Learning Objective
By the end of this lecture, you should be able to list out the several phyla of the animal kingdom and their characteristics. You should also be able to list out examples of animals in each phylum. Remember, you are to go nowhere if you are not able to score upto 70% in the quiz.
Introduction
Classification of Animals is the largest topic in ANP 101 and I want you to pay very close attention to this topic because this is where majority of your exam questions will be set from.
You want to get A in ANP 101? Then sit upright, read slowly, and digest the content on this page. Once you're able to, your A is sure.
So let us dive in straight into the lecture.
The varieties of living organisms in this wide world is so large that if we want to start writing on every living organism, we would spend years.
The work however has been reduced for us by scientists who devoted their time into checking out for physical appearances, physiology, behaviour and anatomy of every living organism.
They were successful in their findings, so they classified all living organisms according to the shared or common characteristics between them.
In our context we will be discussing only on Animals. For plants see Bio 101/BOT101
How do scientists classify Animals | How are Animals classified
First, let me put myself in the shoes of these scientists. Assuming all scientific books and journals in this world were burnt and I'm given the task to start classifying living organisms once again, how would I do that?
You see, when classifying organisms, the first thing I would do is taking a few things into consideration. For example, some organisms are visible to the naked eye, some are very small that they can only be detected using a microscope, while others can only be determined by chemical tests. Examining all Living organisms with these features leaves one part of my mission accomplished.
Up next is for me to begin examining the physical structures and sizes of these animals.
When I say physical structures, I mean the physical parts I can see, like the legs in goats and fin in fish while snails have none. You can see, goats, fish and snail can quickly be classified under different sections because of their differences in physical structure. Others that have same structure, I will add them to the table. My work is getting complete bit by bit.
When I'm done with the physical structures and sizes of living organisms, I start looking at how the organisms function, Systematically I am examining the physiology of these organisms. Some organisms give birth to their young ones alive, others have to lay eggs while some others simply divide into two. With these three different functions, I can group several organisms again.
Up next, I start taking into consideration the different organs and tissues that I will see in some set of organisms and I won't see in some. Here, I am Systematically classifying the organisms according to their anatomy. I basically don't know how I'm going to do this because though I'm a scientist, I don't like seeing blood. Infact if you kill a live chicken in my presence I won't join you in eating it. You don't know me who's writing this so I can talk anyhow I like LMAO. Atleast you won't see me on campus and come and stop me. So, I am going to probably give some neat butchers this work to do. Some organisms have three chambered heart, some have four chambered heart, some have two chambered heart while many others do not have hearts. Some also have lungs and others do not have. I can essentially use these features to again slim down my classification table.
I hope you are following me?
Yes? Let's ride on!
By examining these features, it is very easy for me to bring out my neatly classified table of living organisms.
In summary, classification of living organisms into a formal system is based on similarities such as internal and external anatomy, physiological functions, genetic make up or evolutionary history.
The field of study that is concerned with identifying and determining how to place living organisms in the classification table is called TAXONOMY.
Scientists classify all organisms in this order:
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
These are shortened by me as: KPC - OF - GS pronounced as |Kay-pee-cee| |of| |gee-es|
Please I need you to commit that to memory so you can quickly remember even when you're asleep.
When a new living organism is discovered, scientists examine all what I previously explained and then a scientific name is given to the organism.
Scientific name is used for animals while botanical name is used for plants which is out of our context.
Scientific names are taken from the Genus name and Species name of the organism. These names are in Latin and they distinguish an animal from another because no two different animals can have the same genus and species name.
Other features that are used to classify Living organisms
Embryology: This is concerned with the early stages of an organism's development.
Ethology: This is concerned with the behaviour and behavioural pattern of an organism.
Habitat: This is concerned with the places where an organism can be found. The role an organism plays in its habitat helps in classification.
Fossil Records: This is concerned with evolution of organisms and it helps to learn how certain animals have changed and evolved through Earth's history.
Why do we classify Living organisms
Classification of organisms creates a standard way for scientists around the world to communicate about the same organism.
Classification of organisms minimizes confusion, especially when common names are used for those organisms. For example, the normal Lagos black rat, white rat and bush rat, are all several kinds of rat but if I say rat, you wouldn't know if I was talking about the black rat, white rat or bush rat. Classification stops all that.
In your exam you may see the bird 'Robin'.
The bird that Europeans call Robin is different from the ones Americans call Robin. Take a look at this picture below. Do the birds look same?
No!
The bird European call Robin is Erithacus rubecula while the American Robin is Turdus migratorius (A question on that may appear in your exam).
Hierarchy of Classification
Species
Species refers to closely related group of organisms that look exactly the same. There's no difference between species except little features that come with variation.
The local dogs in your area are one specie, and they are different from the Alsatians or German shepherd which belongs to another specie.
I want you to note that only individuals of a single specie can mate and produce viable offspring with one another but almost never with members of other species.
However, in some cases, separate species have been known to produce hybrid offspring (for example, the horse and the donkey producing the mule), but, because the offspring are almost always inviable or sterile, the interbreeding is not considered successful.
For this reason, there was sometime some kind of news spread that a girl mated with a dog and she gave birth to something that looks like dog and human. I simply laughed it off and told my friends that this is the work of Photoshop. Humans and dogs most definitely cannot interbreed because we are not the same specie.
