What most people know about invertebrates usually has to do with their unique development, evolution, and the fact that they have no regular skeletal structure to support their bodies. However, an equally important and unique fact about invertebrates that is, however, far lesser known, is that they have quite unique digestive systems and eating patterns. Most invertebrates will, in fact, eat almost anything that is or was alive. While some prefer the role of predator, others prefer to ambush their prey, and some get even more creative about how they handle their daily menu.
Invertebrates generally have a very wide array of eating habits, ranging from eating small plants and dead things, to consuming rotten fruit. There are detritivores, herbivores and carnivores throughout the invertebrate world, and many animals actually enjoy combining their food in a large variety of ways. Cuttlefish have one of the most unique, as well as toughest mouths, being able to eat crustaceans and to catch crabs with their 10 large tentacles. Freshwater shrimp keep the water clean by eating small dead plants, while ragworms shoot out strong jaws to catch small creatures crawling through the mud and sand.
There are many secrets that the wide world of invertebrates hides when it comes to the actual methods of hunting and feeding that most species employ. Their unique abilities have made them adapt to a wide range of environments, so that many of them have evolved to perfect a few incredibly efficient feeding methods. Spiders build elaborate webs that entice and capture their prey, while sponges are known as filter feeders. Periwinkles scrape seaweed from rocks, and they prefer a menu of dead plants, while starfish are actually active predators. Many of the world’s parasites are also invertebrates. Living on (or inside) the bodies of their hosts, they usually feed off them, while using elaborate and creative methods of switching from one host to another.
These diverse forms of feeding and elaborate forms of hunting have evolved over millions of years. Invertebrates are basically some of the oldest species on the planet and they were also the first actual animals that have ever evolved. Since the earliest fossils of invertebrates have been found dating back to more than 600 million years ago, these unique animals had a very long time to adapt to the many changes that the climates and habitats they thrive in have undergone.
Invertebrate digestive systems are built according to the role and feeding needs of each individual species. The simplest type of digestive system consists of a gastrovascular cavity that features a single opening used for both feeding and excretion. Other, more evolved forms of invertebrates feature more elaborate alimentary canals that begin with a mouth and go through an esophagus, crop, and intestines, used in the process of extracellular digestion. While most invertebrates have evolved to use only intracellular or extracellular digestion, there are a few unique phyla that actively use both systems.