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evolutionary trends of invertebrates
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Evolutionary Trends of Invertebrates
By Lily and Ali
Digestive System
Humans Vs. Invertebrates
Digestive System
As the digestive systems throughout the invertebrates gets more complex, it is easy to see the similarities between their system and ours. For example, we have similar structures such as our esophagus and their pharynx which serve the same function of transporting food from the mouth to the intestines. We also both have developed a coelum which allows us to have organs that can move and grow. The invertebrates crop and gizzard is like a two part stomach that first stores the food, and then breaks it down so we can use the nutrients. Incomplete digestive systems have a "Bouth" a conjoined anus and mouth while organisms with complete digestive systems, such as humans or arthropoda have a separate anus and mouth. Also, the structure of a radula, is incredibly similiar to the teeth and tongue of a human. They are both essential for eating and serve the purpose for cutting and swallowing food. All these similiar characteristics are due to similiar environmental pressures that makes having these traits very advantageous.
Porifera
Porifera
At the start, simple phylums, such as porifera, don't have a digestive system as they are filter feeders. One reason why this could be is because it lacks a coelum.
Cnidaria and Platyhelminthes
Cnidaria and Platyhelminthes
Cnidaria and platyhelminthes are more complex than porifera as they both have an incomlete digestive system. Both phylums have a "bouth" that serves as an anus and mouth. After food enters through the bouth,it gets broken up by enzymes and distrubted throughout the organism by either diffusion or cells.
Nematoda and Echinodermata
They have a more complex digestive system then the past three phylums as they have a complete digestive system. This complete digestive system means the organism has a seperate butt and mouth.
Nematode and Echinodermata
Arthropda and Annelida
Arthropoda and Annelida
These phylums also have a complete digestive system as well as having a pharynx; which connects the mouth to the intestine, the crop; which is used to store food, and the gizzard; which grinds food so it is digestible.
Mollusca
Mollusca are quite similiar to other phylums such as Nematodes and Annelids, however Mollusks have a radula, which is specific to their phylum. A radula is a rasp-like structure of tiny teeth which is used to scrape particles off of a surface.
Mollusca
Nervous System
Humans vs. Invertebrates
Nervous System
It can be hard to see the similarities between invertebrates and humans when comparing phylums such as Porifera to humans: however as the phylums get more developed, it is easy to see how alike we truly are. We share similarities such as in our nervous system with our sensory nerves that respond to stimuli and our motor neurons that activate muscles and glands. Complex brains such as humans, can be easily compared to the brains of squids which, like ours, has developed to not only perform simple tasks but to be able to use tools and problem solve. As invertebrates and vertebrates split from each other, Over millions of year they have begun to converge, showing similiar advantageous traits such as in their nervous system. When faced with much of the same environmental pressures, the animals have developed bigger brains, and better nervous systems, thus serving them better than the organisms who lack it.
Porifera
Simple phylums do not have any cephalization or nervous system. Organisms that show no symmetry most likely do not have any form of cephalization.
Porifera
Cnidaria and Echinodermata
Cnidaria and Echinodermata
Other phylums, such as Cnidaria, and Echinodermata still lack cephalization but can still have a nervous system. Cnidaria has a mesh of nerves (known as a nerve net) that is centered around the mouth. They also possess sensory eyes that can take in shadows. Echinodermata are very similiar to Cnidaria as they have sensory organs that are not only around their mouth but also at the end of each of their appendages.
Nematoda
Nematodes are unique as these segmented round worms still lack a brain, but do have obvious cephalization as their nerves are all bundled at one end. The bundle of nerves is what later gets developed into a brain in other phylums. Nematodes also possess chemical receptors that can "smell" their prey.
Nematoda
Platyhelminthes and Annelida
These two phylums are most likely some of the first to have a brain, being that their brain is still quite simple. Both organisms have obvious bilateral symmetry, a good sign that they have either a nervous system or a form of cephalization.
In Platyhelminthes the sense organs in the front later connect to a simple brain located at the front or in their head. They also have at least one or more long nerve cords that run along it's body, connecting to the brain.
Annelids also have a simple brain that is connected to a ventral (front) nerve cord. Their brains serve the function for movement, reacting to their environment and feeding.
Platyhelminthes and Annelida
Arthropoda and Mollusca
Mollusca, such as bivalves lack true cephalization, although it can be argued that they are technically "all head". Other Mollusks like octopi and squid have the most complex and developed brains out of the phylums. It has been hypothesized that octopi can be smarter than humans but they aren't due to their short life span, only 5 to 7 years, and their "short-range brain" that works better in bursts than it does over long periods of time.
Other than octopi and squids, arthropoda possess the most complex brain out of the invertebrates. They have a dorsal, or back, brain that connects to their ventral, or front, nerve cord. They also have sensory organs on their antenna, mouth, joints, and leg tips. Most Arthropoda also have two or more eyes.
Arthropoda and Mollusca
Humans vs. Invertebrates
In the beginning phylum's of invertebrates many of them did not have eyes such as porifera and cnidaria. Moving forward looking at more of the invertebrates we can begin to see similarities in between the invertebrate eye and the human eye. Molluscs and humans share the ability to produce images of what they see. Annelids were the first invertebrates to have independent cells that we also see in humans. Arthropods have a lens, transparent cones, pigment cells, and have cells that trigger nerve impulses that humans have as well. Based of off what we have found in invertebrates eyes we see that there are several parallels to the human eye and it is very probable that our eyes evolved from theirs.
The Eye
Platyhelminthes
Platyhelminthes are the first invertebrate that we see with eyes. They have a huge regenerative capacity (are able to repair themselves). They have very simple eyes that allow them to see light and dark, their eye is believed to be similar to the prototype imagined by Charles Darwin.
Platyhelminthes
Annelids
Annelids are the first invertebrates to have photoreceptor cells. They have the ability to see light and dark and they are the beginning of independent cells seen in humans.
Annelids
Molluscs
Molluscs are the first phylum of invertebrates to have sensory cells, in humans we have sensory organs such as our eyes, ears, and noses, these organs allow us to sense what is around us. Molluscs have sensory cells that allowed them to evolve into being able to produce images with the light and things they see. Since molluscs can be predatory hunters they needed to be able to see images so they knew when to act on their prey. While evolving the mollusc's eye opening narrowed and with that the picture projected on the retina became more focused
Molluscs
Arthropods
Looking at Arthropods we can see several similarities between their eyes and ours. In their eyes they have a lens, a transparent cone, light sensitive visual cells, pigment cells, and they have cells that trigger nerve impulses. In arthropods they can see in colour. Since this phylum has very compound eyes they have a part called the ommatidia, this is a cluster of photoreceptor cells surrounded by supporting and pigment cells.
Arthropods
Echinodermata
Echinoderms do not have complex eyes. Animals such as starfish, sea anemones, and sea cucumbers only have simple eye spots at the end of every arm that can sense light and dark.