Sponges vs Cnidarians
One interesting difference between sponges and cnidarians is that sponges lack tissue while cnidarians have tissues but not the organ systems. Sponges and Cnidarians are very primitive acoelomic invertebrates with very simple body structures. Both organisms are found in aquatic ecosystems. Sponges and Cnidarians have no organ systems. In this article, we will see the specific features of sponges and cnidarians and, from that, we will deduce the differences between sponges and cnidarians.
What are Sponges?
Sponges are aquatic animals with a simple hollow asymmetrical body and categorized under Phylum Porifera. Phylum Porifera includes about 7000 identified species. Some examples for sponges include barrel sponges, boring sponges, basket sponges, bath sponges, etc. Most species are marine and very few live in freshwater. Adults are sessile and have an asymmetrical bodies. Sponge body is composed of two layers; outer flattened cell layer and inner flagellated collar cell line, which opens to its internal cavity. In between these two cell layers, there is a gel-like extracellular matrix. In most sponges, this matrix secretes fibrous protein that acts like an exoskeleton. Unlike other animals, sponges have intracellular digestion. Sponges feed on planktons by filtering water. Sponges are hermaphrodites. Their sperms are released into the water and eggs are stored in their body. The larva is free-living and motile. Sponges are harvested from the sea by humans and used for bathing and cleaning.
What are Cnidarians?
Cnidarians construct the life’s largest construction known as coral reefs. Cnidarians (Phylum Cnidaria) include jellyfish, sea anemones, corals, Hydra, and sea fans. There are about 10,000 species found in this phylum. The key characteristic features of cnidarians include radial symmetry, acoelomate body with tissues, lack of organs, and the simple digestive sac that opens through a mouth, which is surrounded by tentacles armed with nematocysts.
All cnidarians are carnivores and have very simple body structures adapted as predators. Most of them live in marine ecosystems, and very few species live in freshwater. Cnidarians have no reproductive, digestive, circulatory, or excretory systems. Moreover, they have a very primitive nerve net with nerve receptors, which are sensitive to touch, gravity and light. The only unique feature of cnidarians is the presence of nematocysts, a specialized cell for capturing their prey and for defense.
What is the difference between Sponges and Cnidarians?
• Phylum:
• Sponges belong to Phylum Porifera.
• Cnidarians belong to Phylum Cnidaria.
• Characteristic Feature:
• Sponges have intracellular digestion and lack tissues.
• Cnidarians have nematocysts.
• Food:
• Sponges capture planktons by filtering water through their cells.
• Cnidarians are predators and feed on small fish, krill, etc.
• Presence of Tissues:
• Sponges lack tissues.
• Cnidarians have tissues but no organ systems.
• Body Symmetry:
• Most sponges have asymmetrical bodies.
• Cnidarians have radially symmetrical bodies.
• Cell Types:
• Sponges have few types of cells.
• Cnidarians have a wider range of cell types.
• Species Diversity:
• There are about 7000 species of sponges.
• There are about 10,000 species of sponges.
Images Courtesy:
- Sponge by CC BY-SA 4.0)
- Cnidarians via Wikicommons (Public Domain)
