How could mollusks be manipulated to control their shell growth?

Question

I wanted to create an alien species that mostly relies biomaterials and biotechnology and one method of growing hard materials could be controlling the growth of seashells. The alien mollusks will be based on earth mollusks for this question.

At the earliest stages when the species is as advanced as stone age man, they could manipulate the mollusks whilst in shallow water to create simple structures. When they evolve into an advanced species they could have mineral rich vats of liquid with complicated shell structures being created which can be used for many purposes or even combined with other biological material to give other useful properties.

At first the alien species will try to manipulate the shells into small tools, around the same size as the shell would be and they will try to make large (possibly curved) sheets of shell. The larger sheets may need multiple mollusks working together or breeding much larger mollusks but either way they will need to be manipulated or tricked into making the shells these different shapes.

How can this alien species when at the stone age level, manipulate the mollusks to make these different shell structures?

Answer 1

I think they could an approach similar to beekeeping mixed with coral growth.

They would start by letting a species similar to coral grow on simple square frames, from where they take out the mineral deposited by the outgrowing coral, and use it as a base for further manipulation.

Later on they can use more complicated forms to have the coral-like species grow on, depositing the mineral.

Having a coral instead of a mollusc will ensure smaller pores of the resulting material.

Answer 2

Nacre pearled tools:

Your stone-age aliens inadvertently invented composite materials. Early in their history, they made symbolic tools and gave them as "offerings" to their gods by placing them inside of giant mollusk shells. The mollusks coated these objects with nacre, essentially turning them into cultured pearls.

Now your aliens could make any small tool they could produce into a hard-yet-flexible, durable artifact that was also extraordinarily beautiful. In THIS question, the use of nacre as bone material was discussed. It's an outstanding material with amazing qualities, and combined organically with other materials they start out with composites in the stone age. They soon discover that crushed shell material formed together with bio-glue has the glue slowly replaced and the entire object becomes nacreous. As their techniques advanced, the found they could make parts of an object, then weld the nacreous objects together with nacre paste and placing the weld sites inside of shells. Varying the composition and structure of the coated objects allowed items with different properties. Eventually, they select for mollusks that don't even HAVE shells, but that coat anything they are placed on with nacre, allowing large and complex parts to be built.