Lower metazoa, also known as invertebrates, exhibit a wide range of feeding and digestion patterns. Here are some common patterns observed in different groups of lower metazoa:
1. Porifera (sponges): Sponges are filter feeders that obtain nutrients by pumping water through their bodies and filtering out organic particles. They have specialized cells called choanocytes that create water currents and capture food particles.
2. Cnidaria (jellyfish, corals, sea anemones): Cnidarians have a central body cavity called the gastrovascular cavity, which serves both as a digestive and circulatory system. They capture prey using specialized stinging cells called cnidocytes and then release digestive enzymes into the gastrovascular cavity to break down the food.
3. Platyhelminthes (flatworms): Flatworms have a simple digestive system with a single opening called the mouth. They can be free-living or parasitic, and their feeding strategies vary accordingly. Some flatworms are predators, while others are scavengers or feed on organic matter in the environment.
4. Nematoda (roundworms): Roundworms have a complete digestive system with a separate mouth and anus. They feed on a variety of materials, including bacteria, fungi, plants, and other animals. Some nematodes are parasites that live inside the bodies of other organisms.
5. Annelida (segmented worms): Annelids have a well-developed digestive system with a mouth, pharynx, esophagus, crop, gizzard, and intestine. They exhibit diverse feeding habits, including filter feeding, deposit feeding, and predation. Some annelids, like earthworms, ingest soil and extract nutrients from organic matter present in it.
6. Mollusca (snails, clams, squids): Mollusks have a specialized feeding structure called the radula, which is a rasping tongue-like organ used for scraping food particles. They have a complete digestive system with a mouth, esophagus, stomach, and intestine. Mollusks exhibit various feeding strategies, including herbivory, carnivory, filter feeding, and scavenging.
7. Arthropoda (insects, crustaceans, spiders): Arthropods have a diverse range of feeding and digestion patterns due to their immense species diversity. Insects have specialized mouthparts for different feeding habits, such as chewing, sucking, or sponging. Crustaceans have a complex digestive system with a foregut, midgut, and hindgut. Spiders inject digestive enzymes into their prey and then suck out the liquefied contents.
These are just a few examples of the feeding and digestion patterns observed in lower metazoa. The diversity of feeding strategies in this group is vast, reflecting the wide range of ecological niches occupied by these organisms.