Snails’ internal anatomy is the second section of the article on the anatomy of snails; the first dealt with the exterior structure.
Snails’ internal anatomy is comprised of several intricate systems, such as the circulatory, respiratory, digestive, nervous, and reproductive systems. The visceral mass contains most of the snail’s organs.
Whether you are a student of biology or simply interested in the natural world, this article will provide a fascinating look into the anatomy of these remarkable creatures.
Quick Notes about Snail Internal Anatomy
| Scientific name | Consists of | Function | |
| Mantle | |||
| Mantle | Nacreous secreting cells Glandular cells Epithelial cells |
Repair and maintain the shell | |
| Mucous gland | Secretory cells | Reduces friction during movement, communication, and defense | |
| Digestive system | |||
| Esophagus
|
Inner mucosa layer, a middle muscular layer, and an outer connective tissue layer | Pushes the food toward the stomach | |
| Stomach | Inner lining of cells that secrete enzymes, a middle layer of smooth muscles, and an outer layer of connective tissue | Digestion | |
| Hepatopancreas (digestive gland) |
– | Helps in digestion and produces enzymes to detoxify harmful substances | |
| Intestine (guts) | – | Absorb nutrients from the digested food | |
| Anus | – | Excretion of waste material | |
| Respiratory system | |||
| Gills (aquatic species) Lung (land species) |
– | Breathing | |
| Nervous system | |||
| Central nervous system | Brain and a pair of nerves (Ganglia)
Nerve cord |
Controls internal organs | |
| Peripheral nervous system | Axons | Controls muscle movements | |
| Circulatory system | |||
| Heart | One atrium and one ventricle | Pumps the hemolymph | |
| Veins | Aorta and capillary | Responsible for pumping oxygenated hemolymph. | |
| Hemolymph (blood) | – | Crucial circulatory fluid that transports oxygen | |
| Reproductive system | |||
| Testes (in males) | – | Produce eggs | |
| Ovaries (in females) | – | Produce semen | |
| Gonopore | – | Opening through which reproductive cells and fluids are released during mating. | |
Visceral mass
The visceral mass of snails is the central part of their body that contains many of their internal organs, including the digestive, circulatory, and reproductive systems. It is located beneath the shell and is protected by the mantle, which is a thin layer of tissue that covers the outside of the visceral mass.
2.1. Mantle
The interior of the shell is lined with a thin layer of tissue called the mantle, which secretes new layers of calcium carbonate as the snail grows. The mantle tissue also plays a role in repairing and maintaining the shell throughout the snail’s life.
The mantle is located on the underside of the snail’s body and also forms the opening of the shell, known as the aperture, through which the snail extends its body.
The mantle is a key component of the snail’s anatomy and is critical for the growth and protection of the snail’s shell.
2.2. Mucous gland
The anatomy of the mucous glands of snails can vary depending on the species and the location of the gland.
Note: In some snails, the mucous glands are concentrated in the foot, while in others they may be present in the mantle or other parts of the body.
These glands produce thick, sticky mucus that is composed of a complex mixture of glycoproteins, water, and electrolytes. Mucus serves a variety of important functions for the snail.
- One of the primary functions of the mucous glands is to provide lubrication for the snail’s movement. The mucus reduces friction between the snail’s foot and the surface it is moving on, allowing it to glide smoothly over rough or uneven terrain.
- The mucus produced by the mucous glands also helps to protect the snail from dehydration, infections, and other environmental stressors.
- It also plays a role in communication and defense. Snails use their mucus to leave chemical trails that can be followed by other snails, helping them to locate food or mates. The mucus can also contain defensive chemicals that deter predators or parasites.
2.3. Digestive system
Snails have a relatively simple digestive system compared to other animals, but it is still quite efficient at extracting nutrients from their food. The digestive system of a snail begins with the mouth, which is located on the underside of the head.
Esophagus
After the food is ingested, it passes through the esophagus and into the stomach for further digestion.
The esophagus in snails is a muscular tube that connects the mouth to the stomach. The esophagus is lined with muscles that contract and relax to move the food along and push it toward the stomach.
It is a part of the digestive system that plays a crucial role in the ingestion and transportation of food.
Stomach
In the stomach, the ingested food is mixed with digestive enzymes and broken down further.
While the stomach of a snail is a simple blind sac that continues the process of digestion with the help of saliva, the majority of the digestion occurs in the main digestive gland known as the hepatopancreas.
The digestive gland produces enzymes and other substances that aid in the digestion of food and also play a role in detoxifying harmful substances that the snail may ingest. Basically, this gland, which takes up most of the space in the visceral sac, acts as both the liver and pancreas in the snail’s digestive system.
Unlike the liver in other animals, the snail’s hepatopancreas not only produces digestive fluids and stores nutrients but also plays a key role in the digestion process.
From the stomach, the food moves into the intestine, where nutrients are absorbed into the body.
Intestine
The intestine is responsible for absorbing nutrients from the digested food that enters it from the stomach.
It is a long, coiled tube that is located in the visceral mass of the snail, next to the main digestive gland, or the hepatopancreas.
Any waste material that is left after nutrient absorption is eliminated from the snail’s body through the anus.
Excretion
In reality, snails do not have a true anus like many other animals.
