Sponges are so much simpler and so different than other animals, that scientists first thought of them as plants. It wasn't until the 1850s that their cells were inspected and discovered to be animal cells.  What characteristic of animal cells differentiates them from plant and fungal cells?  What characteristic do you think scientists found that made them determine that sponge cells are in fact animal cells?  Think of the answer, then click "Show Me" to see if you are correct.

All animal cells lack a cell wall. Plant cells and fungal cells both have cell walls.

All animals in phylum Porifera lack body symmetry, thus they have asymmetrical body plans. This is a characteristic that they share with animals in phylum Placozoa. 

In order to understand the history of animals and how they came to be, one must first look into protists, a diverse group of organisms that are eukaryotic and mostly unicellular.  These organisms are divided into three different types--plant-like protists, fungi-like protists, and animal-like protists.  Biologists suspect that plants, fungi, and animals evolved from protists, and learning about their protistan ancestors helps us to understand more about the complexities of plants, fungi, and animals.  

Click each picture below to learn about some very important animal-like protists that all animals are linked to and that biologists suspect all animal life has evolved from, with sponges having the most obvious connection.