Transcript Worms - Cloudfront.net

Marine Worms
Bilateral Symmetry
Cut body one way = 2
identical halves
 (bi = two, latus = side).
 Orientation includes:
– Anterior
– Posterior
– Dorsal
– Ventral
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Symmetry Comparison
Flatworms - Phylum Platyhelminthes
 Simplest
– dorsoventrally
flattened (flat backs &
bellies)
 triploblastic (composed
of three fundamental cell
layers)
 Real organs & organ
systems
 But, no body cavity other
than the gut
Flatworms
Phylum Platyhelminthes
Central nervous system =
simple brain (aggregation of
nerve cells)
 lack an anus; the same
pharyngeal opening both
takes in food and expels
waste
 must respire by diffusion,
and no cell can be too far
from the outside, making a
flattened shape necessary
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Platyhelminthes
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Life without a coelom : The image at left is a fluke
(possibly a species of Probolitrema). Flukes, like
other parasitic flatworms, have complex life cycles
often involving two or more host organisms. At right,
a planarian (Dugesia). Planarians are free-living
flatworms, and have a much simpler life history. They
inhabit freshwater, and are carnivores (even without
teeth) or scavengers. Most are less than a centimeter
long.
Marine Flatworms
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Marine flatworms : The marine flatworms (polycladids) are the
largest of the free-living flatworms, sometimes reaching lengths of
15 centimeters. Polycladids get their name from their highly
branched digestive cavity. These individuals were photographed on
a reef near the island of Guam.
3 Groups of Flatworms
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1. Class Turbellariafree-living, include the
planarian, Dugesia,
found in the oceans,
fresh water, & in
moist terrestrial
habitats, a few are
parasitic
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2. Class Trematoda, or flukes, all parasitic, have complex life cycles
specialized for parasitism in animal tissues. Members of one major taxon of
flukes, the Digenea -- which includes the human lung fluke -- pass through
a number of juvenile stages that are parasitic in one, two, or more
intermediate hosts before reaching adulthood, at which time they
parasitize a definitive host.
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Flatworms include non-parasitic worms such as planaria, which live in water, and parasitic
flukes and tapeworms. The human liver fluke infects over 75% of the people in parts of Japan,
China, and South Asia. The adult fluke, about 3/4 inch long, lives in the bile ducts of the liver;
its eggs (1) pass from the body in the feces. The eggs, containing larvae, are eaten by water
snails (2) and then develop into another form, which passes into the water. They then bore into
the bodies of fishes (3). When raw fish is eaten (4) - as is common in the Orient - the young
worms swim from the intestine into the fine branches of the bile duct and grow to maturity.
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3. Class Cestoda, or
tapeworms, are
intestinal parasites in
vertebrates, and they
also show anatomical
& life history
modifications for
parasitism.
Use suckers or hooks
to latch on
50 ft worm found in
Sperm Whale
Beef Tapeworm - The cestodes (tapeworms) Taenia saginata (beef
tapeworm) and T. solium (pork tapeworm). Taenia solium can also
cause cysticercosis. Life Cycle:
Ribbon Worms
Phylum Nemertea
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about 900 known species
the European nemertine Lineus longissimus has been known to
reach 30 meters (nearly 100 ft) in length,
Most nemertines are marine
Proboscis-wraps around the prey, and toxic secretions immobilize
the prey
Stylet-piercing barb
nemertines are carnivorous; most feed on small invertebrates like
crustaceans and annelids, but some feed on the eggs of other
invertebrates, and a few live inside the mantle cavity of molluscs
and feed on microbes filtered out by the host.
nemertines have major features that flatworms lack, notably a
complete gut with an anus, and a system of blood vessels. This
vessel system may in fact be homologous with the coelom, or
fluid-filled lined body cavity
True organsw/ organ system & central nervous system
Proboscis
 Prostoma
rubrum, an
example of the
phylum
Nemertea, with
its long proboscis
everted.
