In include amphids and phasmids; external organs made

In this lesson, we will learn briefly learn about the characteristics of a common roundworm ”Ascaris”. Then we will discuss the anatomy of ”Ascaris” including the senses, skin, muscles, body cavity, and digestive system.

Background Information

Image one day you got out to take a hike in the forest and when you take your first step, you are two feet off the ground because you are walking on top of debris from the trees and animals! This is what would happen if we didn’t have organisms like Ascaris that help consume debris! In this lesson we will learn about Ascaris and go over some background information.Ascaris is a genus of roundworms.

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There are many different species, but Ascaris lumbricoides is the most common. Ascaris worms are found in soil, saltwater, and freshwater, but are far more famous for being a parasite, making their homes in the intestines of horses, pigs, and humans. An infected person infected can suffer from malnutrition and loss of appetite, though usually not death.

Adult Ascaris, Female Ascaris on the left and male Ascaris on the right

External Anatomy

Ascaris worms have a cylindrical shape and are white or yellowish in color. The males are significantly smaller than the female, which range from 20-49 cm (over a foot long!) with a diameter of 3-6mm. Looking at Ascaris, they look very plain and simple, but upon a closer investigation you will see many different parts. First, let’s discuss their different senses.Senses are the way in which organisms understand their environment. We all know that humans have 5 senses: hearing, touch, smell, sight, and taste; Ascaris worms have two senses: the sense of touch or tactile reception and the ability to sense chemicals in the environment, known as chemoreception.

Ascaris worms have no eyes. Imagine if humans didn’t have eyes. Which of our other senses could help us avoid danger? Our hands could.

We could use our hands to touch and feel things around us to help determine if anything poses a threat. Ascaris worms don’t have hands, but they do have a labial papillae on the 3 lips of their triangle-shaped mouths. Labial papillae are hair-like structures used for tactile reception and are very sensitive to vibrations and touch, similar to the same way we use our hands.Another important sense Ascaris worms have is chemical reception. The parts of the body used for sensing include amphids and phasmids; external organs made up of only 6 cells that are used for chemical reception. Just like our nose is able to detect pheromones in the environment and indicate that we are sexually attracted to someone, Ascaris worms use amphids (located on the belly side) and phasmids (located near the anus on the female) to sense chemicals in the environment that indicate a potential mate is nearby.Next, we’ll discuss the skin and internal anatomy.

Skin and Internal Anatomy

Imagine if we had transparent skin. We would be able to see our heart beating and our muscles contracting when we walk, pretty cool right? Ascaris worms have very transparent skin that you can see through with your naked eye. But how can something that appears thin and weak protect the internal organs? Well, their skin consists of the cuticle and hypodermis.The hypodermis is the closest layer of skin to the internal organs.

Underneath the hypodermis is longitudinal muscles. Just like we can bend our arms and legs to move and appear shorter, longitudinal muscles contract and cause worms to look shorter and help with movement.The cuticle is the outer layer of skin that covers the hypodermis. The cuticle it is very thick and resistant to chemicals since Ascaris worms usually live in the intestines of a host. It also helps to maintain the structure of the body.

Another cool thing about Ascaris worms is that they are pseudocoelomates; ‘pseudo-‘ meaning false and ‘-coelom’ meaning body cavity. This ‘false’ body cavity contains the digestive system and is filled with fluid that can change in pressure to aid in movement. Ascaris worms therefore have a hydrostatic skeleton, which means they have a fluid-filled coelom surrounded by muscles that functions to support the body, help with locomotion, and disperse external forces.

Lastly, let’s discuss the digestive system.

Digestive System

Each part of the digestive system helps to move the food along to the next part in the digestive system until the waste is expelled. The digestive system includes the alimentary canal. The alimentary canal is the entire tube in which food enters in the mouth and eventually exits the anus.

In addition to the alimentary canal, the digestive system includes the mouth, pharynx, intestines, and rectum. The mouth and pharynx bring food into the body. The pharynx then passes the food along to the intestine where the nutrients from the food are extracted and the waste is passed on to the rectum for expulsion through the anus.

Lesson Summary

Ascaris worms are a very common roundworm that can live in the intestines of horses, pigs, and humans. They are a cylindrical shape and males are smaller than females.

Ascaris worms have labial papillae that are used for tactile reception and amphids and phasmids are used for chemoreception.Ascaris worms have very transparent skin that consists of the cuticle and hypodermis which protect it from the acids in the intestines of the host and assist with locomotion. They also have a ‘false’ body cavity so they are referred to as pseudocoelomates. The pseudocoelom gives rise to the hydrostatic skeleton which functions to support the body, help with locomotion, and disperse external forces.The digestive system includes the alimentary canal (the entire tube in which food enters in the mouth and exits the anus), mouth, pharynx, intestines, and rectum.

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