PORIFERA: The Sponges
These are known as the 'pore bearers', including demosponges- tube sponges- and calcarea- hard sponges. The softer sponges are made of either spongins (flexible protein fibres in their internal skeleton), while the harder ones are made of spicules (made of calcium carbonate or silica) . Sponges are sessile, which means they do not move; controversial to motile organisms. They have no mouth or digestive system, and are filter feeders, which refers to how they churn water through their pores to filter out tiny food particles. The food is held in their choanocytes, commonly known as collar cells. After they trap it, their motile cells called amoebocytes deliver the nutrients to other cells, since they do not have any digestive organs. The amoeboyctes also create eggs for sexual reproduction. Digestion, as explained, takes place in their cells, known as intracellular. Most sponges live in a marine environment; very few can live in fresh water. They are acoelomates, meaning they do not have a body cavity, and have no symmetry- they are asymmetrical. For reproduction, sponges reproduce either sexually using internal fertilization with sperm and egg or asexually by budding and producing gemmules in extreme conditions. They also have no specialized tissues or cells, so they have to undergo circulation by diffusion when in water. For excretion, they also use diffusion. Their collar cells have sperm attached to the end, which circulate water through their excurrent pores and out a large hole at the top- called an osculum- to remove wastes. Sponges have no nerves or nervous system. For respiration, diffusion is used again for oxygen in and carbon dioxide out, dissolved in water of course. A diagram of a typical Porifera is shown below. |
CNIDARIANS: The Stingers
We call these 'stingers' because it includes the Hydrozoa (hydras), Anthozoa (coral and anemones), and Scyphozoa (jellies), which all sting and can harm other organisms. These are also sessile, but are the first organism to move around. They are motile when in their free swimming form in the medusa stage. Both polyps and medusas use an evolved part called a hydrostatic skeleton, allowing the polyp to get taller and the medusa to use jet propulsion to move. Cnidarians also, unlike Porifera, undergo Alternation of Generations, in between a sessile polyp stage and a motile medusa stage. Cnidarians also have a new evolved feature known as a stinging cell, called a cnidocyte, which contains a nematocyst. When an organism brushes against the Cnidarian, the cnidocyte acts as a harpoon gun and the nematocyst acts as a harpoon. The cnidocytes shoot the nematocysts into the prey and pump venom into them, either paralyzing or killing them. Cnidarians typically live in marine environments, with few in fresh water, just like Porifera. However, they have radial symmetry and two germ layers- ectoderm and endoderm- while sponges have no symmetry at all and only a single germ layer. Cnidarians are also acoelomates- they have no body cavity. For reproduction, cnidarians can also reproduce asexually by budding (a polyp), but reproduce sexually by external fertilization, while Porifera reproduce sexually by internal fertilization. Just like sponges, the stingers have no circulation system and use diffusion in water for circulation, excretion, and respiration with no difference from Porifera. Cnidarians in total have three evolved traits from a sponge. First, they have the first known stomach, called a gastrovascular cavity. They also have the first mouth and anus, which exist as a single opening. Last, the digestion takes place extracellular, or outside of their cells. For a nervous system, Cnidarians have no brain, but have a nerve net that a Porifera doesn't have. They also have eye spots, known as ocelli, which detect light in their environment. Their statocysts are special cells that detect gravity in their environment. A typical Cnidarian is shown below. |
PLATYHELMINTHES: The Flatworms
This phylum includes the Phylums Turbellaria (Planaria), Trematoda (Flukes), and Cestoda (Tapeworms). They are free swimming, parasitic (but the Planaria aren't), and have a flat body structure. They have an evolved structure called a pharynx, which serves as both a mouth and an anus. They also are the first organism to use cephalization, which results in them forming a head. Flatworms live in marine and fresh environments, but they also have evolved to live in a host, or another organism's body. For symmetry, Platyhelminthes are bilaterally symmetrical, while Cnidarians are radially symmetrical. They also are triploblastic, which means they have three germ layers- and endoderm and an ectoderm, and a mesoderm layer between those two. Platyhelminthes are the first organism to exhibit this trait. However, flatworms are coelomates, just like sponges and stingers. To reproduce, flatworms reproduce asexually through fission and regeneration, referring to how they split in half and each side grows back to look like the original. The act of regeneration is unlike another organisms shown before such as Porifera and Cnidarians. They also can reproduce sexually through internal fertilization, but they are hermaphroditic, which means they have both male and female sex organs on the same organism. Flatworms decide who is going to hold the eggs using a strange ritual called penis fencing. This refers to how they rear up, extend their penis', and try to fertilize each others eggs. These battles can go on for hours on end, with the female having to go find food and the male to go about his day! For circulation and respiration, flatworms use diffusion, again just like Porifera and Cnidarians. They digest food by taking it in through their pharynx, then digesting it in the many advanced folds of their gastrovascular cavity. They filter their wastes using an evolved item called flame cells. Flatworms have a very unique nervous system called a ganglia, which acts as their nerve net. They also have a nerve ladder with a traverse, and a head with ocelli. These ocelli have photoreceptors that detect light. A diagram of a typical Platyhelminthes is shown below. |
