How different Invertabrates move
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| As you work your way up the tree, locomotion gets more complex. The paragraphs below explain the different animal movements in each phylum. |
Arthropoda
Arthropods have jointed appendages that they use to sense, walk, feed and mate. They can do this by flexing one body segment after the other (relaxation and contraction of striated muscle fibres). The appendages can be either biramous (branches into two and each branch has a series of segments attached end to end) or uniramous (single series of segments attached end to end).Some examples are crabs, insects, lice, shrimp, spiders and scorpions.
The following photos show how in the phylum Arthropodia, jointed appendages are very complex and they help the organism do many different thing
MolluscaThe under side of Mollusks consists of a muscular foot which can do different things in different classes. It contains statocysts (balance sensors), it can secrete mucus (lubricant), the foot can suction, it can burrow and it is capable of jet propulsion. Some examples are snails, slugs, octopus, oysters, and squids.
Annelida
There are many ways that annelids move. Some move by peristalsis (waves of contraction and expansion as shown in the video below) and some move by parapodia (kind of like pseudopods). Septa, which separtate body segments, enable the muscles to change the shape of induvidual segements. Other annelids move by whipping movements or cilia. Some examples are earthworms and leeches.
Peristalsis
Nematodes use a whip-like wriggle to swim. This is callled undulatory propulsion with sinusoidal waves (repetitive oscillation). Some examples are hookworms, pinworms and whipworms.
A movie: Nematoda Locomotion
Echinodermata
http://www.mbgnet.net/salt/animals/echinod.htm
All echinoderms have thousands of tiny tube feet or podia on and many have suction cups on the end. The tube feet are filled with water, and when the organism wants to attach to a surface the water is sucked from the feet. When the organism wants to release it just fills up the feet with water. This is the vascular system. Some examples are sea stars, sea cucumbers and sea urchins.
Platyhelminthes
Platyhelminthes are unsegmented so they have special ways of moving. One way is by using layers of muscles. Another way is by gliding along a slime trail using cilia. An example is a water planaria, as shown below.
Cnideria
http://www.infoplease.com/dk/encyclopedia/cnidarians.html
Some move by contracting their hollow bodies to propel forward (jellyfish). While others move by using tentacles or cilia (hydra).
Some move by contracting their hollow bodies to propel forward (jellyfish). While others move by using tentacles or cilia (hydra).
Porifera
Adult poriferans are sessile which means they dont move yet immature poriferans (larvae) do move. An example is a sponge.
Embryology
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| The zygote farthest to the right is undergoing Gastulation and the one next to it is undergoing the formation of a blastula. You can see these steps more clearly in the diagram below. |
Blastula Formation
- After many daughter cells are made they secrete and surround a fluid. The fluid is the blastocoel and the layer of surrounding cells are the blastula.
Gastrulation
- A second layer of cells forms by invagination (half of the first layer turns itself inside out and creates an opening called the blastopore).
- Another opening is made, forming the digestive tract between it and the blastopore.
- Steps after this distinguish the difference between protostomes and deuterostomes.
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| An example of blastula formation, gastrulation and also radial cleavage |
Difference between protostomes and deuterostomes
- Protostomes (mollusks, annelids and arthropods) develop by spiral cleavage (shown below and above) and the first opening is the mouth (blastopore).
- Deuterostomes (echinoderms and chordates) develop by radial cleavage (shown below) and the first opening (blastopore) is the anus.
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