How do the acoelomates fit in? Porifera unknown common ancestor Cnidaria triploblastic organ level...
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![Page 1: How do the acoelomates fit in? Porifera unknown common ancestor Cnidaria triploblastic organ level of organization Platyhelminthes protonephridia cephalization.](https://reader036.fdocuments.in/reader036/viewer/2022062409/5697bfc61a28abf838ca7349/html5/thumbnails/1.jpg)
How do the acoelomates fit in?
Porifera
unknown common ancestor
Cnidaria
triploblastic
organ level of organization
Platyhelminthes
protonephridia
cephalization
Ladder-like nervous system
Nemertea
proboscis
Complete digestive system
Closed circ. systemacoelomate
acoelomate
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How do the Pseudocoelomates fit in?
unknown common ancestor
Porifera
Cnidaria
Platyhelminthes Nemertea
the pseudocoelomates
NematodaRotifera
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Pseudocoelomates
There are 9 different phyla that are classified as pseudocoelomates.
We are only covering 2 phyla:
Nematoda Rotifera
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Pseudocoelomate Characteristics
Organ level of organization
Tissues are organized to for 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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Pseudocoelomate Characteristics
“false” body cavityectodermectoderm
mesoderm
endoderm
Gut
pseudocoelom
the pseudocoelom is lined by mesoderm on ONE side only
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Pseudocoelomate Characteristics
the pseudocoelomectoderm
• 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
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Pseudocoelomate Characteristics
• with anterior and posterior ends
Bilateral Symmetry
Cephalization
• concentration of sensory organs in the head of the animal
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Pseudocoelomate 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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Pseudocoelomate Characteristics
• each individual of a species has the same # of cells
• growth occurs by cells getting bigger rather than dividing
Eutely
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Phylum Nematoda
the roundworms
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Physiology
Life Style– Free-living– parasitic
Digestion– complete system (have an anus)– some regional specialization (e.g.
an esophagus)
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PhysiologySkeletal 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
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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
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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
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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
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Physiology
Reproduction
Sexual– usually dioecious– often the sexes are sexually dimorphic – internal fertilization– males have ameboid sperm
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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
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Ecology
• Many nematodes are important parasites of both plants and animals.
parasite of soybean plants
parasite of tomato plants
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Parasites
Eye worm (Loa loa):• transmitted by fly bites• larvae go through bloodstream • adults live in subcutaneous tissue
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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
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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
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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
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ParasitesTrichinella spiralis:• causes Trichinosis• transmitted by eating undercooked pork• juveniles encyst within host muscle cells
juvenile
Host muscle cell
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Ecology
• The study of the model nematode C. elegans has resulted in important discoveries in genetics and development.
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Phylum Rotiferathe rotifers
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The “wheel” animals
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Physiology
Feeding– have a “crown” of cilia called a
corona – the corona creates a
current to bring food into the mouth
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Physiology
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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PhysiologySome of the trophi (jaws):
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Physiology
Life Style– Free-living
Digestion– complete system (have an anus)– some regional specialization (e.g.
mastax-trophi complex)
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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
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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)
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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)
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Physiology
• 2 types of eggs: amictic & mictic
Amictic eggs
• diploid (mitotically produced)• can’t be fertilized• develop into diploid, amictic females
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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
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• 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!
Ecology
![Page 39: How do the acoelomates fit in? Porifera unknown common ancestor Cnidaria triploblastic organ level of organization Platyhelminthes protonephridia cephalization.](https://reader036.fdocuments.in/reader036/viewer/2022062409/5697bfc61a28abf838ca7349/html5/thumbnails/39.jpg)
Here are some of the other pseudocoelomate phyla
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Loricifera
Priapulida
Kinorhyncha
Nematomorpha
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Acanthocephala
Entoprocta
Gastrotricha
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How do the Pseudocoelomates fit in?
unknown common ancestor
Porifera
Cnidaria
Platyhelminthes Nemertea
Nematoda Rotifera
triploblasticorgan level of organization
mastax-trophicorona
pseudocoelomno cilia
longitudinal muscles only
complete digestive system