Nematoda Roundworms Body Cavities Pseudocoelomate General Characteristics Nema

Nematoda Roundworms

Body Cavities

Pseudocoelomate

General Characteristics Nema greek for thread Unsegmented Triplobastic: ectoderm, mesoderm, endoderm Bilateral symmetry Pseudocoelomate 12, 000 species known actual abundance may be closer to 50, 000 species. • Habitat (everywhere) • • • – Marine – Freshwater – Terrestrial (polar to tropics) • Very abundant – Good topsoil may contain billions of nematodes per acre

General Characteristics cont… • Feeding Habits – Saprozoic- feeding on dead or decaying matter – Corprozoic- feeding on feces – Carnivorous o Size o Placentonema gigantissima, was a little over 27 feet long o It was discovered inside the placenta of a sperm whale. o Nematodes can be as small as 0. 01 inches.

Form and Function Cylindrical shape Tapered at both ends Muscles run longitudinally only Use fluid-filled pseudocoel as a hydrostatic skeleton • Tough cuticle • • – secreted by the underlying epidermis

Digestive System o Complete digestive system. o Their digestive system can be divided into three parts o. Stomodeum- consists of the “mouth and lips”, buccal cavity, and the pharynx (esophagus). o. Intestine functions by digesting, absorbing water and nutrients, and eliminating the residues of digestion. o. Proctodeum serves as the anus and is where waste is excreted.

Nervous System o Set of neuronal processes that run lengthwise o These ganglion connect to the nerve ring which surrounds the esophagus.

Reproduction Methods o Males are smaller than females and have a bent tail for holding the female for copulation. o During copulation, spicules are inserted into the genital pore of the female, enabling amoeboid sperm to crawl along the spicule. o Eggs may be embryonated or unembryonated, meaning that they may not yet be developed.

Defense Mechanisms o The cuticle is the flexible outer covering which acts as an exoskeleton, allowing the nematode to maintain internal stability. o It is formed by secretion of the hypodermis. o The hypodermis is a thin cellular layer underlying the cuticle. o The cuticle functions as a barrier, a sensory array, and as a hydrostatic skeleton. o As a barrier it provides protection. o As a as sensory array it detects changes. o As a hydrostatic skeleton it acts as an antagonist to longitudinal muscles.

Crop damaging nematodes

Gongylonema pulchrum nematode

Ascaris lumbricoides: large roundworm of humans • 1. 4 billion people currently infected • Lives in the small intestine • Female may be a foot long and produce 200, 000 eggs a day • Infection occurs when parasite eggs are eaten with uncooked food or when soiled fingers are put into the mouth. • In the intestines the worms cause abdominal symptoms and allergic reactions and may produce an intestinal blockage.

Male (top) and 9. 8 female Ascaris lumbricoides

Hookworms • Anterior end curves dorsally into a hook • Large plates in mouth cut through intestinal wall so facilitate blood sucking • Anti-clotting factors in saliva • Small • Mobile • Often cause – Anemia – Stunted growth

Hookworm life cycle

Trichinella spiralis: Trichinosis • 2. 4% of the US population is infected • Adults live in the small intestine; Juveniles travel all over in the body eventually penetrating skeletal muscle – manipulates the host cell’s DNA causing the cell to recruit a blood supply to supply food to the cell and also produce collagen to form a cyst around the cell. • Heavy infections-lethal • Light infections- soreness, fatigue • Undercooked pork or other omnivores – – – Foxes Wolves Skunks Bears Raccoons Rats

Pinworms • Most common helminth parasite in the US – 30% of children – 16% of adults • Live in the large intestine and feed on bacteria and feces • Females migrate to the anus to lay eggs at night • Host scratching moves the eggs to hands and bedclothes • Eggs are infective at 6 hours at body temperature • Diagnosis “The Scotch Tape Method”

Wuchereria bancrofi: Filarial worms • 250 million people infected (tropical) • Worms live in the lymphatic system and cause obstruction • Spread by mosquitos • Elephantiasis- repeated filarial infections – Excessive growth of connective tissue – Enormous swelling of affected parts (arms, legs, genitals, and breasts)

http: //en. wikipedia. org/wiki/File: Filariasis_01. png

Elephantiasis of leg caused by filarial worms 9. 12

Dirofilaria immitis: Dog heartworm • Most common filarial worm in the US • Carried by mosquitos • Infects canids (dogs), cats, ferrets, sea lions and occasionally humans • 45% of all dogs in the Gulf states are infected

Diriofilaria immitis Dog heartworm 9. 13

http: //www. plymouthmosquito. com/dog_heartworm. htm

Fun Facts o Nematodes are the most abundant multicellular organism. o Some Nematodes can undergo cryptobiosis. o In cryptobiosis the nematodes alter their metabolism in response to a drastic environmental change (like freezing or extreme heat). o Essentially, the nematodes shut down their bodies and “wake up” when conditions are habitable again. o Would you like to take a guess at how large the biggest nematode ever recorded was? o Placentonema gigantissima, was a little over 27 feet long! o It was discovered inside the placenta of a sperm whale. o Nematodes can be as small as 0. 01 inches. o They can be found in places like Antarctica and oceanic trenches. o One handful of soil contains thousands of roundworms