BI256 Study Guide - Final Guide: Endothermic Process, Merostomata, Omnivore

280 views48 pages
15 Apr 2017

For unlimited access to Study Guides, a Grade+ subscription is required.

Animals Exam Review
Chapter 18: Nematodes
Ecdysozoa Possess a cuticle, which is a nonliving external layer secreted by the epidermis
Cuticle: stiff, hardened outer body wall that restricts growth and must be molted via ecdysis
(Synapomorphy between ancestors)
Molt cuticle as they grow
Regulation of molting is achieved by hormone ecdysone (hormone associated with growth)
Do not share common body plan with Lophotrochozoan
Members of Nematoda, Nematomorpha, and Kinorhyncha are pseduocoelomates (don’t have a
true coelomic cavity)
The pseudocoelom is used as a hydrostatic skeleton in nematodes, kinorhynchs, and priapulids
while loricifera species vary from being pseudocoelomate and acoelomate
World of
Most important pseudocoelomate animals, both in abundance and impact on man
Found in soil, oceans, freshwater habitats, plants, and all kinds of animals
About 25,000 species- due to new grouping half a million species may exist
Found in all habitats in all biomes such as good topsoil may contain billions of nematodes per acre
Found in all animal and plant species, making nematode infestation studies important in
agriculture and biomedical sciences
Free-living feed on bacteria, yeasts, fungal hyphae, and algae while some are saprozoic or
coprozoic (live in feces material)
Predatory nematodes eat rotifers, tardigrades, small annelids, and other nematodes
Important as food for mites, insects larvae, and nematode eating fungi
elegans in
Model for studies of genomics and cell development and differentiations
Origin & lineage of 959 cells in body been traced from zygote- adult (eutely=fixed # of somatic
Complete wiring diagram of CNS is known-all neurons and all connections between them
Genome mapped and completely sequenced (3 million base pairs and 19.820 genes)
Form and
Outer Body
Distinguishing characteristics: express eutely, a set number of cells
Cylindrical shape, non-segmented, bilaterally symmetrical
Flexible, nonliving cuticle is shed during juvenile growth stages
Lack motile cilia/flagella, except for one species
Lack protonephridia. Gland cells/canal system opening to excretory pore for excretion
Pharynx is muscular with a triradiate lumen (important for feeding)
NO respiratory or circulatory systems (rely on diffusion for gas exchange)
Covered in thick, noncellular cuticle secreted by the underlying epidermis (hypodermis)
Cuticle is shed during juvenile growth stages
Hypodermis is syncytial with nuclei located in four hypodermal cords that project inward
Dorsal & ventral hypodermal cords bear longitudinal dorsal and ventral nerves, and the lateral
cords bear excretory canals
Cuticle has 3 layers of crisscrossing collagen, providing elasticity but restricting lateral expansion to
allow for hydrostatic pressure when fluid is exerted from pseudocoelom
Hydrostatic skeleton- a non-compressible fluid enclosed and pressurized in a body cavity
Longitudinal muscles only- 4 fields of longitudinal muscles contract in groups producing local
find more resources at
find more resources at
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 48 pages and 3 million more documents.

Already have an account? Log in
Direct Life Cycle
Have no circular muscles
Pseudocoelomic fluid is incompressibleinternal pressure increasesstretching of muscle cells in
another part of the body
Local contractions of the muscle fields: dorsal and ventral longitudinal musculature act as
antagonists, producing sinusoidal waves along the length of the nematode’s body (sigmoidal wave)
Alimentary canal consists of mouth, pharynx, non-muscular intestine, short rectum and anus
Pharynx sucks food via rapid contraction of anterior body and opening of lumen
Relaxation of muscles closes lumen & enables food to move into intestines
Food moves back as new food enters and the body moves around
Defecation by opening the anus and allowing high Pseudocoelomic pressure to expel waste
Most are dioecious with males smaller than females
Fertilization is internal where eggs are stored in uterus until deposited
Development is usually direct for most free-living forms
Cuticle is shed between each of 4 juvenile stages
Parasitic forms have free-living juveniles that may require intermediate hosts to complete their life
Parasitic nematodes exist in every major animal group from sponges-mammals
Nematodes parasitize other nematodes as well as roots, stems, leaves and flowers of plants
General Characteristics
1.Economic importance: medical (humans), companion animals, livestock, crops
2.Extensive migrations within vertebrate hosts
3.Parasitic nematodes attain greater sizes than non-parasitic
4.Enormous reproductive capacities
-Direct (single host) indirect (additional intermediate hosts)
-Eggs or larvae- in feces or urine
-First stage/third stage are infective and may be “free living”
-L5 is the immature adult stage-only an adult once you start reproducing
L1 molts to L2 and L3 stages in the intermediate host
Definitive host ingests the intermediate host, maturation of adults, mating and eggs/larvae
The Large
Roundworm of
Direct life cycle, occurs up to 225% of people in southeastern U.S
Female may lay 200,000 eggs a day, which pass out a host’s feces
Embryos develop into infective juveniles in 2 weeks but can be killed by direct sun and heat
Eggs have tolerance to adverse conditions, can tolerate desiccation or lack of oxygen
Shelled juveniles survive for long periods of time in soil, sometimes even years
Infection can occur when eggs are ingested with uncooked vegetables or when children put soiled
fingers into their mouth
Unsanitary conditions contribute to higher infection rates as soil and drinking water may be
“seeded” from infected individuals
Host swallows embryontated eggs, then juveniles hatch which then burrow through intestinal wall
to get to veins and lymph vessels
Juveniles move through the heart and to the lungs, then break into alveoli and are carried up to
trachea which may cause pneumonia
At the pharynx, juveniles are swallowed and mature in the intestine after 2 months
Feed on intestinal contents and may block or perforate the intestines and exit anus
find more resources at
find more resources at
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 48 pages and 3 million more documents.

Already have an account? Log in
Infection rates tend to be higher in children and males who are more likely to ingest soil
Small worms have anterior ends with hook-like curves
Sexes are separate with males being smaller
Large plates in mouth cut into intestinal mucosa and suck host’s blood
Blood is pumped through intestines partially digesting it and absorbing the nutrients
Since hookworms suck more blood than they digest, heavy infections can cause anemia
Children can suffer mental retardation, stunned growth and lack of energy
Eggs pass out in feces and juveniles hatch in soil and live on bacteria
If human skin meets infested soil the infective juveniles burrow through skin to get to the blood
Infective juveniles then travel in the blood to the lungs, are coughed up then to be swallowed and
goes to stomach and intestines
Juveniles mature in the intestine much like those of Ascaris sp
Causes a potentially lethal trichinosis
Adult worms burrow into intestinal mucosa and females directly produce juvenile worms
Juveniles penetrate blood vessels and circulate throughout the body to all tissues and spaces
Penetrate skeletal muscle cells and can become one of the largest intracellular parasites
Juveniles can redirect gene expression of host cell musculature where cells lose striations and
comes a nurse cells to the parasite
When poorly cooked meat containing encysted juveniles is eaten, worms are liberated and mature
in host intestine
Can infect humans, hogs, rats, cats and dogs
Hogs can become infected when eating uncooked scraps of infected meat/infected rats or their
T.spiralis has 4 other sibling species with variable distribution, infectivity to various hosts, and
freezing resistance
Heavy infections cause death but lighter infections are more common worldwide
find more resources at
find more resources at
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 48 pages and 3 million more documents.

Already have an account? Log in

Get access

$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
1 Booster Class