Animal Classification

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Animals are classified into two main groups, Invertebrates and Vertebrates.  have a backbone, while vertebrates (Humans, birds and mammals) do. The animal kingdom is further divided into 20 phyla, of which the following are of agricultural importance: 

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Phylum Protozoa

This phylum consists of unicellular free-living animals (one cell). Most of them live in water, either seawater, fresh water or soil borne water. They are nearly all microscopic.

The various species of Protozoans move in a number of ways:

  • Pseudopodia (False feet)

  • Cilia (Small moving hairs)

  • Tails

Reproduction of protozoans occurs by means of binary fission or mitosis. Amoeba is one of the most common protozoans and moves by means of pseudopodia. To see a video of the Amoeba click here! One of the most agriculturally important species of Protozoans is Babesia.

This protozoan causes Red-water fever, a disease that affects 100,000 cattle a year.

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Phylum Platyhelminthes

The phylum literally means “flat worms” and all the members of this phylum are flat worms! The phylum is classified into three main groups or classes:

  • Class Turbellaria (Free living)

  • Class Trematoda (Parasitic Flukes)

  • Class Cestoda (Parasitic Tapeworms)

TapewormsAll platyhelminths are hermaphrodites (are both male and female) and can, if required, can fertilize themselves. The most important agricultural species of platyhelminths is the Liver Fluke or Fasciola hepatica. Liver FlukeThe 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). 

The Lifecycle of the 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 pass in the faeces and hatch two weeks later in water and form a ciliated Miracidium. 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 becomes encysted (forms a shell) 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. Click here for information on the Liver Fluke's life cycle!


Life cycle of the liver fluke.

Understanding the lifecycle of the liver fluke allows us control the spread in the following ways:

  • Dosing any animals to kill the adult fluke

  • Spraying molluscicides to kill the snail.

  • Draining land (the snail only lives in water)

  • Fencing flooded areas

  • Don’t graze wet lands after August

For teagasc guidelines for the control of Liver Fluke, click here : 

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Phylum Nematoda

Nematodes are also known as roundworms or eelworms. There are huge numbers of species in this phylum. All theseNematode 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

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Phylum Annelida

These are the segmented worms and include the earthworm – Lumbricus terrestris and leeches. On each segment, earthworms have four bristles or Chaetae, which they use to move. Earthworms are important to the farmer because they improve the soil in the following ways:

  • They eat their way through the soil and mix the ingested material with mucus in their guts. This helps to improve soil crumb structure.

  • Depositing soil in different places and mixing horizons.

  • Improve drainage of heavy clay soils

  • Introduces more air into the soil.

  • When they die the further increase the amount of organic matter.

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Phylum Mollusca

The molluscs include slugs, snails, squid, mussels, clams and octopus. These animals generally have a foot, which excretes a slimy mucus. They also have a rasping tongue. The most agriculturally important mollusc is the mud snail (Lymnaea truncatula)

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Phylum Arthropoda

This is the largest phylum containing nearly a million species. Therefore it is necessary to sub classify the phylum into classes. All Arthropods have jointed legs and an exoskeleton (outer skeleton). Members of the phylum include scorpions, insects, spiders, shellfish (crustaceans), woodlice, centipedes and millipedes.

The most important classes of Arthropods are the spiders and insects.

Class Insecta (Insects)

They have three main body parts: Head, thorax and abdomen They include aphids, lice, fleas, crane-flies and butterflies.

The life cycle of all insects follows this path:

Egg       -       Larvae       -         Pupa       -      Adult


Class Arachnida (Spiders)

The spider has two main body segments, the cephalothorax and the abdomen. Some of the diseases spiders cause on the farm are mange (scabies) and flea (mites). Ticks are blood sucking spiders that can attack sheep and spread disease (red water fever)

A lot of the members of phylum Arthropoda are Parasites.

Parasites are animals that live at the expense of other animals.


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Phylum Chordata

All animals in the phylum Chordata have backbones and are vertebrates. Examples include fish, birds, amphibians, reptiles and mammals. The two main agricultural classes are Class Aves (Birds) and Class Mammalia (Mammals).

Only these two classes are said to be homoeothermic – warm blooded – and can regulate their body temperature.

Class Aves

All members of this class have feathers, no teeth but a beak, lightened bones and no bladder.

Class Mammalia

All mammals have the following traits:

  • Hair

  • A Placenta

  • Mammary glands to produce milk

Again they are further classified into sub classes. Some of the common sub classes are:

  • Carnivores (Dogs and cats)

  • Ungulates (Hooved animals)

  • Odd toed - horse

  • Even toed – sheep, cattle

  • Marsupials – kangaroos

  • Primates – monkeys and humans

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Which Phylum do they belong to ? - Click here to take the quiz!

More links of Animal Classification and Taxonomy

Animal Diversity Web

The Animal Kingdom

Animal Families

Taxonomy 101

The ABC’s of Taxonomy

Animal Classification Game!

Test Your Knowledge of This Page with a Crossword

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[ Animal Classification ] Food and Feeding ] The Digestive System ] The Breathing System ] The Circulatory System ] The Lymphatic System ] The Nervous System ] The Endocrine System ] The Reproductive System ] The Skeletal System ]



Leaving Certificate Agricultural Science