Phylum Aschelminthes

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Phylum Aschelminthes

• Lecture 9
• Invertebrate Zoology

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Aschelminths (or as-can helminths)

• Are a group composed of several phyla which share
  similar characters but are also unfortunately
  many different characters as well not at all
  clear how these phyla are phylogenetically
  related.

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Similar characteristics (in general shared by
all)
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Similar characteristics cont.
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Eleven phyla represented in this group
Nemata (Nematoda) round worms Nematomorphorh
a Horse hair worms Gastrotricha Rotifera
Tardigrada
Acanthocephala Entoprocta Loricifera
(recently described in 1995) Cycliophora Pri
apula (spiny-headed worm)
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Features which vary between groups

• -  Presence or absence of cilia absence in
  Nematoda
• -  Disposition of cuticle internal in Rotifers
• -         Pseudocoloem absent in Gastrotrichs
  (or any body cavity)
• -         Presence or absence of digestive
  tract, (reduced in Nematomorphora)
  
  (absent in Acanthocephala)
• Protonephrida absent or present present in
  rotifers, absent in Nematodes
• - All this variation makes it difficult to unit
  groups!

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Phenomenon of variation
Difference represents divergence from common
ancestor or characters that are similar result of
convergence of characters but had different
phylogenetic histories. Closest
relationships 1)      Gastrotrichs/Nematodes/Nema
tomorphes all have similar developmental
patterns, pharynx, nervous system,
cuticle 2)      Rotifers and Acanthocephala -
both lack cuticle, syncytial epidermis supported
by web of cytoplasmic fibers with permanent
evaginations secretory in rotifers, absorptive
in Acanthocephala.
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Phylum Nemata (Nematoda)

• -Nematodes exhibit eutely cell division stops
  at hatching, all subsequent growth to enlargement
  of cells rather than multiplication of cells.
• -Another trait is known as anhydrobiosis the
  ability to resist long periods of dissication,
  reduced metabolic rates with prolonged state
  inactive state.

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Examples of important nematodes
1) Trichinella encystes in muscle tissue, adult
lives in small intestine. Larvae pass into the
lymphatic system goes to blood stream, organs
and muscles. Passed in next host if tissues
eaten. Generally fatal in humans. 2) Ascaris
hosts are pig and humans. 3) Ancylostoma
hookworm, eggs in feces, hatch, larvae invade
tissues similar to trematode cercariae
migrate to lungs via blood stream climb out of
lungs into intestine.
Ancylostoma
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Important Nematodes
4) Wuchereria bancrofti Elephantiasis adult
worms in lymph glands, produce microfilariae
larvae found in blood migrate into blood,
rhythmically timed with occurrence of mosquito
activity (similar to malaria), next host mosquito
host results in chronic infection of lymph nodes,
leads to blockage with scar tissue. Fluid builds
up and swells appendages
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C. elegans
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Major organ systems of nematodes
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General morphology of nematodes
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Phylum Nematomorpha
-Very interesting phylum. Well developed cuticle
without functional cilia or flagella. Only
longitudinal muscles. They also have unique
larvae that are parasitic in arthropods. It also
is without special excretory, circulatory or gas
structures. Occurs in all aquatic environments.
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Nematomorpha general Characteristics
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Phylum Rotifera
-Possess unique pharynx modified as a mastax,
containing jawlike elements called trophi
Posterior end bears toes and adhesive glands.
Parthogenesis common. -With a unique
retrocerebral organ. Flexiblity in developmental
polymorphism reflected in environmental
conditions. Most species are only 2-3 mm in size.
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Rotifera general characteristics
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Phylum Gastrotricha
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Gastrotricha anatomy
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• Review of Aschelminths
•  
• Similar Characteristics (in general shared by
  all)
•  
• Pseudocoelom fluid-filled cavity, thought to be
  persistence of
• embyronic blastocoel but recently refuted.
• Cavity however is not lined with a peritoneum
  not coelomate.
• possesses cuticle noncellular layer, generally
  overlying epidermis
•  
• protonephridia absent or present present in
  rotifers, absence in
• Nematodes
•  
• Lots of variation 
•  

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•  
• Exhibits fixed cell numbers (Eutely)
•  
• Tissues tend to be syncytial (lack cell
  membranes)
•  
• Specialized pharynx muscularized
•  
• Absence of respiratory/circulatory systems
• Protonephridia occur in rotifers with flame
  cells
• - similar to flat worms.

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Some interesting observations     Nematodes
exhibit eutely, cell division stops, all
subsequent growth due to enlargement of cells
rather than multiplication of cells.     Anhydrobi
osis ability to resist long periods of
dessication, reduced metabolic rates lead to
inactive stage able to survive harsh
conditions. Possess a hydrostatic skeleton
high internal pressure is maintained within the
fluid- filled pseudocoel gives rigidity to the
body. Presence of osmoregulatory organs - Gland
cells referred to as renette protonephrida are
absent but a tube is present w/midventral pore
for exiting waste.
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Examples of important nematodes   Trichinella
enystes in muscles, adult lives in small
intestine larvae pass into lymphatic system
to blood stream, organs and muscles, Passed
into next host if tissues are eaten generally
fatal in humans.   Ascaris pigs and
humans   Ancyostoma hook worm, here eggs in
feces, hatch larvae tissues (similar to
trematoda cercariae ) migrate to longs via
bloodstream, climb into intestine
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Bauplan of Kinorynch
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Rotifera - Basic body plan divived into 3
parts   Head, bearing cilia called Corona
surrounds the mouth with cilia, trochus beats
metachronal fashion illusion of revolving
circle.   Named wheel-bearer Functions
1) generate feeding currents 2)
locomotion   Second segment trunk, cylindrical
or flattened, covered /cuticle within the
epidermis, (intracellular skeleton). This
overlying casing called the Lorica.   Third
segment, body ends in foot and associated pedal
glands.  
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Rotifer
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Bauplan of Rotifer
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Bauplan of Gastrotrich
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Digestive system mouth passes into pharynx
or mastax The mastex is a muscular chamber
containing a set of jaws called trophy this
structure is used in taxonomy. The jaws have
two sections a ramus and fulcrum. This
structure functions in grasping, grinding or even
sucking acts as a pump.
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Adaptations 1) Parthenogenesis - 2N female
---- 2N eggs (environment stable)   2N
female ---- 1N eggs (environment
deteriorating) 2) Anhydrobiosis
nearly complete dessication. Withstand
conditions for about 100 years add water,
instant rotifers! 3) Can
withstand extremes up to 151o C down to 272o
C!! 4)
Cyclomorphosis- changes in structure of cuticle
in response to predators
 
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Phylum Nematoda - largest group of
non-segmented worms. - Size 80 um to 9 m
(worms in placenta of sperm whales) - occur
everywhere - most widespread and abundant
invertebrate besides insects.   - Many are
parasitic both plant and animals. One study
found 9 billion nematodes/acre of Iowa farm
soil. Estimated ½ million spp. with only
15,000 described.  
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Major organs of Nemertean
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Cross Section of Nemertean
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Reproductive apparatus of Nemertean
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Nemerteans
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Head region of Nemertean
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Cross section of Nemertean
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Very simple tubular structures. The
cuticle - contains layers of scleroproteins   -
often quinone tanning embedded with skeletal
elements rods and fibers with elastic
annulated surface. - Noncellar (syncytial),
composed of collagen (unique to nematodes).
Molt 4 times through development, secreted by
epidermis.
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Phylum Acanthocephala
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Acanthocephalan bauplan
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Parasitic Acanthocephalan life
cycle
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Head of Acanthocephalan
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Phylum Ciliophora - bauplan
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Ciliophora a new group
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Ciliophorids
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Ciliophorid
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Phylum Entoprocta - characteristics
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Entoprocts- bauplan and photos
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Entoproct
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Entoproct
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Entoproct
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Phylum Gnathostomulida-characteristics
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Gnathostomids - bauplan
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Gnathostomulia sp.
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Gnathostomid
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Phylum Loricifera characteristics
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Loriciferans bauplan
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Loriciferans diagram
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Loriciferan
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Phylum Nematomorpha characteristics
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Cross Section of Nematomorph
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Nematomorphid
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Phylum Priapula characteristics
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Priapulids diagram
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Priapulid
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Priapulid drawing