The digestive tract is separated into several well developed organs: pharynx, esophagus, crop, gizzard, and intestine. The pharynx sucks in dirt which contains microorganisms and other possible materials to be used as food. This material is passed on through the esophagus and into a slightly muscular organ called the crop. Here the food is kept for a short while. The gizzard contains small grains of rock and sand that will mash the food into smaller pieces. Then this mash is delivered into the intestine where it its chemically digested and the materials are absorbed into the blood. The unused food is passed on through the earthworm's anus. This material is called castings and is a good fertilizer.
Megascolides Australis (Giant Gippsland Earthworm)
The Giant Gippsland Earthworm is an annelid that lives primarily in soil near water. The digestive system of this particular earthworm is very similar to that of other earthworms. The digestive system is divided into many regions, or segments, that each have a different function to it. The system contains of the pharynx, esophagus, crop, intestine, and gizzard. What happens is that the food, such as soil, is swallowed by the pharynx. The soil then passes through the esophagus, in which it has calciferous glands that release calcium carbonate to rid or empty the worm's body of excess calcium. Once it passes through the esophagus, the food moves into the crop where it is stored and eventually moves to the gizzard after that. The gizzard then uses stones that the worm eats to grind the food fully. The food moves into the intestines as gland cells in the intestine releases fluids to assist the digestive process. That intestinal wall contains blood vessels where the digested food is absorbed and transported throughout the rest of the body.
The Giant Gippsland Earthworm is a harmless worm that feeds primarily on soil that contains large amounts of organic matter such as decaying plants where they absorb nutrients from through their consumption. Their way of moving toward food largely consists of them burrowing in the soil to look for organic matter to consume. Also, with their feeding through the soil, they actually make the soil more porous, releasing water and air that will help plants grow, and its waste is used as a fertilizer to plants which is why its excretion is so useful to growing plants. The Giant Gippsland Earthworm is an endangered species that also relies on water as a source of breathing and feeding so that it can take in organic matter which can then be broken down in its digestive system. |
Arenicola Marina (Lugworm or Sandworm)
The lugworm is annelid that lives primarily in beaches or dunes and feed in the sand. The internal process of digestion in a lugworm is similar to that of an earthworm such as the Giant Gippsland Earthworm, but its feeding habits, styles, and ways of breaking down food are very different. The lugworm is similar to that of an earthworm in that it burrows into the ground in order to reach the nutrients embedded into the ground, except that for the lugworm, it is sand that they are burrowing into and not soil. What happens is that lugworms feed on different micro-organisms, detritus, and bacteria that are located in the sediment, or sand. They ingest this sediment in the burrow, leaving a depression or whole on the surface of the sand. Then, once the sediment is stripped of its useful organic content and matter, it is expelled by the worm, producing the characteristic worm cast. Lugworms also have statocysts, an organ of equilibrium happening especially among invertebrate animals and containing usually of a fluid filled vesicle in which are suspended statoliths, which allow the lugworm to always burrow head down and correctly direct themselves for feeding. It has also been shown that if an aquarium is tilted, the lugworm will compensate and change position so that it will lead in the right direction for feeding. All in all, these worms can make up 30 % of the biomass of a sandy beach and are burrowing annelids that are also protected by predators since their tail that lags off at the end can regenerate when cut off, making the lugworm a very suitable animal in its environment. |
Hirudo Medicinalis (European Medicinal Leech)
The European Medicinal Leech is an annelid that lives primarily in ponds and marshes and feeds in those environments. The digestive system of this leech is very different from that of lugworms or earthworms. The system is located in the dorsal position, apart from the mouth, which has a ventral position. The mouth, which opens at the base of the anterior sucker, has 3 half-moon shaped jaws, the free edge of which have numerous calcite teeth making the incision. These jaws cut through the skin of the leech's prey or victim, leaving a characteristic Y-shaped bite. Next, the pharynx, equipped with powerful muscles, is used to suck and swallow the blood. It is made, or evaginated, into the wound in order to absorb the blood. The wall of the pharynx contains numerous salivary glands, as well. Then, the stomach has 11 pairs of gastric caeca, with the longest of these in the posterior position. These structures, which are equipped with small valves, make it possible to hold the blood ingested, enabling the leech to store very large amounts of blood for vast periods of time, promoting the leech's capacity to fast. Lastly, the middle intestine is the active digestive zone and the short posterior intestine or rectum ends with the anus. The European Medicinal Leech is a blood-sucking leech that primarily feeds on mammal blood as well as amphibians and amphibian eggs. The feeding process is very simple in which the leech bites into the skin and penetrates it with its 3 toothed jaws. It then secretes salivary mucus to lubricate the area of the bite in order to promote the ingestion of the blood meal. These leeches are used in laboratories and hospitals primarily because they have the ability to suck the contaminated blood or infection out of a certain part of a person's body, hence why they are referred to as "medicinal leeches." |