Genus
A group of several species that have some characteristics in common is referred to as genus (genera in plural).
Talking about the white rat, normal Lagos rat, rodents, etc they all belong to a genus.
Family
A group of several genera that share only some characteristics is referred to as Family.
Individuals of the same Family only share some specific features in common I won't want to go too far so I'll continue staying within our context.
Order
A group of several families that share a few characteristics in common is referred to as order
Class
A group of several orders that share some features is referred to as Class.
Phylum
phylum is used in the animal kingdom while division is used in the plants kingdom. Phylum is a group of several classes that have only few features in common.
Kingdom
Kingdom is the broadest range of classification and it groups several phyla into one.
Some scientists go ahead to group kingdoms into Domain but that is none of our concern here.
We have five kingdoms which includes all living organisms except virus:
- Monera (Prokaryotae)
- Protista
- Fungi
- Plantae
- Animalia
Classification methods
Traditional classification or Classical approach
Traditional method of classification is the type of classification which taxonomists use and we generally accept. They classify several Animals into different Phyla, phyla into classes, classes into order... like mammals, fish, birds etc
Phenetics approach
In the phenetics approach, scientists identify a set of characteristics. They now measure that characteristics (or feature) in different animals.
Afterwards they assign a certain numerical value to each characteristic.
The tally is used to determine the extent of similarity between different organisms.
For example, pheneticists may find that, overall, birds and reptiles have a 77% similarity of body structure, or morphology, compared to a 55% morphological similarity between birds and mammals. From this measurement, pheneticists would suggest a classification that grouped birds and reptiles more closely than birds and mammals.
In summary, phenetics approach involves measuring different characteristics and using them to propose similarities between different organisms.
Cladistic approach
In cladistic approach, evolutionary trend is used here. Cladists use the fossil record, molecular genetics, and other techniques to create an evolutionary tree called a cladogram.
This diagram shows the relationship of a group of species based on the fewest number of shared changes that have occurred from generation to generation.
History of classification
Classification is one of the oldest sciences, but despite its age it is still a vigorous field full of new discoveries and methods.
One of the earliest classification schemes was established by Greek philosopher Aristotle, who lived in the 300s bc.
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Aristotle believed that the complexity of life could be divided into a natural order based on dichotomies, or polar opposites. For example, Aristotle divided animals into those with blood and those without blood, a classification that roughly corresponds to the division between vertebrates and invertebrates used in contemporary classification schemes.
Aristotle wrote extensively on both plants and animals, but his writings on plants were lost.
Fortunately, his pupil Theophrastus applied Aristotle’s taxonomic approach to the study of plants in his work Inquiry into Plants (trans. 1916).
Theophrastus subdivided plants, based on shape, into broad categories such as trees, shrubs, and herbs.
A more pragmatic approach to classification was developed by Greek physician Dioscorides, who separated, for instance, medicinal herbs from those used in making perfumes.
He translated the common names of organisms into Latin (the language of educated persons at that time). These names were often long and difficult to remember, and included numerous descriptive terms.
This complex naming process was simplified into a two words, or binomial, naming system in the mid-16th century to mid-17th century by a group of naturalists known as herbalists.
Sixteenth-century Italian botanist Andrea Cesalpino was the first scientist to classify plants primarily according to structural characteristics, such as their fruits and seeds.
Cesalpino developed a method of character weighting in which he defined certain key characteristics that were important for recognizing plant groups. This method was adapted by Swiss botanist Caspar Bauhin, who catalogued an extensive list of plants.
More importantly, Bauhin was the first to organize plants into a crude system that resembles modern genera and species. Animal classification also advanced in the 16th century.
French naturalist Pierre Belon extensively studied and catalogued birds. He was the first to use adaptation to habitat to divide birds into such groups as aquatic birds, wading birds, birds of prey, perching birds, and land birds, categories still used informally today.
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In the 17th century, English naturalist John Ray was the first to apply the character weighting method to structural features in animals. He used key characteristics, such as the shape and size of the bird beak, to classify birds.
In the mid-1700s, Swedish naturalist Carolus Linnaeus developed formal rules that provided consistency for a two-name system in common use called the binomial system of nomenclature.
In this system, similar organisms are grouped into a genus, and each organism is given a two-word Latin name.
The first word is the genus name, and the second word is usually an adjective describing the organism, its geographic location, or the person who discovered it.
Using this system, the domestic dog is Canis familiaris. Canis is the genus name for the group of animals that includes dogs, wolves, coyotes, and jackals.
The word familiaris acts as a descriptor to further differentiate the domestic dog from its wild cousins.
Before Linnaeus, biologists had established random categories of classification, such as the category of genus for a group of species.
Linnaeus was the first to formalize the use of higher taxa in his book Systema Naturae (1735), establishing the standard hierarchy taxonomy still in use today.
Before the 19th century, Linnaeus and other taxonomists classified organisms in an arbitrary but logical way that made it easier to communicate scientific information.
However, with the publication On the Origin of Species in 1859 by British naturalist Charles Darwin, the purpose of classification took on new meaning.
Darwin argued that classification systems should reflect the history of life—that is, species should be related based on their shared ancestry.
He defined species as groups that have diverged from a shared ancestry in recent history, while organisms in higher taxa, such as genera, class, or order, diverged from a shared ancestor further back in history. Making evolutionary history compatible with the classification systems already established was no easy task.