Instead, waste material is excreted from the body through a small opening called the pneumostome, which is often located on the right side of the snail’s body near the mantle cavity.
2.4. Respiratory system
Snails are gastropod mollusks that breathe air, despite living in water or on land. However, due to the differences in their habitat and lifestyle, aquatic and land snails have different respiratory systems.
Aquatic snails
Aquatic snails breathe using gills, which are specialized structures that extract oxygen from the water. These gills are located inside the mantle cavity, which is a cavity located between the visceral mass (internal organs) and the shell.
The mantle cavity contains a network of small blood vessels, called the respiratory epithelium (highly vascularized tissue), which is responsible for the exchange of gases.
The snail pumps water into the mantle cavity and then expels it out through a siphon. As the water flows over the gills, oxygen is extracted and carbon dioxide is released.
Land snails
In contrast, land snails breathe using a simple lung, which is a highly vascularized sac located near the heart.
The snail takes in air through a small opening called the pneumostome, which is located on the side of the body. The air enters the lung and oxygen diffuses into the bloodstream, while carbon dioxide diffuses out of the bloodstream and into the lung to be expelled through the pneumostome.
Interesting fact: Although aquatic snails rely exclusively on gills for respiration, some land snail species are also capable of partial breath through their skin, especially when the humidity is high.
2.5. Nervous system
The nervous system of snails is relatively simple. It is composed of a network of nerve cells or neurons that are connected to sensory receptors throughout the body, as well as to muscles and other organs.
The nervous system of snails can be divided into several main components, including:
- the central nervous system (CNS)
- the peripheral nervous system (PNS).
The CNS is composed of the brain and a pair of nerve cords that run the length of the body, while the PNS includes sensory neurons that detect stimuli and motor neurons that control muscle movements.
CNS. The CNS is comprised of the brain, which serves as the central processing center, and a pair of nerve cords that run the length of the body. These nerve cords are responsible for carrying information to and from the brain, and they play a critical role in the snail’s ability to sense its environment and respond to it appropriately.
PNS. The PNS is made up of sensory neurons that detect various types of external stimuli and motor neurons that control muscle movements.
Together, these components (CNS and PNS) allow the snail to respond to its environment in a coordinated and effective manner.
Brain
The brain of snails is located near the front of the body and is divided into several distinct regions. These regions are responsible for processing different types of sensory information, such as visual and olfactory cues, and for controlling various behaviors and movements.
Nerve cords
The nerve cords of snails run along the length of the body, and are connected to ganglia, or clusters of nerve cells, that control specific functions such as feeding, locomotion, and reproduction. The ganglia are also connected to the sensory and motor neurons of the PNS, allowing the snail to respond quickly to changes in its environment.
The nerve cord is responsible for transmitting electrical impulses throughout the body to facilitate communication and control between various organs and tissues.
One unique feature of the nervous system of snails is the presence of giant axons, which are specialized nerve cells that are several times larger in diameter than other neurons in the body. These giant axons are responsible for controlling rapid muscle movements, such as those involved in the snail’s escape response.
2.6. Circulatory system
Snails have an open circulatory system.
The heart of a snail is a muscular structure located in the area above the digestive system, and it consists of one atrium and one ventricle.
Instead of blood, snails have hemolymph, which is a fluid that serves a similar function. The hemolymph carries oxygen and nutrients to the organs and tissues and also removes waste products.
In the snail’s circulatory system, hemolymph flows from the heart into the hemocoel, a cavity in the snail’s body where the organs are located. The blood then bathes the organs and tissues directly before returning to the heart.
2.7. Reproductive system
Snails can reproduce sexually through two main categories: hermaphroditism and dioecy/gonochorism.
- Hermaphrodite snails have both male and female reproductive organs and may be either simultaneous or sequential hermaphrodites.
- Dioecious or gonochoristic snails have separate sexes, with individuals being either male or female.
The reproductive system of a snail is located in the visceral mass, which is the internal organs of the snail. The reproductive system of a snail typically consists of both internal and external organs.
Internal organs include the testes (in males) and ovaries (in females), which are responsible for producing sperm and eggs, respectively. These organs are located in the visceral mass of the snail’s body, and they are connected to the external environment via a structure known as the gonopore.
In hermaphroditic snails, the gonopore is typically located on the side of the snail’s body near the head. During mating, two snails will approach each other and extend their reproductive organs from their bodies. Sperm is then exchanged between the two individuals, allowing each snail to fertilize the other’s eggs.
After fertilization, the snail’s eggs will develop into a shelled embryo known as a “capsule.” The capsule is usually deposited in a moist, protected area, such as under a rock or in a crevice. Depending on the species, the snail may lay a few large capsules or many small ones, and the time required for the eggs to develop can also vary.
Interesting fact: Some species of snails also have a specialized structure called a love dart, which is a small, sharp structure that is used during mating. The love dart is produced by the male reproductive organs and is thought to increase the chances of successful fertilization by altering the reproductive tract of the recipient snail.
In Conclusion
The anatomy of snails reflects the diverse habitats and survival strategies of these creatures. From their specialized glands that produce mucus to their intricate nervous systems and intricate reproductive structures, snails have evolved a variety of adaptations to thrive in different environments.
By understanding their anatomy, we can gain a deeper appreciation for the complexity and diversity of the natural world.