Cecaelia are slimy, humanoid demons.
Cecaelia demons resemble blobs with somewhat human heads, except they possess close-set eyes and a triangular slit that serves as a mouth and nose. Their torsos are short and thin with no arms, and their lower halves end in a mass of tentacles of varying sizes. Cecaelia also produce copious amounts of slime that completely covers their bodies and interferes with their speech. They have sharp, slime-stained teeth and flickering green tongues that ends in a thick point.
In 1878, the warlock Magnus Bane summoned a cecaelia demon named Elyaas while searching for the demon that cursed Will Herondale, however he realised Elyaas was not the right demon as he was the incorrect color.
Magnus once again summoned Elyaas in 2007 as a job for Caroline Connor of Pandemonium Enterprises. Elyaas remained within a pentagram in Magnus's apartment until Connor returned, and they discussed Magnus' relationship with Alec Lightwood. Elyaas was sent back to the Void after Magnus found out what Pandemonium Enterprises needed him for and offered a better solution.
- Cecaelia demons, while not actually Greater Demons, are more individualised than lesser demons and have their own names and personalities.