You’re not alone if you’ve ever wondered what a sponge actually is
Sponges, or porifera, do seem plant-like. They don’t really move and they don’t have muscles or organs. But they’re not plants.
Plants have chloroplasts, they make their own food by photosynthesis and their cells have walls. Sponges are filter feeders, they sift plankton from water that moves through pores in their bodies and their cells don’t have walls. And, although they can reproduce asexually like some plants, they can also reproduce with sperm and eggs, like animals.
Sponges are the oldest living animal phylum and represent some of the simplest animals on the planet. They also mark a critical step in evolution. Animals suddenly appear in the fossil record 540 million years ago in a period known as the Cambrian explosion. Scientists expect that animals probably appeared before then, but the identity of the first one is unclear.
A team at the University of California recently found a molecule called 24-IPC in 640-million-year-old rock. It was made by several organisms, including sea sponges. Evolutionary trees made by researchers from the Massachusetts Institute of Technology suggest that sponges might have been some of the first animals that ever lived.