Source: The Lost Outpost, pg(s). 88-89
Thalassic architects more closely resemble veiled masters than they do standard aboleths. They are about 15 feet long and weigh 2,800 pounds. They have five eyes; four are set to either side of their head, while a larger fifth eye is set in the centre and glows brilliant white. Thalassic architects have four tentacles, two of which end in claws capable of manipulating objects, while the others can be vibrated at a frequency so high that the tips can carve glyphs in solid stone. Dark bands of scales typically ring their silvery bodies.
Thalassic architects were created when the rulers of the alghollthus realised that they have the ability to perform certain physical tasks without lesser beings to assist them. Not content to become dependent on servant races, alghollthus bred a new subspecies to fulfill this role. The first thalassic architects could move and shape only earth and stone, leaving the tedious labour to the skum. After thousands of years of evolution, modern thalassic architects can break apart and reassemble matter on a minute level, enough to seize control of countless individual water molecules.
Thalassic architects have fundamentally different brains from others of their kind. They can only alter the perceptions of other creatures, unable to overwhelm their consciousness. Their powers of illusion are seated in the portion of the brain directly behind the central eye, suggesting this eye is responsible for snaring enemies' attention.
In the past, thalassic architects were considered to be only useful but crippled and odd mutants by standard aboleths. This position has since improved, due to the growth of their power and their low numbers.
Alghollthus rely on thalassic architects to oversee construction. A typical crew is led by a thalassic architect assisted by standard aboleths, who direct the skum slaves. When the architecture is too complex for skum to build efficiently, the thalassic architect personally completes the structure.