The Lophotrochozoa. Protostomes Characteristics Protostome groups consisting of two large clades the...
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Transcript of The Lophotrochozoa. Protostomes Characteristics Protostome groups consisting of two large clades the...
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The Lophotrochozoa
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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.
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Protostome Characteristics
Protostome
Development is characterized by:
• blastopore becomes the mouth
• Spiral / determinate cleavage• Schizocoely
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Mouth Formation
blastopore archenteron(primitive gut)
Future anus
mouth
Blastopore becomes the mouth and the anus forms secondarily
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Cleavage
• Cleavage is the initial process of development after fertilization of the egg.
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Radial Cleavage planes are symmetrical to the polar axis
Produces regulative development
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Spiral Cleavage: cleavage planes are oblique to the polar axis
Produces mosaic development
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Schizocoely
ectoderm mesodermendoderm
Split in mesoderm Developing coelom
Mesodermal cells
blastocoel
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Lophotrochozoans Characteristics
The name Lophotorochozoa comes from the names of the larval type of the two major animal groups including the Lophophorata and the Torchozoa.
Trochophore Larva
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Lophotrochozoans Characteristics
Organ level of organization
Tissues are organized to form organs which are used to accomplish physiological functions.
Triploblastic
3 Germ Layers
endoderm
mesoderm
ectoderm
3 Tissue Layers
gastrodermis
mesoderm
epidermis
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Lophotrochozoans Characteristics
• with anterior and posterior ends
Bilateral Symmetry
Cephalization
• concentration of sensory organs in the head of the animal
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Lophotrochozoans Characteristics
• complete (they have an anus!)• some regional specialization
Digestive System
Circulation System
• no system (or organs)• performed by the pseudocoelom fluid
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Gnathiferans and Smaller Lophotrochozoans
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The Lophotrochozoa
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Gnathifera
There are 4 different phyla that are classified as Gnathifera.
Rotifera
Acanthocephala
Gnathostomulid
Micrognathozoa
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Gnathifera Characteristics
• Other than the Acanthocephalans all phyla posses small, cuticular jaws with a homologous microstructure.
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Gnathifera Characteristics
• each individual of a species has the same number of cells
• growth occurs by cells getting bigger rather than dividing
Eutely
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P: Gnathostomulida : gnatho, “jaw”; stoma, “mouth”
Gnathostomulid
jaws andbasal plate
• Benthic, interstitial
• Monociliated epidermal cells
• Jaws and muscular pharynx
• Often vermiform
• Hermaphroditic
• About 80 species have been described
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P: MicrognathozoaLimnognathia maerski
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Phylum Rotiferathe rotifers
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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).
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The “wheel” animals
{{
Head{Trunk
Foot
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Corona– have a “crown” of cilia called a corona – the corona creates a
current to bring food into the mouth
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Corona of Foscularia species
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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.
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Rotifers of the genus Keratella donot 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.
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Kellicottia is a rotifer that lives in open waters of lakes. The long spines might prevent them from being eaten by predators.
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Well developed and complex muscle bands
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Body appears to be composed of segments, they are superficial segments.
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Feeding– have a specialized feeding structure called
the:
mastax-trophi complex
a modified muscular pharynx
modified jaws
within the mastax
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Looking down into the corona….
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Mastax-trophi complex
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Some of the trophi (jaws):
Ramate mastax Malleate mastax
These are crushing/grinding forms.
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Some of the trophi (jaws):
Forcipate mastax Incudate mastax
These are grasping, predatory forms.
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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)
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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
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Reproduction
• 2 types of eggs: amictic & mictic
Amictic eggs – Asexual Reproduction
• diploid (mitotically produced)• can’t be fertilized• develop into diploid, amictic females
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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
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Brachionus is a very common genus. They carry their eggs on their foot. The various species can be identified by the spines on their lorica (shell).
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Asplanchna is a large bag-shaped rotifer. This individual carries an almost fully developed embryo inside.
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Eggs maintained in maternal tube
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Resting eggs of monogonont rotifers
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• 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!
Reproduction