Eldrazi spawn squirmy, underdeveloped, mana-infused pupa. Eldrazi spawn are small - mere infants compared to the Brobdingnagian monstrosities they serve - but they serve an important role to the brood lineage. By some unknown process, greater Eldrazi can store consumed energy in their spawned underlings and then hatch greater Eldrazi by consuming the spawn in turn.
Each lineage has its own form of eldrazi spawn. The spawn of the Ulamog lineage are like squirming, miniature versions of the other creatures of the lineage. They have the skull-like bony plates over the head, the bifurcated arm structure, and the mass of colorful tentacles at its base.