Sponges

Leon is at the beach, when he finds something washed up on the shore. It’s yellow, round, and full of holes. Do you know what it is Leon? It’s a dead sponge! Sponges are animals for two reasons: they can’t produce their own food, and the nuclei of their cells are surrounded by a membrane.

The kind of sponge Leon found on the beach is not the only kind: sponges come in many different shapes, sizes, and colours! They may be round, shaped like tubes, cones, or fans; they can be brown, red, yellow, orange, violet, or dark grey. Despite their differences, they have a lot in common - so much, that we classify them into the same larger group of animals, phylum Porifera. So, what are the characteristics of this phylum? They are multicellular organisms, which means they are made up of many specialised cells.

One type are the porocytes which make up the holes, or pores, on the sponge’s body. Water flows in through the pores, and is then pumped around the sponge and finally out of it, by another type of cell; The collar cells, choanocytes, which line the channels inside the sponge. At one end, the collar cells have a long, whip-like structure, the flagellum. When flagella on these cells move, they push water through the channels of the sponge. When water passes the collar cells, these filter out nutrients, and this is how the sponge gets food!

But water doesn’t just bring nutrients, it also brings in oxygen, and takes away waste and carbon dioxide. These specialised cells take over the role that in more complex animals would be done by various types of tissues and organs: respiration and digestion. Another characteristic of sponges is that they are invertebrates, which means they don’t have a spine or vertebral column. All sponges live in water, and they are a really important part of marine and freshwater ecosystems. They are food for animals like turtles, but also provide shelter for other organisms, like algae and some crustaceans.

But fishing, coastal development, and climate change threaten these animals that have existed on Earth for hundreds of millions of years. We need to protect the environment, so that organisms like these can continue to exist, and enrich our planet’s ecosystems.