Critics argued that classification should be consistent with phylogeny (history of the evolution of a species or group), Yes! but not based solely upon it.
They advocated using other factors, such as behavior or anatomy, along with phylogeny to better classify organisms.
This controversy over the fundamental approach to classification continues today.
The development and use of microscopes in the late 16th century revealed a diverse array of single-celled organisms. These organisms presented new classification problems for the science community, which still relied on a two-kingdom classification system.
At first, single-celled organisms that carried out photosynthesis were classified in Kingdom Plantae, and organisms that ingested food were placed in Kingdom Animalia.
By the 19th century, scientists had identified a wide variety of microscopic organisms with diverse cell anatomies, specialized internal structures called organelles, and reproductive patterns that did not easily fit into the plant or animal classification system.
This great diversity prompted German biologist Ernst Haeckel to propose placing these unicellular forms in a third kingdom, the Protista.
Haeckel placed bacteria within the Kingdom Protista in a separate group that he called Monera, recognizing that these organisms differed from all other cells because they lacked nuclei.
As biologists learned more about bacteria, they became aware of the further differences between these organisms and all other life forms. In addition to lacking nuclei, bacteria differ from other types of cells in that they do not have membrane-bound organelles.
In the 1930s, these differences led French marine biologist Edouard Chatton to make a crucial distinction between prokaryotes, organisms such as bacteria that lack nuclei, and eukaryotes, more complex organisms that have nuclei.
In 1938 American biologist Herbert Copeland argued that the distinctions between prokaryotes and eukaryotes were so fundamental that prokaryotes merited a fourth kingdom of their own called Kingdom Monera (or Kingdom Prokaryotae).
Like all living things, animals show similarities and differences that enable them to be classified into groups. Birds, for example, are the only animals that have feathers, while mammals are the only ones that have fur. The scientific classification of animals began in the late 18th century.
At this time, animals were classified almost entirely by external features, mainly because these are easy to observe. But external features can sometimes be misleading.
For example, in the past, comparison of physical features led to whales being classified as fish and some snakes being classified as worms.
Presently, animals are classified according to a broader range of characteristics, including their internal anatomy, patterns of development, and genetic makeup.
These features provide a much more reliable guide to an animal’s place in the living world.
They also help to show how different species are linked through evolution.
Scientists divide the animal kingdom into several groups, each called a phylum (plural phyla).
Phyla of the Animal Kingdom
We have the following phylum in the animal kingdom:
- Porifera
- Coelenterata (or cnidarians)
- Platyhelminthes
- Nematoda
- Annelida
- Mollusca
- Arthropoda
- Echinodermata
- Chordata
In our context, We will also discuss the protozoa phylum from the protist kingdom because they display some animal-like characteristics (proto: first kind, zoa: animals).
These Animal phyla look long to remember?
Well, I abbreviated the entire phyla using their first letters.
I use PCPNAMAEC. Pronounced as |Pee| |See| |Pee| |Na| |Ma| |heck|.
I want you to spend some time on this to commit it to memory. Find a book and write it down somewhere or write it and paste it on the wall of your hostel (proven way to memorise something)
Classification of Animals. Photo_Credit: NCERT
Now, let us start discussing each of these phylum. Please ensure you read closely and take note of every important point.
Protozoa
Protozoans are unicellular organisms.
They are very small (microscopic) and may range from 2 to 70 microns (2 to 70 micrometers).
They display Animal-like characteristics.
They are placed in the kingdom Protista.
They are eukaryotic in nature (have well defined Nucleus).
They have little to no differentiation (upgrade) into tissue systems. They love their unicellularity like that.
Some of them are parasitic in nature while others are free-living.
More than 20,000 species are known, including familiar ones like paramecium and amoeba.
Most species are found in aquatic habitat like rivers, ponds, oceans and lakes.
Protozoans are Heterotrophic. They obtain their food by ingesting other microscopic organisms in water like bacteria, waste product of other organisms, algae or other protozoa.
Most of the protozoa reproduce asexually mainly by method of Binary Fission.
Protozoa move by using different structures which are Cilia, flagella, false foot or foot-like extensions (called pseudopodia).
Ciliia (Singular: cilium): These are small, hair-like projections which aid locomotion (movement) of protozoa. In addition to locomotive use, cilia are also used to create disturbance in water (water current) to help sweep food particles that will be ingested by the protozoa.
Flagella (singular: flagellum): These are long, flexible whip-like structures that acts as an organ of locomotion.
Pseudopodia (singular: pseudopodium): These are known as false-foot. They are foot-like extensions an Amoeba uses to propel itself.
Most Agriculturally important species of protozoans include: Babesia, Trypanosome, Plasmodium, and Coccidia.
Babesia causes Red-water fever.
Trypanosome causes Trypanosomiasis or sleeping sickness.
Plasmodium causes Malaria fever.
Porifera
Organisms in this phylum are multicellular, they have more than one cell.
They are organisms with holes.
They lack mouth, sensory organs, organized tissues, neurons and muscle cells.
Their body is supported by a skeleton made up of mineral spicules (either calcerous [containing calcium] or siliceous [made up of silicon]) and/or spongin fibres (protein fibres).
They do not move around, they attach to a solid support.
Sponges
They are commonly called sponges (spon-g-iz).
They are generally found in aquatic habitat.