NEMATODA: The Roundworms
This consists of the hookworms, pinworms, and Ascaris worms. Unlike flatworms, roundworms have a cylindrical shape, but are both free swimming and parasitic. They are also the first organism to display their mouth and anus on separate holes on either side of their body. Roundworms can live in marine, fresh, or host environments. For a body plan, they exhibit bilateral symmetry, and have three germ layers; they are triploblastic. Unlike the first three organisms I explained, they are pseudocoelomates, meaning they have a "false coelom." For reproduction, roundworms reproduce only by sexual reproduction, and each worm is either male or female- for the first time! There are very few roundworms that are hermaphroditic. They reproduce through internal fertilization, by the male grabbing onto the female using a hook on its posterior end. Again, for circulation and respiration, they only use diffusion. For digestion, since they have their mouth and anus as different openings, they are the first organisms that have a complete digestive system. To excrete wastes, they also use flame cells, but they are more advanced than flame cells used by Platyhelminthes. Their anus excretes the solid wastes. Nematoda have a primitive brain for a nervous system, as well as a dorsal and ventral nerve cord, which we refer to as a 'true cord'. There are generally six different types of roundworms. The first is Ascaris, which live in your small intestine, causing malnutrition when they absorb digested food. They are usually spread by eating unwashed vegetables. The next are hookworms, which feed on blood from the intestine and enter through your toes. Pinworms can live in your lower bowel, and the females migrate to the anus at night to lay eggs. This is spread orally when the person scratches their anus. Trichinella is spread through eating undercooked pork, and invade muscles and organs, resulting in large cysts. There are also filarial worms, which live in your lymph ducts, blocking them. This results in Elephantiasis since fluids can't drain from the ducts, causing swelling. The last type is the Guinea Stick Worm, found only in Africa. They enter a host when the person is in contaminated water, burrowing through the skin and causing an open wound. The only way to remove it is through wrapping the end around a stick and turning it very slowly- about one turn per day. Below is a typical diagram of a Nematoda. |
ANNELIDA: The Segmented Worms
This phylum includes the Oligochatea- the earthworms-, the Polychaeta- the sandworms-, and the Hirdudinea- the leeches. Annelids are where you first see simple segmentation, with a little bit of specialization. These also have a cylindrical shape, just like Nematoda. Segmented worms inhabit marine, fresh, terrestrial, and host environments, so pretty much almost everywhere! They have bilateral symmetry, are triploblastic, and are the first organisms to be coelomates. This refers to how they have a true body cavity to store organs. For reproduction, annelids reproduce sexually with separate sexes on each worm- they are male or female-, with very few hermaphrodites. They reproduce by their clitellum creating a mucous ring for fertilization to occur, forming a cocoon to protect the eggs. They can exhibit both external and internal fertilization, but there are more external then there are internal. An Annelid's circulation is where you see some BIG changes, as they are the first organisms to have a heart, Segmented worms have five Aortic arches that act as hearts, and two large blood vessels that run from their anterior to their posterior. They also have a closed circulatory system, which describes how their blood moves constantly through their blood vessels. Annelids have a complete digestive system, referring to how their mouth and anus are in separate locations. This system also has some coordination- we will see this advance through the phyla. Their major features are the crop, which stores food, and the gizzard, which breaks it down before it goes to the intestine. To excrete wastes, annelids use a new structure called nephridia, which work like a kidney to remove metabolic wastes like ammonia and any excess water. They also have a primitive bladder to remove this water. Segmented worms also have a more advanced brain from a roundworm, known as the cerebral ganglion. This is connected to its ventral nerve cord and its peripheral ganglion. Its nervous system itself detects stimuli, using statocysts for balance and ocelli for detecting light. For respiration, terrestrial Annelids such as earthworms use diffusion through their skin, since they have to stay moist in order to survive. Aquatic Annelids such as sandworms breathe through their gills. A typical Annelid diagram is shown below. |
MOLLUSCA: The Soft Bodies
