28.5 Superphylum Ecdysozoa: Nematodes and Tardigrades
The annelids are the earthworm, leech, and featherduster.
The featherduster worm is a tube-dwelling filter-feeding polychaete.
There is a large number of species in the superphylum.
The roundworms and the arthropods are two of the most diverse animal groups.
The ecdysozoans are protected from water loss, predators, and other dangers of the external environment by their flexible and tough cuticle.
The Tardigrada has exceptional resistance to desiccation and other environmental dangers.
The members of this superphylum periodically go through a process called ecdysis, in which the old exoskeleton is shed.
The old cuticle is replaced by a new one, which will last until the next growth period.
The Nematoda are triploblastic and have an embryo sandwiched between the ectoderm and the endoderm.
They are bilaterally symmetrical, meaning that a longitudinal section divides them into the right and left sides.
Nematos are pseudocoelomates and have a circular cross-section.
Nematodes include both living and dead forms.
If all the matter in the universe were swept away, our world would still be dimly recognizable, and if we could investigate it, we should find its mountains, hills, vales, rivers.
According to nematologists, there may be over one million unclassified species.
The name Nematoda is derived from the Greek word "Nemos," which means "thread," and includes all true roundworms.
Nematodes are abundant in all habitats.
Caenorhabditis elegans has been used as a model system for many different avenues of biological inquiry in laboratories all over the world.
The mouth and anus of these animals are different from the flatworms'.
A rectum and anal opening can be found at the back of the mouth.
A multinucleated tissue is formed by the fusion of many single cells.
The pharynx and rectum are the ends of the digestive tract.
The anterior mouth opening in the head is made up of three or six "lips" and teeth from the cuticle.
Rings, head shields, or warts are some of the modifications that may be presented by some nematodes.
The external rings do not reflect true internal body segmenting, which is a hallmark of Annelida.
The attachment of the muscles of nematodes is different from that of most animals, because they have a longitudinal layer only, and their direct attachment to the nerve cords creates a strong muscular contraction that results in a whiplike, almost spastic, body movement.
The soybean cyst nematode is shown in the electron micrograph.
Nematodes do not have well developed excretory systems.
Nitrogenous waste is released across the body wall.
osmoregulation and salt balance can be performed by simple excretory cells or glands that are connected to a pair of canals.
There are four longitudinal nerve cords that run along the length of the body.
The ventral nerve cord is more developed than the other cords.
There is a fusion at the tail.
Depending on the species, Nematodes use a variety of reproductive strategies.
C. elegans is a mostly monoecious species with both self-fertilizing hermaphrodites and some males.
Ova and amoeboid sperm are contained in the uterus and spermatheca, respectively.
The vagina is an external opening of the uterus.
The male genital pore is closer to the tip than the female genital one.
The copulatory spicules at the tail of the male keep him in place and open the vagina of the female into which the amoeboid sperm travel.
embryo development starts very soon after fertilization.
The embryo is released during the gastrulation stage.
The development of a young adult worm begins at the embryonic stage, which lasts for 14 hours.
Adverse environmental conditions can lead to the formation of an intermediate stage known as the dauer larva.
The body of a given species contains a specific number of cells as the result of a rigid developmental pathway.
Biologists would need to design three different experiments if they wanted to research nicotine dependence, how lipids are regulated, and the attractiveness of odors.
They might only need to study Caenorhabditis elegans.
The C. elegans was brought into the focus of mainstream biological research by Dr.
The animal has been used as a model system to study many different mechanisms.
There is a free-living nematode in the soil.
Researchers can observe and monitor changes within the animal with ease thanks to its transparency.
It has about 1,000 cells and only 20,000 genes.
Its chromosomes are arranged into five pairs of autosomes and a pair of sex chromosomes, making it an ideal candidate to study genetics.
This organisms is useful for studying cellular phenomena like cell-to-cell interactions, cell-fate determinations, cell division, and cell death.
The short life cycle of this worm is an asset.
It takes three days to get the "egg to adult to daughter egg", so the consequences of genetic changes can be quickly identified.
The life span of C. elegans is two to three weeks.
There are two genders in this species.
Since both parents need meiotic nondisjunction when they are XX, it's rare for males from hermaphrodites to be obtained.
The position and number of the 959 cells present in adult hermaphrodites of C. elegans is constant, which makes it an excellent experimental model.
This feature is very important when studying cell-to-cell communication.
The usefulness of C. elegans as a model system is rounded off by its ability to be manipulated with genetic methods.
Information banks and groups dedicated to research using C. elegans have been created by biologists worldwide.
Their findings have led to better understandings of cell communication during development, neuronal signaling, and insight into lipid regulation, which is important in addressing health issues like the development of obesity and diabetes.
Studies have shown a better understanding of polycystic kidney disease.
This simple organisms has led biologists to complex and significant findings, growing the field of science in ways that touch the everyday world.
There are 959 cells in these hermaphrodites.
Under ideal conditions, the nematode spends a set amount of time at each juvenile stage, but it may enter a dauer state that does not age significantly and is somewhat analogous to the diapausing state of some insects.
There are a number of common parasites.
These economically and medically important animals have complex life cycles that involve multiple hosts and can have significant medical and veterinary impacts.
Humans may become colonized by Dracunculus medinensis, known as guinea worms, when they drink water containing copepods, an intermediate crustacean host.
Animals, especially dogs, cats, and humans, can be affected by hookworms.
Humans can get trichinosis from the consumption of undercooked pork, and other mammals can also get it.
The roundworm Ascaris may cause physical obstruction of the intestines by stealing nutrition from its human host.
The filarial worms, such as Dirofilaria and Wuchereria, can be transmitted by mosquitoes to mammals.
Over 120 million people worldwide are affected by Wuchereria bancrofti, a disease that causes a non-lethal condition called elephantiasis.
In this disease, parts of the body swell to huge proportions due to inflammation of the lymphatic tissues.
The dog heartworm species is Dirofilaria immitis.
The slow-steppers are small animals that live in marine, freshwater, or damp environments throughout the world.
Water bears are called "water bears" because of their plump bodies and large claws on their legs.
Most of the species are less than 1mm in length.
The body may be divided into plates with a chitinous cuticle.
They can survive the loss of up to 99% of their water content.
Their remarkable resistance has recently been attributed to unique proteins that replace water in their cells and protect their internal cell structure and their DNA from damage.