you may have seen is the byssal fluids before they actually hardened to create the threads. Sometimes, it mixes with sand, or other small particles of substrate and look like a slimey glob if they are not on a hard surface.
Do you have something under your squamosa? If not, you should try it. Not only will you help it by protecting the byssal port, but you will probably make the shellfish happier if, in fact, it is attempting to adhere to something.
Dave