What is The least complex animal has no tissue?

The least complex animals are often considered to be sponges, belonging to the phylum Porifera. Sponges lack true tissues and organs, instead consisting of a simple structure made up of specialized cells that perform various functions. They are primarily composed of a porous body that allows water to flow through, facilitating nutrient absorption and waste removal. This simplicity makes them some of the most primitive multicellular organisms in the animal kingdom.