They come in various sizes, colours and shapes like:
Arborescent - Tree-like
Flabellate - Fan shaped
Caliculate - Cup shaped
Tubular - Tube shaped
Globular - Ball shaped
Amorphous - shapeless
Organisms in this phylum are generally asymmetrical (they cannot be divided into separate parts that will be equal to each other).
Their outer layer of cells (what you can reason like their skin) is called pinacoderm and as the sponge matures, the pinacoderm is eventually replaced by the choanoderm.
*Pro tip: Anywhere you see DERM, just know we are referring to body*
This pinacoderm separates the inner region of the sponge (mesohyl) from the external environment.
Choanocytes from the Choanoderm make up the principle of 'pump' and 'filter'.
When water is driven into the sponge (through the small holes [ostia]), it moves in one direction. That is, flow of water inside a sponge is uni-directional.
With the water flowing through the internal cavity (spongocoel), bacteria and other food particles are trapped.
The water then exits the sponge via one or more larger openings (called osculum).
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The food is digested and distributed among the cells of the mesohyl.
The mesohyl cells are the ones that carry out the function of digestion, respiration and reproduction in a sponge.
A sponge can reshape itself (using amoeboid movement) to upgrade or fine-tune its filter-feeding system.
Some of their cells are remarkably like free-living protozoans called collar flagellates. To evolutionary biologists, this resemblance strongly suggests that sponges and other invertebrates arose from protozoan-like ancestors.
Sponges are monophyletic group (that is they have only one common ancestor).
Sponges are hermaphroditic in nature (that is one has both male and female sex organs).
Sponges reproduce asexually by fragmentation and sexually by formation of gametes.
Fertilisation is internal and development is indirect (having a larval stage which is morphologically distinct from the adult).
Examples of porifera or sponges are sycon (Scypha), Spongilla (Fresh water sponge) and Euspongia (Bath sponge).
Coelenterata or Cnidarians
The name cnidaria is derived from the cnidoblasts or cnidocytes (which contain the stinging capsules or nematocytes) present on the tentacles and the body.
Cnidocytes are used for anchorage, defense and for the capture of prey.
Cnidarians are aquatic organisms.
Cnidarians have a sac-like body with a single mouth opening (which also serves as anus) and several tentacles surrounding the mouth.
HydraCnidarians lack internal organs, i.e they do not have digestive, circulatory or respiratory systems.
Cnidarians body is composed of two sheet of cells:
The inner layer (Endoderm) and outer layer (Ectoderm). This makes them Diploblastic (having only two body layers).
A gelatinous (jelly-like) structure called mesoglea layer holds these two cell layers together.
Cnidarians are radially symmetrical (the separate parts are equal when they are divided from the central mouth opening).
Sea Anemone Cnidarians exhibit tissue level of organization [have more body design differentiation than sponges].
Some of the species live in colonies (corals) while some others live in solitary (living alone) e.g hydra.
Some of the cnidarians have skeleton composed of Calcium carbonate, example corals.
Cnidarians exhibit two basic body forms known as polyp and medusa.
The polyp is a sessile (fixed in one place) and cylindrical form of cnidarians like Hydra, Adamsia (Sea anemone), etc.
Polyp-Sessile(Fixed in one place)The medusa is umbrella-shaped and free-swimming cnidarians like Aurelia or jelly fish.
Cnidarians can reproduce either sexually or asexually.
Polyps reproduce asexually by budding (a new organism grows out of a certain region from its parent body). It grows and separates to form a new polyp or Medusae
Medusa on the other hand basically reproduce sexually. They produce gametes (sex cells).
A gamete from a male medusa (sperm) fuses with a gamete from a female medusa (egg) to form a zygote. The zygote develops into a larva, which in turn develops into a polyp or medusa.
Jelly fish MedusaSome Cnidarians exhibit both asexual reproduction (as in polyps) and sexual reproduction (as in medusa). They exhibit alternation of generation (Metagenesis), i.e., polyps produce medusae asexually and medusae form the polyps sexually.
For example, the reproductive life cycle of a jellyfish illustrates both asexual and sexual reproduction: Males release sperm and females release eggs into the water. When an egg and sperm fuse during sexual reproduction, a larva develops which attaches to a rock or other object and develops into a polyp. Using budding, the polyp divides to form a colony of polyps that resembles a stack of saucers. Each saucer in the stack develops tentacles and swims away from the colony as a new medusa, and the reproductive cycle repeats.
Medusa-Free swimmingJellyfish and sea anemones are common examples.
Scientists divide cnidarians into four classes:
- Hydrozoa
- Scyphozoa
- Cubozoa
- Anthozoa
Examples of cnidarians are Aurelia (jelly fish), Physalia (Portuguese man-of-war), Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan) and Meandrina (Brain coral).
Portuguese Man Of WarPlatyhelminthes
The phylum literally means “flat worms” and all the members of this phylum are flat worms!
Flat wormThe phylum is classified into three main groups or classes:
- Turbellaria (Free living)
- Trematoda (Parasitic Flukes)
- Cestoda (Parasitic Tapeworms)
Flat worms are bilaterally symmetrical, i.e, a line that passes through the center can divide them into two equal halves.
Flat worms are triploblastic, i.e, their body layer is divided into three parts: inner layer (Endoderm), middle layer (mesoderm) and outer layer (Ectoderm).
Tape Worm They have no internal body cavity, therefore they are referred to as acoelomates.