These are known as the 'soft bodies' because they are all soft bodied organisms. This consists of the Gastropoda- the snails and slugs-, the Bivalvia- the clams and mussels-, and the Cephalopoda- the squids and octopi. Molluscs are quite special organisms, as they have three news characteristics that distinguish them from others. The first is a muscular foot, which takes the shape of many structures to help the mollusc. For example, a flat form for crawling, a spade shape for digging, or tentacles to catch prey. The second is the mantle, which exists as a thin tissue layer that protects the majority of the organism's body. The last is a part of the animal that contains all its internal organs, known as the visceral mass. They also have a shell that holds calcium carbonate, but this does not exist in ALL molluscs. The trait has been lost in organisms such as slugs. Molluscs inhabit marine, fresh, and terrestrial environments, and do not inhabit hosts like Annelids and Nematods. They have bilateral symmetry, are triploblastic, and have a true cavity- they are coelomates like Annelids. For reproduction, molluscs reproduce sexually by internal or external fertilization. Each one is either male or female, with very few hermaphrodites. Molluscs also have plenty of new structures when it comes to circulation. First, they have a true heart- or hearts. They also can have two different types of circulatory systems. Molluscs who don't move as much have an open system, which refers to how blood goes from the heart into sinus' surrounding organs. The faster organisms have a closed system, as they have to get things done a little quicker. Molluscs generally have three different types of feeding. Some such as snails or slugs have a new structure called radula. This refers to tons of tiny teeth attached to a tongue that help to scrape algae off of rocks, drill through shells, and tear prey. Other organisms like clams, oysters, and scallops are filter feeders. They filter water through their gills, and an evolved structure called a siphon allows food to stay in the mucus on the gills. The last type exists in octopi and sea slugs, which use their jaws to eat prey, while some octopi produce a poison to kill them. To excrete wastes, Molluscs use nephridia to remove ammonia, just like Annelids. However, Molluscs have a more advanced and true brain from an Annelid, and also have more advanced sense organs such as eyes. This is a result of parallel evolution. For respiration, Molluscs are the first to have true gills in aquatic types. The terrestrial Molluscs only use diffusion through their mantle. A typical Mollusc diagram is shown below. |
ARTHROPODS: The Jointed Legs
This phylum consists of the Chilopoda- the centipedes-, the Diplopoda- the millipedes-, the Crustacea- organisms with a cephalothorax-, the Arachnida- the spiders, scorpions, ticks, and mites-, and the Insecta- the insects. These organisms all have specialized segmentation, and a tough exoskeleton made of chitin, which must be shed through a new process called molting as growth occurs. Arthropods also have jointed appendages- a new structure that allows for more movement- and a cephalothorax, which is made of a fused head and thorax. Their habitats consist of everywhere! Arthropods also have bilateral symmetry, are triploblastic, and are coelomates. Another new process besides molting is metamorphosis, which we know as the stage where a caterpillar makes a cocoon and turns into a butterfly. For reproduction, arthropods reproduce sexually by internal fertilization, and each organism has a separate sex. Arthropods are also the first organisms to have a true heart, as shown in organisms like the crayfish. They also have an open circulatory system, which means the blood goes from the heart to a large sinus cavity, where it then diffuses into the organs around them. For digestion, they have a complete and coordinated digestive tract that runs through the body. They also have evolved special mouth parts for chewing, for example, jaws, drills, or pincers. To excrete wastes, terrestrial arthropods use new structures called Malpighian tubes to remove ammonia and other metabolic wastes. Aquatic types use either diffusion or structures called green glands, that exist in organisms like crayfish. Arthropods also have a more advanced nervous system, since they have coordination for each of their appendages. This exists in their ventral nerve cord that connects to the ganglia. Plus, they have a new evolved structure known as a compound eye, which is made up of thousands of tiny lenses that detect colour motion, while their antennae detect chemicals. For respiration, arthropods like crabs and lobsters use gills while organisms like grasshoppers use tracheal tubes that run throughout the body. The air enters into these tubes through the grasshopper's small holes on their side, known as spiracles. Spiders also have structures called book lungs, which are made like pages of a book for respiration. A typical diagram of an arthropod is shown below. |
ECHINODERMATA: The Spiny Skin