Nematodes - Roundworms
Phylum Nematoda
Nematodes are the most numerous multicellular animals on
earth
 Most common in soil & marine sediments
 nearly 20,000 described species (>500,000 total)
 1,000 somatic cells
 possess digestive, nervous, excretory, and reproductive
systems, but lack a discrete circulatory or respiratory system
 range from 0.3 mm to over 8 meters
 The largest nematode ever observed is Placentonema
gigantisma, discovered in the placenta of a sperm whale w/ 32
ovaries
 Found inhabit intestines of seals & dolphins & flesh of fish
(sashimi)
 Humans - hookworm, trichinosis and elephantiasis
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Intestinal Roundworms, of which Ascaris is
a common form, infect wild and domestic
animals and man. Eggs drop to the ground in
animal feces. Humans are infected by eating
contaminated food. The diagram at right shows
the life history of Ascaris. Eggs hatch into
larvae in the intestinal tract and bore through
intestine wall (1). Blood carries larvae to lungs
(2), where they grow. They are then coughed
up or crawl up windpipe to back of mouth (3),
are swallowed (4), and mature in intestine (5).
A female worm living in the intestine may have
millions of eggs in its body. These pass out in
feces (6) and, if eaten by other animals, start
the life cycle over again.
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Hookworm, once a serious disease in the
southern U.S., is still common in the warm
areas of the world. Infected people lack
energy. The hook-worm life cycle is like that
of intestinal roundworms except that
infection occurs as larvae hatched in the
warm soil bore through the skin, usually on
the soles of the feet, to enter the blood.
Trichina Worm
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Round Worm
The trichina worm lives inside the
small intestine of a host animal,
where it mates and reproduces.
Once her eggs have been
fertilized, the female burrows into
the intestinal wall and releases her
larvae. The larvae migrate into the
lymph channels of the intestine,
from which they enter the
bloodstream and travel to all parts
of the body. When the larvae
reach the skeletal muscles they
burrow into the muscles and form
tough cyst-like cocoons. The host
secretes lime salts, which are
deposited in the capsule,
eventually transforming the
capsule into a completely calcified
cyst. The worms may live in the
cyst for years until they are
consumed and digested by another
mammal.
Nematode Worms
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Marine Nematode - Draconema
Nematode Worms
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Elephantiasis Nematode
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Wucheria bancrofti
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Here Parborlasia corrugatus
worms are eating fish eggs. P.
corrugatus has a one-way gut
with a large mouth and a closed
circulatory system; nemertean
worms are the simplest animals
with a circulatory system. Like
other proboscis or nemertean
worms, the wedge-shaped head
of P. corrugatus has a fluid-filled
cavity used to rapidly shoot a
barbed proboscis which the
worm uses to capture prey and
defend itself [1]. This harpoonlike proboscis has adhesive
secretions which secure prey. P.
corrugatus is chemically
defended by an acidic mucus
(pH 3.5) which potential
predators avoid [4].
Segmented Worms
Phylum Annelida
Everybody's favorite, worms. . .
earthworms, leeches,
polychaetes
 about 9000 known
species
 Segmentation
 Hydrostatic Skeleton
 Coelom
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Polychaete Worms
Class Polychaeta
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Mostly marine- 10,000
species
2-4 in.
Proboscis w/ jaws
Parapodia – flattened
extensions
Setae – bristles (Fig. 7.15)
Closed Circulatory System
Gills w/ capilaries on
parapodia & body allow
respiratory exchange
Polychaete External Anatomy
Nereis species
Clam or Sand Worm
More Annelids
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Class Oligochaetes
– small, live in
mud/sand
Marine relative of
earthworms
Lack parapodia
And More Polychaetes
Leeches (Class
Hirudinea) – mostly
FW, marine species
are found attached
to fish & inverts
(parasitize)
 Sucker at each end
w/ no parapodia
 hermaphroditic
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Phylum Pogonophora
Beard Worms
(pogonophorans) –
lack a mouth and
gut– use symbiotic
bacteria to
manufacture food.
 4in.-7ft. – Read
Vestimentiferans –
hydrothermal vent
worms
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Leeches in the eye of an unfortunate soul who drank from
the wrong pond in India. Probably Hirudinaria granulosa.
- Mark E. Siddall
Peanut Worms
Phylum Sipuncula
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Soft, unsegmented
bodies (fig. 7.18,
p.124)
320 known species
.4in.-14in.
Deposit feeders
Peanut shaped
Echiurans
Phylum Echiura
Marine
 Look like soft
unsegmented
sausages buried in
mud/sand
 Spoon-like or
forked proboscis
 Deposit feeders
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