They have an incomplete digestive tract.
They basically use flame cells for Excretion.
They are hermaphroditic and they reproduce sexually.
Fertilisation is internal and development is indirect.
The most important agricultural species of platyhelminths is the Liver Fluke (or Fasciola hepatica).
Fasciola hepatica (Liver Fluke)Liver Fluke is a parasitic flat worm and it cause Schistosomiasis in farm Animals.
Understanding the life cycle of the liver fluke is very important in finding ways of controlling the disease.
The Life cycle is complicated and the fluke must lay huge amounts of eggs to survive. The lifecycle takes place in the cow, on grass and in a secondary host (the mud snail).
Life cycle of a Liver Fluke
The Liver fluke lives in the ducts of the liver.
The fluke lays eggs in the bile ducts (20,000 or so a day).
The eggs are released with faeces from the farm animal and hatch two weeks later in water and form a ciliated Miracidium.
When mud snails come around, the Miracidium enters the foot of the mud snail and changes into a Sporocyst.
Still inside the snail, the Sporocyst changes into a Redia.
The Redia then produce very small tadpole shaped Cercaria.
For every Miracidium that enters the snail, 10,000 Cercaria can be produced.
The Cercaria then leaves the snail and goes onto grass.
There it forms a shell (cyst) and waits to be eaten by a sheep or cow.
If eaten, the stomach acids dissolve the cyst and the liver fluke moves to the liver and restarts the cycle.
Understanding the life cycle of the liver fluke allows us control the spread in the following ways:
- Dosing animals to kill the adult fluke
- Spraying molluscicides to kill the snail.
- Drainage (because the snail only lives in water).
- Fencing flooded areas.
- Don’t graze wet lands after August.
Other organisms in platyhelminthes are planaria, tapeworm, etc
Scolex | Hook of tapewormNematoda
Nematodes are also known as roundworms or eelworms. Many of them are parasitic in nature.
Round wormThese worms reproduce by laying thousands of eggs, which become encysted in the grass and wait to be ingested.
The most important species are:
- Lungworms (causes hoose)
- Hairworms (worms in school children)
- Potato eelworm
- Stomach worms.
Nematodes are triploblastic (they have 3 body layers).
Nematodes have a not-too-developed internal body cavity, hence they are referred to as pseudocoelomates.
NematodeThey are the first group of animals to have a complete digestive tract.
They possess thick cuticle (skeletal make up) which prevents digestive enzymes of the host organism from damaging the round worm.
They can be free living, aquatic, terrestrial or parasitic in plants and animals.
An excretory tube removes body wastes from the body cavity through the excretory pore.
They are not hermaphrodites, i.e, males are different and females are different (they are dioecious).
Usually, the females are longer than the males.
Fertilisation is internal and development may be direct (the young ones resemble the adult) or indirect (the young ones look different from the adult).
Common diseases caused by nematodes
- Trichinella- contracted from eating poorly cooked pork.
- Heart worms in dogs.
- Elephantiasis.
Parasitic Roundworm Annelida
Annelids are segmented worms and they include organisms like earthworm and leeches.
The segments allows for specialized movement.
Each segment has four bristles or setae.
Some are aquatic while others are terrestrial.
EarthwormsInternal structures such as nerves, nephridia, blood vessels, and reproductive organs are repeated in several segments.
This makes it that damage to one segment is less harmful to the functioning of a segmented organism.
They have true body cavity and are referred to as coelomates.
They have complete digestive tract and closed circulatory system.
They excrete using nephridia (singular: nephridium).
They are bilaterally symmetrical and triploblastic (3 body layers).
Neural system consists of paired ganglia (singular: ganglion) connected by lateral nerves to a double ventral nerve cord.
LeechNereis, an aquatic form, is dioecious [Sexes are separate], but earthworms and leeches are monoecious or hermaphroditic [having both the male and female reproductive organs in the same individual].
Reproduction is sexual.
Examples are earthworms, hirudinaria, nereis, leeches etc
Mollusca
The molluscs include slugs, snails, squid, mussels, clams and octopus.
They all have one anatomical feature in common, the presence of a shell at some stage in the life cycle. Although most mollusks have a shell as adults, the octopus, squid, and deep-sea forms do not. They do however have a small, shell-like structure, called a shell gland, present for a short time during embryonic development.
One piece shell: Snail
Snail Two piece shells: clams
ClamsEight piece shells: chitons
Mantle is the structure that forms or secretes a shell.
The mantle houses the gills, lungs and reproductive system.
These animals generally have a foot, which excretes a slimy mucus. They also have a rasping tongue.
They are terrestrial or aquatic.
The most agriculturally important mollusc is the mud snail (Lymnaea truncatula).
Mollusks feed by means of the radula (a flexible organ that bears many sharp teeth) which is used to scrape food.
Mollusks use gills to absorb nutrients from water and release waste products from cells.
SquidMollusks have both open and closed circulatory system.
Mollusks are bilaterally symmetrical (two equal halves when divided in one plane).
Mollusks are triploblastic.
Mollusks possess true body cavity (coelomates).
SlugThe head region has sensory tentacles.
Mollusks are usually dioecious.
Classes of mollusks
- Gastropoda- coiled shell; including snails and slugs
- Pelecypoda (Bivalves / Bivalvia)- hinged shells: clams and oysters
- Cephalopoda- head with tentacles: squid, octopus
Examples of mollusks are snail, clams, slug, octopus, squid etc
Octopus Arthropoda
This is the largest phylum in the animal kingdom containing upto millions of species.
