You've probably heard of SpongeBob SquarePants, the cute yellow sponge, who lives in a pineapple and adventures with his friends in the underwater world. You may have also used a sponge, that soft, porous thing that can be used to wash dishes, wipe tables, take a bath, and so on. But did you know that a sponge is actually an animal, and a very magical animal.
Sponges are a primitive class of aquatic invertebrates belonging to the phylum of porous animals, with about 5,000 species.
They have no nervous system, digestive or circulatory systems, and are riddled with small holes and channels that pass through their bodies, relying on maintaining a constant flow of seawater through their bodies to obtain food and oxygen and remove waste from their bodies. They also don't have a fixed shape and size and can change their appearance depending on the environment and needs. They can even recombine their own cells for regeneration and replication.
Sponges are the first to diverge from the most recent common ancestor of all animals, are located at the very base of the evolutionary tree throughout the animal kingdom, and form sister groups with all other animals (i.e., eumetazoans).
This means that sponges are the closest animals to primitive life forms and the ones that are the most adaptable to a variety of environments. They can live in freshwater or seawater, from shallow to deep sea, from tropical to polar, almost everywhere. They play an important role in marine ecosystems, providing habitat and protection for many other organisms. Some sponges can also form symbiotic relationships with other organisms, such as corals, algae, bacteria, etc.
Sponges also have a lot of human use value, such as as cleaning utensils, thermal insulation materials, etc.
As early as ancient Greece, sponges were salvaged and their endoskeletons removed for cleaning. Later, with the development of the chemical industry, artificial sponges appeared, but the name sponge remained. Natural sponges are still available in some stores, and they are softer, more durable, and more environmentally friendly than artificial sponges.
So, why do sponges look like plants?
This is because their body structure is very simple, with no obvious organs and tissues, only two layers of loosely connected cells forming the body wall, surrounding the central body cavity to form a tubular body.
They also do not have significant motor capacity, and most species attach to the seafloor or other objects and can only regulate their orientation and position through the flow of water produced by flagellar cells. They also grow much like plants, and can be multiplied by branching, splitting, falling, etc., forming different forms and structures.
Sponges are amazing animals that, although they look like plants, have many animal characteristics. Although they are simple in structure, they can adapt to various environments and changes. Although they are inconspicuous, they have important significance for humans and nature. The next time you see SpongeBob SquarePants or use a sponge, think about their stories, and maybe you will have more admiration and curiosity about them.