Phylum Arthropoda is the largest phylum in the Animal Kingdom. Some familiar organisms in this phylum are: lobsters, crabs, spiders, mites, insects, centipedes and millipedes (Barnes). The animals in this phylum are invertebrates that have an exoskeleton, a segmented body, and jointed appendages (“Arthropoda”). Arthropods can be seen in every habitat on Earth, including aquatic and terrestrial environments, and show a wide variety of adaptations (Barnes).
Feeding
Arthropods exhibit every type of feeding mode. Arthropods can be carnivores, herbivores, detritus feeders, filter feeders, or parasites. Arthropods typically have paired appendages around the mouth which are used to collect and handle food. These appendages are also usually specialized in accordance with the particular diet of the animal (Barnes). For example, the appendages of a butterfly and a spider differ because they live in different environments and thus have different needs. Butterflies have long narrow tube in their mouth called a proboscis (“What do Butterflies Eat”). A proboscis is useful to them because they use it to drink nectar, their primary source of food, from flowers. In contrast, carnivorous spiders capture prey with poison delivered with a pair of appendages and are able to maintain a firm grip on the prey thanks to their sharp teeth. They then rip the prey into small parts for consumption (Breene).
Digestion
Because there are millions of arthropods that live in different habitats and feed on different things, the digestive tract varies for each animal (“Feeding, Digestion and Excretion”). In general, however, most arthropods have three main regions: the foregut, midgut, and hindgut (“Phylum Arthropoda”).
Feeding
Arthropods exhibit every type of feeding mode. Arthropods can be carnivores, herbivores, detritus feeders, filter feeders, or parasites. Arthropods typically have paired appendages around the mouth which are used to collect and handle food. These appendages are also usually specialized in accordance with the particular diet of the animal (Barnes). For example, the appendages of a butterfly and a spider differ because they live in different environments and thus have different needs. Butterflies have long narrow tube in their mouth called a proboscis (“What do Butterflies Eat”). A proboscis is useful to them because they use it to drink nectar, their primary source of food, from flowers. In contrast, carnivorous spiders capture prey with poison delivered with a pair of appendages and are able to maintain a firm grip on the prey thanks to their sharp teeth. They then rip the prey into small parts for consumption (Breene).
Digestion
Because there are millions of arthropods that live in different habitats and feed on different things, the digestive tract varies for each animal (“Feeding, Digestion and Excretion”). In general, however, most arthropods have three main regions: the foregut, midgut, and hindgut (“Phylum Arthropoda”).
The foregut and the hindgut are lined with chitin. The foregut consists of the mouth, throat, and stomach. The food enters through the mouth. Salivary glands provide fluids and enzymes to the mouth for lubrication of the initiation of food breakdown. The food travels down the throat and esophagus into the stomach, where it is broken down further. The midgut consists of the intestines, where most digestion is carried out and the food is broken down into small molecules. The hindgut consists of the rectum, which reabsorbs water and salts, and anus, which excretes solid, undigested food (Carr).
Because each arthropod has a different digestive system according to their method of feeding and body structure, let’s take a look at three distinct arthropods: the grasshopper, crayfish, and spider.
The Grasshopper
Digestion starts at the mouth with chewing the food. Enzymes in the salivary juice that is excreted in the mouth work to begin the breakdown of food. The food is swallowed and enters the esophagus and then the crop. The crop stores the masticated food temporarily. Then, the food passes into the gizzard which acts as the grinding chamber. At the junction of the gizzard and the stomach is a valve called the pyloric valve, which allows the passage of only the thoroughly digested food into the stomach and prevents the regurgitation of food from the stomach. Next the food enters the stomach, where digestive enzymes, including amylase, maltase, invertase, tryptase and lipase, secreted by the gastric caeca act upon the food. Next, the digested food is absorbed through the stomach walls into the surrounding space which is called the hemocoel. From here, the energy from the food is transported to different body parts. In the hindgut, absorption of water takes place and the undigested food is formed into almost dry pellets. These end up being excreted through the anus (“Digestive System of Grasshopper”).