All arthropods have jointed legs (or Appendages) and an exoskeleton (outer skeleton).
The body of arthropods is covered by chitin.
The body of arthropods consists of head, thorax and abdomen. Some others have only head and abdomen.
Arthropods are bilaterally symmetrical.
Arthropods are triploblastic (body is made up of 3 layers).
Arthropods bodies are segmented.
Arthropods have true internal cavity (therefore they are coelomate)
Arthropods internal cavity is filled with blood.
There is an open circulatory system, so the blood does not flow in well defined blood vessels.
Respiratory organs are gills, lung books or tracheal system.
Arthropods have sensory organs like eyes (some have simple eyes while some have compound eyes), antennae (long projections on the head).
Excretory organ of arthropods is Malpighian tubules.
Arthropods are mostly dioecious (males are separate, females are separate).
Some Arthropods lay fertilised eggs (fertilisation is internal) while in some others fertilisation is external.
Arthropods are split in 4 classes:
- Crustacea
- Insecta
- Arachnida
- Myriapoda
Crustacea
Crustaceans have two pair of antenna
ShrimpCrustaceans respire using gills.
Crustaceans are majorly aquatic.
Examples are: crayfish, lobster, shrimp and barnacles.
LobsterInsecta
These are the most abundant organisms in the arthropods phylum.
Insects have a head, thorax and abdomen.
AntInsects have one pair of antennae.
Insects usually have 2 pair of wings while some others have none.
Insects have 3 pairs of jointed legs.
Insects have claim to be the most successful animals in the world (to the extent some people fear they might dominate human soon).
They are mainly terrestrial. Some others live in fresh water habitat while few are found in salt water habitats.
They have open circulatory system.
Their respiratory organ is trachea.
Examples of insects: Cockroach, butterfly, praying mantis etc
BeesArachnida
Arachnids have no antennae.
SpiderSome arachnids are parasitic in nature.
Some arachnids have poison glands.
Horseshoe crabSome organisms are afraid of these arachnids and those organisms are referred to as arachnophobics.
Examples of arachnids: spiders, scorpion, ticks, horseshoe crab, mites etc
ScorpionMyriapoda
Myriapods have a pair of antenna.
Myriapods are flexible animals with a lot of legs on both sides of their body.
MillipedeThey are usually segmented.
They move very fast.
Examples of myriapods: centipedes, millipedes.
Centipede Some other interesting features of Arthropods
Some arthropods shed off their skins (moulting) and new ones are formed underneath.
Some arthropods exhibit metamorphosis. This is the changes that is associated with growth and development of an organism. From egg stage, they grow into a small larvae. After sometime, this larvae develops into pupa which finally molts to form the mature adult. This is referred to as complete metamorphosis. Some others exhibit incomplete metamorphosis where it skips larva and pupa stage. From egg stage the organism develops into a nymph which finally develops to a mature adult.
Lobsters claws are modified legs and they really taste good when cooked properly, especially in New Orleans.
LobsterPraying mantis, the females which are usually larger than the males, bites off the head of the male and copulates with the headless male. Then the female eats the male's body. Thus reproducing and finding its food at the same time.
Ticks are blood sucking spiders that attach to sheep and spread disease (red water fever).
Echinodermata
Echinoderms are spiny skinned animals which gives rise to their name (echinodermata).
Echinoderms differ from other animals in that they have a water vascular system that uses seawater to accomplish respiration, locomotion, and reproduction (blue blooded).
Star fishEchinoderms are mainly aquatic organisms.
Echinoderms are bilaterally symmetrical in the larvae stage and radially symmetrical in the adult stage.
Echinoderms have rings of nervous tissues but no centralized brain.
Echinoderms are triploblastic.
Echinoderms possess true internal cavity.
Sea urchinDigestive system is complete.
An excretory system is absent.
Echinoderms regenerate.
Sexes are separate (dioecious). Reproduction is sexual. Fertilisation is usually external.
Echinoderms have tube feet.
Among the major Animal phyla, the echinoderms are the most distinctive and unusually shaped.
Sea cucumber They include starfish, sea urchins, and sea cucumbers and are the only animals with a five-pointed design.
They live in the sea and move with the help of tiny fluid-filled feet—another feature found nowhere else in the animal world.
Star fishChordata
Animals in the Chordata phylum are categorized basically due to their possession of a notochord, a dorsal hollow nerve cord and paired Gill slits.
Chordates possess a post anal tail and a closed circulatory system.
Chordates are bilaterally symmetrical.
Chordates are triploblastic (body is made up of three layers).
Chordates have true internal cavity (therefore they are coelomates).
Chordata phylum is sub-divided into three subphyla:
- Urochordata or Tunicata
- Cephalochordata
- Vertebrata.
Urochordata and Cephalochordata are referred to as protochordates and they are basically aquatic.
In Urochordata, backbone is present only in larval tail.
In Cephalochordata, backbone extends from head region to tail region and is persistent throughout their life.
Examples of urochordata: Ascidia, Salpa, Doliolum.
Examples of Cephalochordata: mphioxus or Lancelet.
Vertebrata
These are the true vertebrates in the animal kingdom.
These animals have a true vertebral column and an internal skeleton.
