Title: Smaller Ecdysozoans
1Smaller Ecdysozoans
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3Diversity
- Many protostomes possess a cuticle
- Non-living outer layer secreted by epidermis
- Cuticle restricts growth and must be molted via
ecdysis - Members of Ecdysozoa molt cuticle as they grow
- Regulation of molting achieved by the hormone
ecdysone
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5Phylum Nematoda Roundworms
- 12,000 species have been named
- As many as half a million may exist
- Found in virtually all habitats in all biomes
- Topsoil may contain billions per acre
- Nematode parasites exist in nearly all animal and
plant species
6Phylum Nematoda Roundworms
- Form and Function
- Outer body covering is a thick, noncellular
cuticle, secreted by the underlying epidermis-
hypodermis - Cuticle serves to contain the hydrostatic
pressure exerted by fluid in the pseudocoelom - Collagen is the primary protein in layers of the
cuticle - Muscles
- Longitudinal muscles lie beneath the cuticle
- No circular muscles
- Run in four bands, marked off by epidermal cords
that project inward to pseudocoelom - Unlike other animals, the muscle extends to the
nerve cords
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8Phylum Nematoda Roundworms
- Hydrostatic skeleton-muscle contractions press on
fluid - No circular muscles to compliment longitudinal
muscle in movement (antagonist) so the cuticle
assists. - Fluid is force to opposite side when longitudinal
muscles constrict forcing the cuticle to expand - Compression and stretching of the cuticle returns
the body to resting position when muscles relax - Produces the thrashing movement of nematodes
9Phylum Nematoda Roundworms
- Digestion
- Gut tube consists of mouth, pharynx, non-muscular
intestine, short rectum and anus - Muscular pharynx sucks food in
- Intestinal wall is one cell thick-no muscles
- Food moves back as new food enters and the body
moves - Defecation occurs from opening the anus and
allowing pseudocoelomic pressure to expel waste - Some parasitic adults have an anaerobic
metabolism aerobic metabolism are absent - Free-living nematodes and free-living stages of
parasitic nematodes have both anaerobic and
aerobic metabolism
10Phylum Nematoda Roundworms
- Ring of nerve tissue and ganglia around the
pharynx give rise to small nerves to the anterior
end and to two nerve cords, one dorsal and one
ventral - Sensory organs at head and tail
- Most are dioecious with males smaller than
females - Male has copulatory spicules
- Fertilization is internal
- Nematode sperm has no flagella, in female
reproductive tract sperm is ameboid and moves by
pseudopods - Eggs are stored in uterus until deposited
- Cuticle is shed between each of four juvenile
stages
11Figure 12_03
12Representative Nematode Parasites
- Representative Nematode Parasites
- Some are parasites of humans
- Most are tropical
- Ascaris lumbricoides
- Occurs in up to 25 of people in some areas of
the southeastern U.S. - More than 1.27 billion affected worldwide
- A. suum is found in pig intestines
- A female Ascaris may lay 200,000 eggs a day,
which pass out in hosts feces
13Figure 12_04a
14Representative Nematode Parasites
- Survive for long periods in soil
- When humans eat undercooked vegetables
contaminated with shelled juveniles, or when
children put soiled fingers or toys in their
mouths, consumed juveniles hatch, and burrow
through intestinal wall - Carried through the heart to the lungs, they
enter into alveoli causing pneumonia and are
carried up to tracheae - Coughed up and swallowed, they mature in the
intestine - They feed on intestinal contents and may block
the intestines
15Figure 12_04b
16Representative Nematode Parasites
- Hookworms
- Anterior end of these small worms has a hook-like
curve - Necator americanus, most common hookworm.
- Sexes are separate
- Large plates in mouth cut into intestinal mucosa
and suck hosts blood - Pump through more blood than they digest
- Heavy infections cause anemia
- Eggs pass out in feces and juveniles hatch in
soil - If human skin comes in contact with soil,
infective juveniles burrow through skin to blood - Travel in blood to the lungs, are coughed up to
be swallowed, and mature in the intestine
17Figure 12_05
18Representative Nematode Parasites
- Trichina Worm
- Trichinella spiralis causes a potentially lethal
trichinosis - Adult worms burrow into intestinal mucosa of the
hosts small intestines and females directly
produce juvenile worms - Juveniles penetrate blood vessels and circulate
throughout the body to all tissues and spaces - Penetrate skeletal muscle cells, redirecting gene
expression of the musculature - Cells lose striations and becomes a nurse cells
to the parasite - When poorly cooked meat (pork or bear) containing
encysted juveniles is swallowed, worms are
liberated and mature in the intestine
19Representative Nematode Parasites
- Infect humans, pigs, rats, cats and dogs
- Pigs can become infected eating uncooked scraps
of infected meat or rats - Four other sibling species with variable
distribution, freezing resistance, etc. - Heavy infections cause death
- 25 cases of trichinosis are reported per year in
the US
20Figure 12_06
21Representative Nematode Parasites
- Pinworms
- Most common worm parasite in the U.S.
