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Animal Phyla |
I was surprised when I saw my first sponge. It looked like a piece of raw liver attached to a rock. It did not react to touching or other stimuli and had no tentacles, arms or anything to capture food or to get rid of wastes. It did not look much like an animal. Sponges have numerous holes which gave the phylum the name which means "pore bearer".
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Cnideria or Coelentrata |
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Cnideria means "nettle" because these animals can sting like the stinging plants called nettles. The most commonly know animal in this phylum are the jelly fish. This term is misleading because it is not related to fish. Corals also belong to this phylum.
The flat worms are the most primitive of all worms. Many have adapted to a parasitic mode of life.
This huge taxon of animals do tremendous economic damage to man. They are vicious parasites to man, other animals and to plants. You saw a nonpathogenic example in lab, the vinegar eel.
Annelida means little ring which refers to the ring-like segments that make up the bodies of these animals. Most of us relate to these worms because of we all know the earthworm.
- Examples
- Unique Features
- Has segments
- closed circulatory system with 5 pairs of hearts.
- Most primitive animals to have this type of system
- locomotion.
- seta
- systems
- excretory
- paired nephridia located each segment
- circulatory
- closed circulatory system with 5 pairs of hearts.
- Most primitive animals to have this type of system
- General Features
- bilateral symmetry
- system
- reproductive
- Usually hermaphroditic
- digestive
- complete
- mouth
- crop
- gizzard
- intestine
- anus
- ventilation
- dermal....through the skin
- nervous
- ventral nerve cord with a series of nerve centers "small brains"
- simple brain...nervous tissue is concentrated in the head region
Mollusca means "soft" is applied to the huge group of animals commonly referred to as the "soft-bodied animals."
Most of us are familiar with this taxon because it contains insects and spiders. Arthropoda means jointed foot/appendage. This is a very successful group of animals.
Echinodermata means "spiny-skinned" animals. These are radially symmetrical headless, brainless, slow-moving marine animals.
The term chordata refers to the rod of cartilage that runs down the back of these animals. This phylum includes all of the animals that are most familiar to us. Chordates are the most complex animals in the world and represent the peak of evolution in the animal kingdom.
APPENDIX
General Information
Evolution of Digestive "food getting and processing"...Systems
Evolution of Circulatory ..."plumbing" Systems.It is important to understand the evolution of methods that organisms to intake nourishment. The most primitive heterotrophic organisms did not utilize any special method for nourishment intake...small organic molecules diffused through the cell membrane. Some protozoan utilized food vacuoles [Images of Food Vacuoles]. Lysosomes were utilized in this type of digestion. The Cnideria have a gastrovascular cavity, but still utilize food vacuoles. Some flatworms have a primitive but with one opening. The first digestive systems with a opening on both ends, the mouth and the anus, were not much more than a tube. But as evolutionary time passed, this tube became specialized with the organs, such as a pharynx, intestines, crop gizzard, stomach, etc. One of the more complex digestive systems that evolved belongs to us.
Over the years several different circulatory systems evolved. Similarly to the other organ system the primitive organisms have the simplest systems. Organism like hydras have no blood distribute substances by diffusion. A circulatory system was not needed in these simple animals. Larger organisms need a specialized system that can transport oxygen and nutrients throughout the organism. Two different types of systems evolved, the open circulatory system and the closed. In the open, blood is pumped through open ended vessels and out among cells. Vertebrates, on the other hand, have a closed circulatory system, or a Cardiovascular system that consists of a branching network throughout the body. This network contains many different vessels that include arteries, capillaries, veins, and many other smaller tube-like streams.
Evolution of Ventilation ..."breathing"... Systems
Primitive organisms do not require a specialized ventilation system. The gases can diffuse into the cell or the moist skin of the organisms. Most worms, even the more complex utilize this type of gas exchange. "Evolution experimented with" Arthropod ventilation systems. Insects utilize breathing tubes called trachea. Insect trachea carry air directly from the outside of the animal to the cells inside and waste gases back out same trachea. Arachnids utilize book lungs Various marine animals utilize gills. Snail breath through lungs. Snail lungs do not have the capacity or efficiency of human lungs.....that is if the human does not smoke.
Evolution of Excretory ......"peeing"....Systems
The high protein diet of many animals cause a problem. In water the amine group forms ammonia which is toxic, even at low concentrations.....it alters the cytosol pH. This has to be eliminated...excreted...from the organism. The single celled and primitive organisms excreted their their skin....that is correct....they peeeeed all over themselves. But a little size caused evolution to "develop" excretory systems. Flatworms have the first true excretory system. Special cells called flame cells are located near the head of the animal. These cells have large flagella in them that wave, creating a low pressure area. The flame cells are connected to the rest of the body by a pair of lateral excretory ducts. Wastes are pulled from body cells into the ducts. Once in the ducts, the wastes move toward the flame cells. Once the wastes get to the flame cells they are released through a dorsal excretory pore.
Planarian Excretory System and One Flame Cell (A).(Note the long cilia ("flame") which move material toward the excretory canal.) [from: http://www.uwinnipeg.ca/~simmons/lb6pg6.htm]
Annelids evolved many pairs of excretory organs called nephridia (scroll down to see the diagram) , a pair for each segment. Mammals possess the most complex excretory system....it has kidneys.
Evolution of the Nervous System
The evolution of the
invertebrate nervous system is already
described. Humans have the most complicated nervous system that is described in
various books and Web sites such as Human Nervous System
Evolution of Vertebrate Nervous System
And you thought you had heard of kinky
sex.........Penis Fencing
Some polyclads [flat worms] display bizarre mating behaviour, in
which two animals attempt to inject sperm into the rival by stabbing them with
an erect penis, whilst simultaneously trying to avoid being stabbed themselves.
This behaviour, commonly termed ‘penis-fencing’ is believed to have evolved
in order to combine the benefits of direct access to eggs via hypodermal
injection, whilst avoiding the disadvantages of energy expensive wound repair
and loss of mate-selection choice [Michiels and Newman, 1998].
Worms and Things
