Sea sponge
Sponges are animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s of the phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

 Porifera (icon; meaning "pore bearer"). Their bodies consist of jelly-like mesohyl
The mesohyl, formerly known as mesenchyme, is the gelatinous matrix within a sponge. It fills the space between the external pinacoderm and the internal choanoderm...

 sandwiched between two thin layers of cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

s. While all animals have unspecialized cells that can transform into specialized cells, sponges are unique in having some specialized cells, but can also have specialized cells that can transform into other types, often migrating between the main cell layers and the mesohyl in the process.