The members of Vertebrata possess notochord during the embryonic period.
The notochord is replaced by a cartilaginous or bony vertebral column in the adult.
This leads us to say, all vertebrates are chordates but all chordates are not vertebrates.
Besides the possession of backbone, vertebrates have a ventral muscular heart with two, three or four chambers.
Kidneys are used for excretion and osmoregulation.
Paired appendages which may be fins or limbs.
Vertebrata is divided into five major classes:
- Pisces
- Amphibia
- Reptilia
- Aves
- Mammalia
PISCES
Pisces is the class that contains all fishes with backbone (excluding whale).
Fishes are cold blooded. This means that they do not regulate their body temperature, their body temperature changes with respect to its environment. Hence they are referred to as Poikilothermic or Poikilotherms.
Fishes are majorly aquatic (unless you have seen a fish walk on land before).
Some fishes however can survive for several minutes on land (example catfish) but they cannot dwell fully on land.
Fishes have two chambered hearts.
Fishes have their appendages as fins.
Fishes are dioecious.
Fertilisation is external.
Fishes possess homodentition (their teeth is of only one type).
Fishes bodies are totally covered in scales.
Examples of pisces: Tilapia, other regular fishes that you know or I should start listing them out for you? Don't tell me Titus, shawa and kote else I will just bomb you. Call them names like the real scientist you are.
AMPHIBIA
Amphibia is a class that contain organisms that are both aquatic and terrestrial.
These organisms are the first to be able to dwell on land successfully.
Amphibia (Left)Amphibians are also cold blooded organisms: they are Poikilothermic.
Amphibians have three chambered heart.
Amphibians have a smooth and slimy skin.
Amphibians breath through their skin as well as their lungs.
Amphibians have their appendages as limbs.
Amphibians possess homodentition (only one type of teeth).
Amphibians are dioecious and they fertilize their eggs externally, some fertilizes internally though.
Examples of amphibians: frog, chameleon etc
REPTILIA
Reptiles contain organisms that are majorly terrestrial while others are aquatic.
They are cold blooded or Poikilothermic.
Their bodies are covered completely in scales.
Some reptiles have their appendages as limbs (like tortoise or crocodiles) while it is regressed in others (like snakes).
Reptiles are dioecious and fertilisation is internal.
Some reptiles lay fertilised eggs while some others give birth to their young ones alive.
Reptiles have three chambered heart.
Reptiles breathe using lungs.
Examples of reptiles: snake, crocodile, etc
AVES
Aves or birds are one of the Agricultural important class of animals.
Birds are warm blooded (homeothermic) animals. This means they regulate their body temperature.
Birds are covered in feathers.
Some fly while others do not.
Birds have hollow, light bones.
HummingbirdBirds do not have teeth (no dentition).
Birds have four chambered heart.
Birds have their appendages as wings and limbs.
Birds have no bladder.
Guinea fowlBirds are dioecious.
Fertilisation is internal.
Birds lay fertilised eggs.
Examples of aves: fowl, turkey, black kite etc
TurkeyMAMMALIA
Mammals are the most complex of all animals.
Mammals basically give birth to their young ones alive.
RabbitMammals have four chambered heart (two ventricles, two auricles).
Mammals are homeothermic (they regulate their body temperature).
Mammals are covered in fur or hair.
Mammals have their appendages as limbs.
WhaleMammals exhibit heterodentition (their teeth are of various sets and types).
Mammals are dioecious.
Fertilisation is internal.
Examples of mammals: whale, kangaroos, etc
Sea LionAnimal life spans vary from less than 3 weeks in some insects to over a century in giant tortoises. Some animals, such as sponges, mollusks, fish, and snakes, show indeterminate growth, which means that they continue to grow throughout life. Most, however, reach a pre-defined size at maturity, at which point their physical growth stops.
Summary
☑️ Classification, identification, naming, and grouping of organisms into a formal system are based on similarities such as internal and external anatomy, physiological functions, genetic makeup, or evolutionary history.
☑️ Taxonomy is the field of study that deals with identifying and classifying organisms.
Scientists give a scientific name to animals which comprise of two Latin words to distinguish it from other animals.
☑️ When classifying organisms, scientists study a wide range of features, including those visible to the naked eye, those detectable only under a microscope, and those that can be determined only by chemical tests.
☑️ The base level in the taxonomic hierarchy is the species.
☑️ Species is a group of closely related organisms that are able to interbreed and produce fertile offspring.
☑️ Hierarchy of Classification:
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
☑️ Traditional approach to classification make use of physiological and anatomical similarities between organisms.
☑️ Phenetics approach to classification make use of measurement of characteristics and features to weigh similarities between organisms.
☑️ Cladistic approach to classification make use of evolutionary history or phylogeny to classify organisms.
☑️ Animal Kingdom is divided into several phyla which are:
- Porifera / sponges.
- Cnidarians.
- Platyhelminthes.
- Nematoda.
- Annelida.
- Mollusca.
- Arthropoda.
- Echinodermata.
- Chordata.
☑️ Protozoans are protists that display Animal-like characteristics.
☑️ One of the most agriculturally important species of Protozoans is Babesia. This protozoa causes Red-water fever.
☑️ Amoeba is one of the most common protozoans moves by means of pseudopodia.
☑️ Porifera are very simple, filter feeding animals with so many holes.