This includes the Asteroidea- sea stars-, the Echindoidea- sea urchins-, the Holothuroidea- sea cucumbers-, the Ophiuroidea- brittle and basket stars-, and the Crinoidea- sea lilies and feather stars. Echinoderms all have penta-radial symmetry (meaning they are divided into five parts) , and an internal skeleton instead of an exoskeleton. They also have evolved tube feet that help anchor them to the sea floor and capture prey. Echinoderms also have a water vascular system that aid in respiration, movement, and feeding. They typically live in marine environments only. Echinoderms also are triploblastic and are coelomates. For reproduction, they generally reproduce sexually by external fertilization, since they live in water. Each organism has a separate sex. They can also reproduce asexually by regeneration, but they have to maintain a central part of the body. Echinoderms have a closed circulatory system to breathe, seen in their water vascular system. They also use their digestive gland to spread nutrients out in the digestive cavity. For digestion itself, they have a one way digestive tube, referring to how their mouth and anus are at different locations. They are typically either herbivores, filter feeders, detritivores, or carnivores. To excrete wastes, they use their skin and their tube feet. Echinoderms have a relatively basic nervous system. They have both oral and radial nerve cords, as well as eyespots to detect light and statoycsts to detect gravity. For respiration, they go through diffusion using their water vascular system. They also use their tube feet, skin, and gills. A typical diagram of an echinoderm is shown below. |
UROCHORDATA: One example of this is the tunicates. The adult form of this phylum exists as a sessile filter feeder, which really shows no resemblance to any chordate. They also have neither a dorsal nerve cord or a notochord. Urochordates typically have highly motile larvae, but they unfortunately exist as very small tadpoles. However, these larvae are the first to show all the chordate features. Since the larvae are motile and feeding animals, there is a huge advantage since they can distribute the species. But they only live for about one to two days, and do not have the ability to reproduce. In order to get to the next step of evolution, there would have to be a longer living tadpole that could also reproduce. Shown to the right is a tunicate.
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CEPHALOCHORDATA: One example of this is a lancelet. Cephalochordates are typically known as the "classical chordates" as they are the only organisms that have all of the traits of a chordate as an adult. They also exhibit segmentation, and are believed to have a common ancestor with many other vertebrates. Shown to the right is a lancelet.
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AGATHA: These are the jawless fishes. They were much more dominant in the earlier oceans, as they existed as mud suckers and filter feeders. Jawless fishes, hence the name, have no working jaws. However, they have very evolved gill that help with oxygen uptake, improving levels of activity. They also have no paired appendages. Some examples, are lamprey (top right) and hagfish (bottom right).
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CHONDRICHTHYES: These are the cartilaginous fishes. They were also much more dominant in early oceans. Their skeleton is made of cartilage, not bone, making them secondarily evolved. They also have working jaws that function using 2 pairs of anterior gill slits. However, they have no operculum or air bladder. Their streamlined body and fins allows them to steer, and strong senses like smell make them very well adapted to life. Almost all of them exist as predators! For reproduction, they exhibit internal fertilization, and carry all eggs inside of the female with no nutritional connection. The young organisms are expected to swim once born. Some examples are sharks (top right), skates (middle right), and rays (bottom right).
Although skates and rays look similar, they are quite different: - Skates are round while rays are kit shaped. - Skates have thick heavy tails with no spines while rays have thin barbed tails with spines. - Skates have thorns on their tail and back while rays have no thorns on their tail or back. - Skates have an elongated nose. - Skates are smaller while rays are larger. - Skates lay eggs while rays give birth to live young. |
OSTEICHTHYES: These are the bony fishes. They have a calcified skeleton, and are generally very dominant in water. They have an operculum, and air bladder (unlike Chondrichthyes), which evolved off of the pharynx as a small pocket. They also developed a variety of structures that help them move vertebrates onto land.
For circulation, bony fish have a two chambered heart, which circulates blood from the gills to the remainder of the body. Their nervous system is organized like a basic brain of a vertebrate, with advanced senses. To reproduce, bony fishes external reproduction. After birth, there is very little care from the parent. The young fish are born with the ability to swim and feed, and all have to fend for themselves- without their parents! For excretion, they have a dorsal kidney that removes ammonia from the body. There are two groups of Osteichthyes: - TELEOSTS: These are the true fish with finned appendages. Most of these have adapted from fresh water, then traveled back to oceans. Some examples are salmon (shown on top right) or trout- basically many common types of fish. - LUNG AND LOBE- FINNED FISH: These both evolved from fresh water during times of severe drought. Most lung fish have been spotted in areas like Africa and South America. Lung fish (shown on middle right) and lobe- finned fish (shown on bottom right) also use their crude lungs to help swallow air and help their gills, as most live in stagnant water. However, the lobe- finned fish live mostly on the bottom of oceans, using their fins to hold on to swamp floors and muddy shores. Both types of fish also have a very well known fossil record. |