When the amoebas of slime molds join they form structures with many nuclei called

The right answer is Plasmodia.

Plasmodia is a mass or part of cytoplasm that has pultinucleate (ie composed of several nucleus instead of one). This property is characteristic of certain species, such as slime molds or moldy molds.

Viscous molds have several characteristics of fungi, but do not have hyphae. They are made of amoeboid cells without walls. The spores of viscous molds are surrounded by cellulose walls. Mushroom spores are made of chitin or another polysaccharide.

Plasmodia is your answer! XD