- Adults live in large intestine and cecum
- Females, about 12 mm in length, migrate to anal
region at night and lay eggs, causing itching - Scratching the anal region contaminates hands and
bedclothes - Eggs develop rapidly and become infective within
six hours at body temperature - When swallowed, hatch in duodenum and mature in
large intestine - Members of this order have haploid males from
unfertilized eggs - Females are diploid and come from fertilized eggs
(haplodiploidy)
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23Representative Nematode Parasites
- Filarial Worms
- Eight species of filarial nematodes infect humans
- Some cause serious diseases
- Wucheria bancrofti and Brugia malayi live in
lymphatic system - Cause inflammation and obstruction of the
lymphatics vessels - Females release live young, tiny microfilariae,
into blood and lymph - Mosquitoes ingest microfilariae when they feed
- Worms develop to infective stage and move into
the mosquito bite wound when it bites a human - Elephantiasis is caused by repeated exposure
- Swelling and growth of connective tissue causes
enormous swelling of body parts-scrotum, legs,
arms
24Representative Nematode Parasites
- River blindness or onchocerciasis is carried by
black flies and infects 37 million people in
tropics - Dog heartworm, Dirofilaria immitis, is carried by
mosquitoes and is the most common U.S. filarial
worm - Heartworm pills
25Figure 12_08
26Figure 12_09
27Representative Nematode Parasites
- Dracunculus medinensis, the guinea worm
- Larvae live within planktonic copepods (water
fleas) - Upon ingestion of contaminated water, water fleas
are digested by human host, but larvae survive
and penetrate the stomach/intestinal wall - Worms live and mate within body cavity
- Gravid females migrate through tissues to the
lower extremities and produce an open ulcer - Causing burning pain, the human host immerses leg
into water and female releases thousands of eggs
into water - Eggs are eaten by copepods and the cycle
continues
28Representative Nematode Parasites
- Only known treatment is to carefully remove
ulcerated females carefully with a stick treated
this way for thousands of years
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30Phylum Nematomorpha
- Diversity
- Horsehair worms resemble coarse hairs
- Adult structures resemble those seen in
nematodes cuticle, epidermal cords, only
longitudinal muscles, and a similar nervous
system pattern - Currently placed as the sister taxon to nematodes
- About 320 species are known
- Occur worldwide
- Adults are free-living in moist habitats
- Juveniles are parasites of arthropods
31Phylum Nematomorpha
- Larvae encyst within host and do not emerge from
an aethropod host unless water is nearby - Juveniles of freshwater forms use terrestrial
insects as hosts - Marine nematomorphs infect certain crabs
-
- Digestive system is vestigial
- Larvae absorb food from arthropod hosts
- Adults can absorb organic molecules through
vestigial gut and body wall
32Figure 12_10
33Phylum Tardigrada
- Known as water bears
- Very small, less than 1 mm long
- About 900 live in a water film around mosses and
lichens - Some live in freshwater and some are marine
- Most are terrestrial that occupy a film of water
surrounding mosses and lichens - Trunk bears eight short unjointed legs, each with
claws - A pair of stylets and sucking pharynx protrude to
pierce nematodes or plant cells - Body covered by non-chitinous cuticle that is
molted four or more times during lifetime - Most of the body cavity a hemocoel
- No circulatory or respiratory systems
-
34- Cryptobiosis
- Terrestrial tardigrades can suspend metabolism to
survive harsh conditions - Tardigrades can dehydrate from 85 water to only
3 water - In this state they can resist extreme
temperatures, ionizing radiation, oxygen
deficiency, etc. for years - When water is available, they become
metabolically active again
35- Reproduction
- Sexes are separate
- In parthenogenetic freshwater and moss-dwelling
species, males are unknown
36Figure 12_15
37Phylogeny and Adaptive Diversification
- Phylogeny
- Evolutionary relationships among ecdysozoans are
not well-understood - Members of this clade do not share a common
cleavage pattern - Nematodes and nematomorphs
- Cleavage is unique, not spiral or radial
- Cleavage in tardigrades
- Has yet to be studied
38Phylogeny and Adaptive Diversification
- Recent phylogenies place Nematoda and
Nematomorpha as sister taxa since they share a
collagenous cuticle
39Phylogeny and Adaptive Diversification
- Tardigrades have some similarities to rotifers,
particularly in their reproduction and
cryptobiotic tendencies - Tardigrades and arthropods also share
arthropod-type setae and muscles inserted on the
cuticle
40Phylogeny and Adaptive Diversification
- Adaptive Diversification
- Nematodes show the most impressive adaptation
- Found in almost every habitat available to
animals - Body structure is plastic enough to allow
adaptation - Life cycle ranges from simple to complex
- Have been known to survive in suboptimal
conditions