Digestive System in Vertebrates and Invertebrates: Types of Digestion and Feeding

Digestive System of Vertebrates

Digestive system of vertebrates: The digestive system of vertebrates is formed by a digestive tube that contains the mouth, pharynx, esophagus, stomach, and intestine, along with accessory glands: salivary glands, liver, and pancreas.

3. Ingestion of food

There are two types of ingestion:

• Passive ingestion: Occurs in aquatic animals with specialized structures. Sponges have structures formed by cells with cilia and ciliated flagella that facilitate the ingestion of food. The flagella beat in a wave-like pattern, drawing water in and trapping food particles. Some algae, bivalves, and marine worms and molluscs have their outer surface of the gills covered by cilia that cause movements that draw water into the internal palial cavity, where the gills filter the water and retain the food particles.
• Active ingestion: Organs adapted to capture and hold food. Adaptations of this type include:
  • Radula of molluscs: a structure with numerous small teeth that moves like sandpaper to scrape plant material.
  • Tentacles of cephalopods: muscular structures with suckers, and in some cases, cells that aid capture.
  • Cnidarians: have urticating cells with stinging fluid that paralyze prey and facilitate its capture.
  • Buccal appendages of arthropods: morphological structures that vary according to the nature of the animal's diet.

Teeth of vertebrates triturate food, cutting and grinding it. Each tooth has one root.

Digestive System of Some Invertebrates

• Platyhelminthes: Planarians have a digestive tube with a single blind-ended opening serving as mouth and pharynx; the tube branches within the intestine and absorbs food.
• Annelids: The earthworm has a long tube running the length of its body, formed by a pharynx, esophagus, crop, gizzard, intestine, and anus. The gizzard crushes the food.
• Molluscs: Esophagus, stomach, intestine, mouth, and anus, along with the voluminous hepatopancreas gland, which secretes digestive enzymes into the stomach and intestine.
• Echinoderms: The digestive tube is continuous, beginning at the mouth with a short esophagus and a short stomach, and continuing into the intestine, ending at the anus. Sea urchins have Aristotle's lantern, a structure of five teeth used to scrape food.
• Arthropods: Insects have a digestive tract beginning at the mouth, which receives secretions from short salivary glands; the esophagus leads to the intestine, which ends at the anus. Crustaceans have a hepatopancreas and a gastric mill, a structure with three teeth used to triturate food.