Phylum Nematoda and other Pseudocoelomate Animals, Chapter 9, Zoology

Phylum Nematoda (Roundworms) Name (nematos) means a thread One of the most abundant types of worms in the world. 12,000 species named, estimated 500,000 species worldwide yet to be discovered. Live in a wide variety of habitats. Ocean, freshwater lakes and streams, soil, from the poles to the equator. Good topsoil may contain billions of nematodes/acre. Parasitize almost every type of plant and animal. Most average about 5 cm (2 inches) in length. However, they range in size from being microscopic to some almost 1 meter in length.

Nematode Anatomy and Locomotion Nematodes move by using fluid pressure generated in their pseudocoelom. This fluid-filled chamber that provides structure and locomotion is called a hydrostatic skeleton. Hydrostatic skeletons work by transferring the force of muscular contractions to a non- compressible fluid (hydraulic fluid pressure). The pressure is contained by a thick, elastic cuticle made of collagen.

Nematodes Hydrostatic Skeleton In some animals like earthworms, circular muscles and longitudinal muscles work together to expand and contract. Circular muscles are absent in nematodes. Longitudinal muscles work antagonistically against the outer cuticle like a spring. When the longitudinal muscles contract, the cuticle on the opposite side is stretched. When the longitudinal muscles relax, the cuticle relaxes and the body cavity returns to its original shape. This causes nematodes to move erratically.

Nematode Pseudocoelom and Longitudinal Muscles

Nematode Digestive System The digestive system of nematodes is complete but simple, consisting of a mouth, pharynx, intestine, rectum and anus.

Nematode Nervous System The Nematode nervous system consists of a ring-shaped ganglia at the anterior end of the body that connects to two nerve cords that run the length of the body.

Nematode Reproduction Most nematodes are dioecious (males and females are separate sexes). They exhibit sexual dimorphism; males are usually smaller than females. Fertilization is internal and eggs are stored in the uterus. Eggs are deposited by the female, embryo develops, juvenile hatches from an egg. There are four juvenile stages, and each juvenile stage is separated by a molting or shedding of the cuticle.

Nematode Reproduction

Nematode Parasites

Ascaris lumbricoides Common name human intestinal roundworm. One of the most common worms in humans. Up to 25% of the southeastern US is infected and over 1 billion people in the world. Approx. 20% of the world's population. Females can grow up to 30 cm long (1 foot). Females produce up to 200,000 eggs a day. Adults live in the small intestine and eggs leave the host's body in the feces.

Ascaris lumbricoides People become infected with ascarid worms when uncooked vegetables are eaten or when children put fingers or toys in their mouths. Worm eggs are extremely resistant to harsh conditions other than direct sunlight and high temperatures. They can survive in soil for months and sometimes even years. When eggs are consumed they hatch in the host's intestine, and penetrate the intestinal wall to reach the host’s bloodstream.

Ascaris lumbricoides After reaching the host's bloodstream the juveniles make their way to the lungs. Once worms reach the lungs, the host can develop a serious case of pneumonia. After the juvenile worms are coughed up, they are swallowed into the digestive tract and make their way back to the intestine where they become sexually mature. Large numbers of adults cause intestinal blockage and severe abdominal pains.

Ascaris lumbricoides

Hookworms Hookworms get their name from their anterior end which curves like a hook. They burrow their hook mouths into the intestines of humans and suck blood. Can cause anemia in people and can delay mental and physical growth in children and cause a loss of energy. Life cycle and transmission is similar to ascarid worms (intestinal roundworms).

Hookworms

Trichinella spiralis Responsible for the potentially fatal disease called trichinosis. Females produce live young. Juveniles penetrate skeletal muscles where they burrow and develop into cysts in the muscle tissue called nurse cells. Transmission occurs when meat from an animal containing nurse cells is ingested, the juvenile worms are liberated into the intestine where they mature.

Trichinella spiralis

Pinworms Cause very few symptoms but are the most common worm parasite in the United States. Estimated 30% of children and 16% of adults have pinworms in the United States. Adults live in the large intestine. Females migrate to the anal region of a human host at night to lay eggs. Scratching contaminates hands and bedsheets. Eggs can then be transmitted and swallowed. Contamination can be tested by using the “scotch tape method”.

Filarial Worms About 250 million people infected worldwide, mostly in tropical countries. Causes obstruction and inflammation of the lymphatic system. Mosquitos can carry the disease and extreme manifestations can cause elephantiasis. Elephantiasis is a condition caused by swelling of certain parts of the body such as the legs, arms, and genitals.

Filarial Worms The most common form of filarial worm in the US is the dog heartworm. Carried and transmitted by mosquitos. Can also infect cats, ferrets, sea lions and occasionally humans.

Phylum Rotifera Pronounced ro-tif' e-ra Name means rota – wheel fero – to bear, the wheel-bearing animals. The name comes from their ciliated crown called a corona. When the corona beats, it has the appearance of a rotating wheel. They range in size from 40 micrometers to 3 mm but average size is between 0.1 mm to 0.5 mm.

Rotifers

Rotifer Ecology Rotifers are cosmopolitan, which means they are found all over the world. Most rotifers live on the bottom of freshwater lakes or ponds, some are marine and terrestrial. Most rotifers eat plankton. Some rotifers are parasitic and epizoic (live on the surface of other animals).

Rotifer Anatomy Rotifers have a head, trunk, and foot. The corona leads to the mouth. The mouth leads to a muscular pharynx called a mastax. Their telescoping foot can attach to substrates by secreting a sticky substance that is produced by pedal glands in their foot and their toes.

Rotifer Anatomy

Phylum Acanthocephala Pronounced (a-kan'tho-sef'a-la) Name means acantho – spine or thorn, cephala – head. Aka spiny-headed worms. Acanthocephalans get their name from a proboscis that can be protruded and bears many rows of spines which attach to the intestinal wall a host. All acanthocephalans are endoparasitic. Most parasitize fish, birds, and mammals.

Phylum Acanthocephala