☑️ They exist in various shapes:
- Cup shaped: caliculate
- Fan-shaped: flabellate
- Tubular: tube-shaped
- Globular: round shaped
- Amorphous: shapeless
☑️ The pinacoderm lines the internal canals and is eventually replaced by the choanoderm.
☑️ The flow of water inside a sponge is unidirectional.
☑️ Cnidarians are invertebrates (animals that lack a backbone), but the ectoderm of some cnidarians, including hard corals and some hydrozoans, may form a skeleton-like structure externally.
☑️ The ectoderm and endoderm layers of cnidarians contain contractile fibers that enable the animal to move about.
☑️ Cnidarians are given their names because of their possession of cnidocytes.
☑️ Mesoglea holds the ectoderm and Endoderm layers of cnidarians.
☑️ Platyhelminthes are flat worms.
☑️ They comprise of 3 major classes:
- Turbellaria
- Trematoda
- Cestoda
☑️ They are hermaphrodites.
☑️ They include parasitic flukes (Fasciola hepatica) and tape worm.
☑️ The life cycle of liverfluke takes place in a cattle, on grass and in secondary host (mud snail).
☑️ For every miracidium that enters the snail, 10,000 cercaria can be produced.
☑️ The most important species of nematodes are:
- Lungworms
- Hairworms
- Potato eelworm
- Stomach worm
☑️ Annelids are segmented worms.
☑️ Annelids have four bristles on each segments called setae.
☑️ Mollusks generally have shells at one point of their lifetime.
☑️ Mollusks generally have a foot, which excretes a slimy mucus. They also have a rasping tongue.
☑️ One piece shell mollusk: snail
Two piece shells mollusk: clams
Eight piece shells mollusk: chitons
☑️ Classes of mollusks are:
- Gastropoda
- Pelecypoda
- Cephalopoda
☑️ Arthropoda is divided into four classes:
- Crustacea
- Insecta
- Arachnida
- Myriapoda
☑️ Echinoderms are spiny skilled, flexible aquatic animals.
☑️ Echinoderms have tube feet and no Centralized brain.
☑️ Chordata is the most complex phylum of animals.
☑️ Chordata comprises of the only vertebrates in the entire animal kingdom.
☑️ Vertebrata, a subphylum of chordata comprises of the true vertebrates.
☑️ Vertebrata is divided into four classes:
- Pisces (Fishes)
- Amphibia (toads)
- Reptilia (crawlers)
- Aves (birds)
- Mammalia (mammals)
To get full details on any Animal, especially for those in COLANIM, I'll recommend https://animaldiversity.org you will get full details and full classification names of every animal you ever want to know of.
Test Questions
TEST: CLASSIFICATION OF ANIMALS
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TEST: CLASSIFICATION OF ANIMALS
Total Questions: 30
you'll have 30 second to answer each question.
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Quiz Answers
1. Classification, identification and grouping of organisms into formal system are based on...
Internal and external anatomy, physiological functions, genetic make up or evolutionary history
2. Organisms in phylum protozoa that are of agricultural importance includes
Trypanosome, coccidia, paramecium and amoeba
3. Trypanosome is a dangerous protozoa parasite which affects mostly the cattle and is transmitted by
Tsetse flies only
4. Scientists divide Cnidarians into 4 classes which are
Hydrozoa, scyphozoa, cubozoa, anthozoa
5. The pinacoderm of the phylum porifera lines their internal canal and is eventually replaced by...
Choanoderm
6. Nematodes are also known as...
Round worms or eel worms
7. Echinoderms are characterized by
Vascular water system that is used for locomotion, ring of nervous tissue with no centralized brain
8. The correct order of classification is
Species, genera, families, order, classes, phyla, kingdom
9. Cnidarians are characterized by _ specialized stingy cells which gives the phylum its name
Cnidocytes
10. When classifying organisms, scientists study a wide range of features which includes those
Visible to the eye, those detectable under microscope, or those determined by chemical tests
11. Which of the following is not considered while classifying organisms
External shapes and sizes of spermatozoa, anatomy, physiological function, embryology, habitat, fossil record
12. Scientists classify organisms using hierarchical categories called...
Taxon
13. The base level in the taxonomy hierarchy is the...
Species
14. _ is a group of closely related organisms that can interbreed to produce fertile offspring
Species
15. _ is the collective name for animal like unicellular organisms, some of which may form a colony
Protozoa
16. Most species of protozoa are motile either by...
A, B and C are correct
17. The non-motile or sessile body form of a cnidarians is known as...
Polyp
18. The free swimming body form of a Cnidarian is known as...
Medusa
19. The scientific name for the American Robin is...
Turdus migratorius
20. Fan shaped sponges are called...
Flabellate
21. Cup shaped sponges are called...
Caliculate
22. One of these is not a phylum of the animal kingdom
Protozoa
23. Cnidarians have a sac-like body with two openings
False
24. _ is a gelatinous layer that holds the Endoderm and ectoderm of cnidarians
Mesoglea
25. In the life cycle of a Liver Fluke, a miracidium can produce upto _ cercaria
10,000
26. Which of these comprise of the correct species of Nematoda
Hair worm, eel worm, stomach worms
27. Annelids are segmented worms
True
28. Flat worms comprise of three major classes which are
Turbellaria, Cestoda, trematoda
29. Chordates are invertebrates
False
30. Excretory organ of arthropods is
Malpighian tubules
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