Download Lecture 15 - Matthew Bolek

Gnathiferans and Smaller
Lophotrochozoans
• Chapter 9
Protostomes Characteristics
• Protostome groups consisting of two large
clades the Lophotrochozoans and the
Ecdysozoans.
• Lophotrochozoans include 10 smaller
protostome phyla.
• Acoelomate, Pseudocoelomate or Eucoelomate
bodies.
Protostome Characteristics
Protostome
Development is characterized by:
• blastopore becomes the mouth
• Spiral / determinate cleavage
• Schizocoely
Mouth Formation
Blastopore becomes the mouth and the anus
forms secondarily
Future anus
blastopore
archenteron
(primitive gut)
mouth
Cleavage
• Cleavage is the initial process of
development after fertilization of the egg.
Radial Cleavage planes are
symmetrical to the polar axis
Produces regulative development
Spiral Cleavage: cleavage planes are
oblique to the polar axis
Produces mosaic development
Schizocoely
blastocoel
Mesodermal cells
Split in mesoderm
ectoderm
endoderm
Developing coelom
mesoderm
Body Cavities in Triploblastic
Animals
Acoelomate Characteristics
No body cavity
ectoderm
mesoderm
Gut
endoderm
Pseudocoelomate Characteristics
“false” body cavity
ectoderm
pseudocoelom
mesoderm
Gut
endoderm
the pseudocoelom is lined by mesoderm
on ONE side only
Eucoelomate (Coelomate) Characteristics
Have a “true” body cavity that is completely surrounded
by mesoderm
ectoderm
coelom
mesoderm
Gut
endoderm
Coelomate or Eucoelomate
Characteristics
the coelom
• is a closed, fluid filled cavity that surrounds
the gut
•mesodermal membranes (mesenteries)
suspend organs in the coelom
The Lophotrochozoa
Lophotrochozoans Characteristics
Organ level of organization
Tissues are organized to form organs which are used
to accomplish physiological functions.
Triploblastic
3 Germ Layers
3 Tissue Layers
endoderm
gastrodermis
mesoderm
mesoderm
ectoderm
epidermis
Lophotrochozoans Characteristics
Bilateral Symmetry
• with anterior and posterior ends
Cephalization
• concentration of sensory organs in
the head of the animal
Lophotrochozoans Characteristics
Digestive System
• complete (they have an anus!)
• some regional specialization
Circulation System
• no system (or organs)
• performed by the pseudocoelom fluid
Gnathifera
There are 4 different phyla that are classified as
Gnathifera.
Rotifera
Acanthocephala
Gnathostomulid
Micrognathozoa
Gnathifera Characteristics
• Other than the Acanthocephalans all phyla
posses small, cuticular jaws with a
homologous microstructure.
Gnathifera Characteristics
Eutely
• each individual of a species has the same
number of cells
• growth occurs by cells getting bigger rather
than dividing
P: Gnathostomulida : gnatho,
“jaw”; stoma, “mouth”
•
•
•
•
•
•
Benthic, interstitial
Monociliated epidermal cells
Jaws and muscular pharynx
Often vermiform
Hermaphroditic
About 80 species have been described
jaws and
basal plate
Gnathostomulid
P: Micrognathozoa
Limnognathia maerski
Phylum Rotifera
the rotifers
Phylum Rotifera: rota, “wheel”; fera,
“to bear”
• Includes about 1,800 described species.
• Tiny metazoans (up to 3 mm), that are
predominantly freshwater although some
are marine and terrestrial (live in
mosses).
The “wheel” animals
{
Head
Trunk
Foot
{
{
Corona
– have a “crown” of cilia called a corona
– the corona creates a
current to bring food into
the mouth
Corona of Foscularia species
Body Wall and Support
• Most rotifers possess a gelatinous
cuticle outside the syncytial
epidermis.
• They possess a skeletal lamina
which produces the lorica and
other surface structures.
Rotifers of the genus Keratella don't possess a foot. They are fast
swimmers. Their lorica (shell) looks like a jigsaw puzzle and is
covered with small spikes. There are long spines on each corner.
The photograph shows how the cilia are grouped in tufts.
Kellicottia is a rotifer that lives in open waters like
lakes. The long spines might prevent them from being
eaten by predators.
Well developed and
complex muscle
bands
Body appears to be
composed of segments, they
are superficial segments.
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….
Mastax-trophi complex
Some of the trophi (jaws):
Ramate mastax
These are crushing/grinding forms.
Malleate mastax
Some of the trophi (jaws):
Forcipate mastax
These are grasping, predatory forms.
Incudate mastax
Nervous and sensory system
- cephalization, cerebral ganglia
- dorsal and ventral nerve cords
- eyes
Circulatory system
– no system (no organs)
– performed by fluid in pseudocoelom
Excretion
– protonephridia and flame cells
– cloacal bladder (collects wastes)
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)
Reproduction
• 2 types of eggs: amictic & mictic
Amictic eggs – Asexual Reproduction
• diploid (mitotically produced)
• can’t be fertilized
• develop into diploid, amictic females
Reproduction
Mictic eggs- Sexual and Asexual Reproduction
•
•
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
Resting eggs of
monogonot
rotifers
Reproduction
• 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!