The Crayfish
The crayfish is a marine species of the Arthropoda subphylum Crustacea. What is unique about this arthropod is that is has a two-part stomach. The “cardiac” stomach is a large sac-like structure in which food is stored. This stomach also contains teeth that grind up food before sending it onward (“How Do Crayfish Digest Their Food?”). Posterior to it is the smaller “pyloric” stomach, where most of the digestion occurs (“Crayfish Anatomy”). This stomach is similar to the stomachs of humans and other vertebrates (“How Do Crayfish Digest Their Food?”). Digestive glands are located on each side of the pyloric stomach which produce digestive enzymes that break down the food even further (“Crayfish Anatomy”).
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The Spider
Spiders are the only animals that digest their food outside their bodies. After capturing and poisoning their prey with their venom, spiders expel digestive enzymes from their intestinal tract onto their prey. The enzymes break down its body tissues, and then the spider sucks up the predigested, liquid tissues. By repeating this process many times, spiders digest the entire animal (“Spider”). At the end, most spiders convert nitrogenous bases into uric acid, which can be excreted as dry material. Finally, spiders use Malpighian tubules to extract these wastes from the blood in the hemocoel and dump them into the cloacal chamber, from which they are expelled through the anus (“Arthropoda”).
Here is a video of a spider attacking its prey:
Here is a video of a spider attacking its prey:
Excretion
After digestion, solid, undigested food is excreted through the anus of the arthropod (“Feeding, Digestion and Excretion”). In insects, nitrogen-containing waste is removed by using a set of Malpighian tubules, slender projections from the digestive tract that are attached at the junction of the midgut and hindgut. As the fluid passes through the walls of the Malpighian tubules to and from the blood in which the tubules are bathed, nitrogenous wastes are precipitated as concentrated uric acid or guanine. These substances are then emptied into the hindgut and eliminated. Most of the water and salts in the fluid are reabsorbed by the hindgut and rectum and returned to the arthropod’s body. Malpighian tubules are an efficient mechanism for water conservation and were another key adaptation facilitating invasion of the land by arthropods (“Arthropods”).
Evolution of the Digestive System in Arthropods
The fact that arthropods are very different from one another shows that they have evolved greatly, but they do have some similarities, which suggests that they must have evolved from a common ancestor. The variation in digestive systems shows that arthropods must have evolved to fit their environment and efficiently capture their prey. For example, there are variations in the ways spiders capture their prey. Web-building spiders make webs out of silk to trap their prey, while spiders with well-developed eyes stalk and ambush their prey. In Class Insecta, mosquitoes have pointed mouthparts for piercing and sucking while grasshoppers have mouthparts that are well adapted for chewing. Therefore, mouth parts of different species in this phylum are highly modified depending on what they eat.
Here is a brief video that summarizes some of the information presented on this page:
After digestion, solid, undigested food is excreted through the anus of the arthropod (“Feeding, Digestion and Excretion”). In insects, nitrogen-containing waste is removed by using a set of Malpighian tubules, slender projections from the digestive tract that are attached at the junction of the midgut and hindgut. As the fluid passes through the walls of the Malpighian tubules to and from the blood in which the tubules are bathed, nitrogenous wastes are precipitated as concentrated uric acid or guanine. These substances are then emptied into the hindgut and eliminated. Most of the water and salts in the fluid are reabsorbed by the hindgut and rectum and returned to the arthropod’s body. Malpighian tubules are an efficient mechanism for water conservation and were another key adaptation facilitating invasion of the land by arthropods (“Arthropods”).
Evolution of the Digestive System in Arthropods
The fact that arthropods are very different from one another shows that they have evolved greatly, but they do have some similarities, which suggests that they must have evolved from a common ancestor. The variation in digestive systems shows that arthropods must have evolved to fit their environment and efficiently capture their prey. For example, there are variations in the ways spiders capture their prey. Web-building spiders make webs out of silk to trap their prey, while spiders with well-developed eyes stalk and ambush their prey. In Class Insecta, mosquitoes have pointed mouthparts for piercing and sucking while grasshoppers have mouthparts that are well adapted for chewing. Therefore, mouth parts of different species in this phylum are highly modified depending on what they eat.
Here is a brief video that summarizes some of the information presented on this page: