Transcript Major Divisions of Life - FSU Biology

How do the acoelomates fit in?
Nemertea
Platyhelminthes
acoelomate
Complete digestive system
acoelomate
Cnidaria
Porifera
Closed circ. system
Ladder-like
nervous
system
proboscis
cephalization
protonephridia
organ level of organization
triploblastic
unknown
common ancestor
How do the
Pseudocoelomates fit in?
Nematoda
the pseudocoelomates
Platyhelminthes
Cnidaria
Porifera
unknown
common ancestor
Nemertea
Rotifera
Pseudocoelomates
There are 9 different phyla that are classified
as pseudocoelomates.
We are only covering 2 phyla:
Nematoda
Rotifera
Pseudocoelomate
Characteristics
Organ level of organization
Tissues are organized to for organs which are
used to accomplish physiological functions
Triploblastic
3 Germ Layers
3 Tissue Layers
endoderm
gastrodermis
mesoderm
mesoderm
ectoderm
epidermis
Pseudocoelomate
Characteristics
“false” body cavity
ectoderm
ectoderm
pseudocoelom
mesoderm
Gut
endoderm
the pseudocoelom is lined by mesoderm
on ONE side only
Pseudocoelomate
Characteristics
the pseudocoelom
ectoderm
• is a closed, fluid filled cavity
• contains digestive, excretory, and
reproductive structures
• the fluid within acts as a circulatory
system
• the fluid within acts as a hydrostatic
skeleton against which the muscles work
Pseudocoelomate
Characteristics
Bilateral Symmetry
• with anterior and posterior ends
Cephalization
• concentration of sensory
organs in the head of the animal
Pseudocoelomate
Characteristics
Digestive System
• complete (they have an anus!)
• some regional specialization
Circulation System
• no system (or organs)
• performed by the pseudocoelom fluid
Pseudocoelomate
Characteristics
Eutely
• each individual of a species has the
same # of cells
• growth occurs by cells getting bigger
rather than dividing
Phylum Nematoda
the roundworms
Physiology
Life Style
– Free-living
– parasitic
Digestion
– complete system (have an anus)
– some regional specialization (e.g.
an esophagus)
Physiology
Skeletal system
- fluid in pseudocoelom acts as a
hydrostatic skeleton
Cuticle
– covers body (secreted by epidermis
+ composed mostly of collagen)
– functions as a primitive external
skeleton
Physiology
Movement
– longitudinal muscles ONLY
(results in “whiplike” motion)
– No external/internal cilia
 even sperm don’t have flagella
http://www.devgen.com/devpage/largeimage/wild.html
Physiology
Nervous system
- cephalization, cerebral ganglia
- dorsal and ventral nerve cords
Circulatory system
– No system (no organs)
– performed by fluid in pseudocoelom
Excretion
– Renette glands
Physiology
Reproduction
Sexual
– usually dioecious
– often the sexes are sexually dimorphic
(males and females look different)
Males often have a spicule
at the end of their tail used to
insert their sperm into the female
Physiology
Reproduction
Sexual
– usually dioecious
– often the sexes are sexually dimorphic
– internal fertilization
– males have ameboid sperm
Ecology
• There are >12,000 species that are found in almost
all habitats (marine, freshwater, underground, inside
plants and animals, etc…).
• They are also incredibly abundant. For example:
• a m² of soil may contain >4 million nematodes
• a decomposing apple may contain >90,000
nematodes of a single species
Ecology
• Many nematodes are important parasites of both
plants and animals.
parasite of
soybean plants
parasite of
tomato plants
Parasites
Eye worm (Loa loa):
• transmitted by fly bites
• larvae go through bloodstream
• adults live in subcutaneous tissue
Parasites
Intestinal roundworm (Ascaris):
• transmitted by contaminated food
• adults live in small intestine
• it’s estimated that 20% of world’s population is
infected (~1.3 billion people)
this intestine was completely blocked
Parasites
Guinea worm (Dracunculus medinensis):
• transmitted by infected copepods in drinking water
• larvae move into the body cavity
• female adult migrates to the subcutaneous tissue, causes an
ulcer/blister, and releases eggs through hole when host comes in
contact with water
Parasites
Guinea worm (Dracunculus medinensis):
• traditionally removed by winding the worm around
a matchstick over the course of several days
• this may be the basis for the Caduceus symbol
used in the medical field
Parasites
Trichinella spiralis:
• causes Trichinosis
• transmitted by eating undercooked pork
• juveniles encyst within host muscle cells
juvenile
Host
muscle cell
Parasites
Heartworms (Dinofilaria immitis):
Ecology
• The study of the model nematode C. elegans has
resulted in important discoveries in genetics and
development.
Phylum Rotifera
the rotifers
The “wheel” animals
Physiology
Feeding
– have a “crown” of cilia called a
corona
– the corona creates a
current to bring food into
the mouth
Physiology
Feeding
– have a specialized feeding structure
called the:
mastax-trophi complex
modified jaws
within the mastax
a modified
muscular pharynx
Looking down into the
corona….
Physiology
Some of the trophi (jaws):
Physiology
Life Style
– Free-living
Digestion
– complete system (have an anus)
– some regional specialization (e.g.
mastax-trophi complex)
Physiology
Skeletal system
- fluid in pseudocoelom acts as a
hydrostatic skeleton
Movement
– the corona
– pedal glands (produce adhesive),
as well as foot and toe (spurs) for
attachment to substrate
Physiology
Nervous system
- cephalization, cerebral ganglia
- dorsal and ventral nerve cords
Circulatory system
– no system (no organs)
– performed by fluid in pseudocoelom
Excretion
– protonephridia and flame cells
– cloacal bladder (collects wastes)
Physiology
Reproduction
Sexual
- complex life cycle with different types of
eggs
- usually dioecious but in some groups,
males are absent (parthenogenesis)
- Parthenogenesis:
unisexual reproduction where females produce
offspring from unfertilized eggs (virgin birth)
Physiology
• 2 types of eggs: amictic & mictic
Amictic eggs
• diploid (mitotically produced)
• can’t be fertilized
• develop into diploid, amictic females
Physiology
Mictic eggs
•
•
haploid (meiotically produced)
produced after some sort of environmental
stimulus (eg. high density, change in temperature)
 if unfertilized, develop into haploid males
 if fertilized, secrete a thick, protective shell
until the environment is favorable again, after
which they develop into diploid, amictic
females
Ecology
• There are ~1500 species. Although they are found
mainly in freshwater habitats, there are a few marine
rotifer species and a couple of species are even
found in mosses!
• Because of the reduced role of males in
reproduction, most males are incapable of feeding
and do not even have a digestive tract (they are just
there for sperm delivery!).
• Males have never been recorded in Bdelloid rotifers.
This means they haven’t had sex in millions of years!
Here are some of the other
pseudocoelomate phyla
Loricifera
Nematomorpha
Kinorhyncha
Priapulida
Acanthocephala
Gastrotricha
Entoprocta
How do the
Pseudocoelomates fit in?
Nematoda
Rotifera
mastax-trophi
corona
no cilia
longitudinal muscles only
Platyhelminthes
Nemertea
Cnidaria
Porifera
complete
digestive system
organ level of organization
triploblastic
unknown
common ancestor