The auxiliary cell is critical in the post-fertilization development of many red algae.

They provide nutritive support to developing oocytes (young eggs) and participate in forming the vitelline envelope. Characteristics: These cells are 20–30

Auxiliary cells are specialized intra-gonad cells found in the female acini (gonadal follicles) of certain marine organisms.

In some species, this cell is part of a specialized, branched structure called an "auxiliary cell ampulla".