Earthworm Anatomy And Morphology: For Biology Lovers

Earthworms are invertebrates as they do not have any backbone.

Earthworms have both male and female reproductive organs, and they lay their eggs in a cocoon after mating. An earthworm is a segmented organism with anatomical features that vary according to its species, which makes them also known as annelids.

Earthworms are also classified into two main groups, namely the segmented worms and the moniliform worms. Earthworm anatomy includes the earthworm's skin, which is made up of an epidermis that keeps moisture in the body, muscles that aid in the movement in various ways, and also contain structures that aid respiration.

After reading about earthworms' skin segments and how they reproduce, check the earthworm lifespan and goat hair.

Earthworm Digestive System

The earthworm species is very diverse, but their digestive system is generally the same. Food moves through the earthworm's gut, starting with its mouth and esophagus, which lead to the crop and gizzard.

Their digestive tract is divided into distinct regions: the mouth, crop, gizzard, and large intestine.

The mouth is the first region of the digestive tract, and it has a set of sucking and grinding teeth called mandibular glands. They are used for feeding, which is why they are called chewing worms.

The primary function of these glands is to provide lubrication to food as it moves through the earthworm body.

They secrete mucus that coats the food particles, which aids in digestion by "softening" or smoothing out food particles so that they can be digested more easily. The saliva that slices through this region helps break down challenging pieces of food by breaking down enzymes in food to be digested more quickly.

The crop is the largest region of the digestive tract. For worms to digest food, they must first chew it.

The crop contains thousands of tiny holes called pyloric caeca, which direct the food to be passed into the gizzard. Food passes through this region because of tiny hairs that extend into the stomach called cecal hairs. It also contains small contractile muscles that contract and move food around as it passes through this region.

The gizzard is a powerful muscular organ that moves food from the intestine towards the mouth by repeatedly contracting. The gizzard grinds food into tiny particles that two worms can use for gas exchange.

The large intestine is the main section of the digestive system. It has a vast number of sections called crypts. The crypts are lined with microvilli which are extensions of the cell membranes, enabling one worm to absorb nutrients from digested food through its body.

Earthworm Respiratory System

This species has an exceptionally well-developed respiratory system that oxygenates the air, produces carbon dioxide, and takes up water for excretion. For this reason, the earthworm is an essential contributor to the health of the soil.

The earthworm also excretes wastes that break down into plant nutrients.

The earthworms are herbivores that mainly feed on plant roots, decaying plant matter, or other worms. They are very effective at aerating soil, preventing erosion and runoff of topsoil by burrowing in it.

As they tunnel, they loosen the soil, releasing nutrients that are then available to other animals or plants. Earthworms also overwinter as adults, which aids the nutrient regeneration process.

The earthworm body comprises three main parts, the first segment, second segment, and the third segment, set off by the anterior and posterior segments known as the clitellum. The clitellum contains male and female reproductive tracts for mating.

The actual classification of earthworms are creatures with segmented bodies that have no limbs or specialized features other than their respiratory system.

Their ventral blood vessel system, which brings blood to the tail region, is characteristic of earthworms. They have an extensive circulatory system with paired arteries and veins to bring oxygenated red blood cells to the tail.

They have a heart consisting of two atria, one ventricle, and one complete circle of muscle fibers that contract during the atria's pumping action (concentric contraction). The conduction system is like that of humans; they are organized into both left and right-sided groups.

Earthworm Excretory System

These species have an amazing adaptation that allows them to conserve water when in dried-up areas. They use their bodies for water, excreting liquid waste that is caked by the dry soil and turned into nutrients for plants.

This process requires little energy because the worms don't need to work hard to transfer liquids from their bodies into the soil. Their behavior also helps prevent erosion and channel nutrients back into the circulation of the earth's ecosystem.

The main excretory organ for earthworms is Nephridia which is associated with the clitellum. The aperture of nephridium is distinct, located at the apex of the body segment but slightly off-center.

The aperture is provided with a solid muscular sphincter that relaxes, usually during the wet season when water pressure in the nephridial sac drops, allowing fluid to enter and collect in the sac. The excretory products consist of nitrogenous compounds, mainly ammonia and some urea, secreted into the surrounding soil through pores called nephridiopores (macro-pore respiration).

Earthworm bodies contain dorsal blood vessel and ventral blood vessel which run right up to its heart. It has a coelom which is made up of mesoderm and endoderm.

Earthworms have a gut system with few muscles that help move food from the digestive tract to the excretory system. It also contains a nervous system that features the nerve cells and nerve cord helps in their movement.

Its intestines are coiled with an open end to allow for the removal of solid waste. This solid waste is stored in the clitellum, where it is then eaten by animals.

Earthworms produce eggs in cocoons which are then fertilized by sperm provided by other earthworms. The earthworm has a "blood" system called hemolymph, in which it carries nutrients and oxygen throughout the body along with nervous system fluids.

Fascinatingly, the earthworms have five hearts which are positioned at their following body parts: two pumping hearts for pumping blood forward and backward in the ring of tube feet at their tail end; one heart for providing blood flow to the front part of the worm; one heart situated in its middle segment for feeding it with oxygenated blood and circulating food particles.

The last heart is located at the head part of the worm for providing oxygenated blood to the brain and brain cells.

These species contain three main vessels which fulfill the purpose of circulating the blood to all the parts of the earthworm's body.

These are a uterine vessel for providing blood to its reproductive cells, a capillary vessel for supplying oxygenated blood to the dew worm's other parts, and a conducting vessel for transporting any waste products from other organs into excretory tubes.

It should be noted that females have two uteruses and males only have one. The last part of their intestine, which acts as a garbage can for this animal, contains special fat-filled cells which release stored fat when the worm eats food.

The fat serves as a form of dietary energy used to build up body tissues and provides warmth for the worm during freezing weather.

Since the earthworms do not have any teeth, they use their mouth to eat food. They have very thin skin, called a cuticle, and it looks like the layer of skin on their bodies.

Earthworms eat soil by swallowing it and then passing it down to a stomach to digest, but they cannot take in food from the front of their mouth, so they push through the soil with their head to get the food from behind them.

This means that earthworms will search for food backward and forwards, meaning that Earthworms will eat anything such as sticks, stones, and other organic matter. The worm will not eat anything too hard, but they do not eat anything too soft. This means that although Earthworms cannot eat the topsoil, the harder soil is digested in the stomach.

Food is passed down from the mouth to the buccal cavity, then the esophagus to the pharynx, and then into the crop before it finally arrives at the stomach, where it is broken down.

The broken-down food is passed either directly into the intestine or through a storage part of the digestive system called GIT before passing into the intestine.

Worms need not pass wind, so they get rid of their carbon dioxide through their skin. They cannot get rid of nitrogenous wastes from their bodies in any other way, but they can pass these wastes out when going for a move in soil or when going out in search of a mate.

Earthworms also breathe through the lungs by moving in small gaps between tiny holes in their skin called spiracles. When an Earthworm breathes, it will disturb its surrounding air so that air can get to the organs it needs to go.

Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for earthworm anatomy, then why not take a look at earthworm reproduction or earthworm facts.