Kingdom Animalia: Classification, Characteristics and Examples

Kingdom Animalia:

Animals are eukaryotic, multicellular organisms. Heterotrophic organisms(animals) are include in Animalia. Animalia is come from Latin word anima which means soul. Animals are might be evolved from protoctists. There is vast diversity of organisms in kingdom Animalia, from simple sponges to complex mammals.

General characteristics:

They are motile.
They heterotrophic organisms(depend on other animal and plants for food).
They are multicellular complex organisms.
Their cell are without cell wall.
Their growth and development have very complex stages i.e. embryonic development.
They may be radial symmetry or bilateral symmetry.
They can primarily reproduce sexually and few are asexually.

Classification of animals:

Animals are classified into two groups: Invertebrate and vertebrate.

Invertebrates:

The animals which are without backbone are called invertebrates. They are simple animals. These are some phylum which are include in invertebrate.

Porifera:

Porifera are most primitive animals. Porifera refers to porous bodied animals which are commonly known as sponges. Porifera derived from Latin word porous: pore, ferra: to bear. There are almost 5000 species of sponges, 150 live in freshwater while other live in marine water.

General characteristics:

They are macroscopic animals, having size from few millimeters to one meter.
These are simplest animals and haven't tissues and organs.
There are pores in body wall.
They depend on water currents for food.
They can reproduce both sexually and asexually.
Adult sponges are attached to rock while larvae can swim.
Neuron cells are present for sensation but has no true nervous system:
Some common examples are Spongilla, Sycon and Euplectella.

Cnidaria:

Cnidaria comes from Greek word cnidos which means stinging cells. Cnidarian are names due to special cell cnidocytes. These cells give rise to nemocytes-stinging cells. There are approximately 9000 to 10000 species of cnidarian live in water.

General characteristics:

They have tissues organization and less evolved nervous system.
They excrete their food through diffusion.
They have single opening of excretion and egestion.
They are carnivores and feed on other animals.
They can reproduce by both sexually and asexually.
Many species are live as individuals and some are colonial.
Some common examples are Obelia, Hydra and Actinia.

Platyhelminthes:

`These animals have soft and compressed bodies. Platyhelminths comes from Greek word means "flatworms". There are approximately 20,000 species of flatworms are known. They are further classified into;

Turbellaria: Free living
Monogenea: External parasite
Trematoda: Flux
Cestoda: tapeworm

General characteristics:

Platyhelminths are triploblastic means there is development of third layer mesoderm, which separates the ectoderm and endoderm.
Their body is unsegmented.
They are include in bilateral symmetry.
Their size ranges from few millimeter to several meters.
Some flatworms are parasitic e.g. tapeworm and some are free living such as planaria.
They haven't digestive and circulatory system but have a well developed nervous system. Their nervous system consist of branches of nerves and ganglia.
They have sac type digestive system. Digestive system may be absent or poorly developed.
They can reproduce sexually and sometime asexually.
Some common examples are planarian, tapeworm and liver fulke.

Nematode:

Nematodes comes from Greek word means "pointed end". This phylum include those animals which have worm like cylindrical body and pointed ends. Approximately 25,000 to 30,000 species of nematodes are found.

General characteristics:

Nematodes are pseudocoelomates and triploblastic.
They have no clear head and also don't have special sense organs.
They are bilateral symmetry with unsegmented body.
Their size ranges from micrometers upto one meter.
Their digestive system is in the form of alimentary canal. It has two opening: Anterior opening is mouth and posterior opening is anus.
Locomotion is occur through contraction and relaxation of muscles.
They have special reproductive organs and can be reproduce sexually.
They are parasites or free living.
Some common examples are hookworms, dog heartworm and pinworm.

Annelida:

Annelida comes from Latin word means "little rings". These are named because they have segmented body. Their body is divided into similar little parts or segments. Approximately 17000 to 22000 species of annelida are known to scientists.

General characteristics:

They are bilateral symmetry and triploblastic.
Respiratory system is absent. Gaseous exchange is occur through diffusion.
They are also free living and some are parasitic.
They have closed circulatory system.
Digestive system is in the form of alimentary canal. Anterior end is mouth and posterior end is anus.
They have well developed nervous system with simple brain and ventral nerve cord.
Their skin is moist by mucus and coelomic fluid.
They can reproduce sexually and have separate sexes.
Some common examples are earthworm, nereis and leech.

Arthropoda:

Arthropoda word comes from Greek word Arthro means "joined" and poda mans "feet". These are named because they have joined appendages. This phylum contain 5-10 million species. Insects are most common arthropod known on earth.

General characteristics:

They have bilateral symmetry and triploblastic.
They have segmented bodies and joined appendages.
Their bodies are may be worm-like and other can fly.
They have well developed head, thorax and abdomen.
They have well developed digestive system, circulatory system, respiratory system and highly developed nervous system.
Malapighian tubules are present in excretory system. They excrete uric acid.
Their nervous system consists of simple brain connected to ventral double nerve cord.
They have trachea for gaseous exchange. Aquatic arthropod use gills for respiration.
They have open circulatory system. They have a primitive and blood vessels.
They have exoskeleton which is outer covering of cuticle made of chitin.
They can swim, crawl or fly for locomotion.
They have separate sexes and sex organs. They reproduce sexually.
Some common examples are mite, butterfly, wasp, woodlouse and crab.

Mollusca:

This phylum include diverse group of organisms. It include soft-bodies, triploblastic and sluggish animals. This phylum contain over 50,000 species.

General characteristics:

They are triploblastic coelomates.
They have bilateral symmetry.
They have unsegmented soft bodies.
Mostly possess calcareous(containing large amount of calcium) shells which protect their soft body.
They are widely distributed in freshwater and marine. Some terrestrial live in moist place.
They have highly organized circulatory, excretory, reproductive, digestive and nervous system.
The circulatory system is opened except Cephalopoda. They contain a blue pigment haemocyanin instead of haemoglobin.
Mostly gaseous exchange by gills. In terrestrial environment cavity is converted to lungs.
They have separate sexes.
They have sac like digestive system with two opening mouth and anus.
Their nervous system consist of three ganglia in hand, foot and body regions. These ganglia(a group of cell body) are interconnected.
They have paired nephridia as excretory organ.
The major classes of phylum Mollusca are gastropoda, bivalvia and cephalopoda.

Enchinodermata:

Phylum enchinodermata contains animals have a water vascular system and five-sided radial symmetry. Over 5,000 species of this phylum are known.

General characteristics:

They are triploblastic animals.
Their larva contain bilateral symmetry but their adult have radial symmetry.
They have different body shapes such as flattened like biscuit(cake urchin), globular(sea urchin), star-shaped with short arm(star fish), star-shape with long arm(brittle star) and elongated(sea cucumber).
They have a common ability called regeneration.
they have separate sexes and the fertilization is internal.
They have organized digestive and reproductive system.
But have no specialized excretory and respiratory organs.
Their nervous system is poorly developed.
Common examples are brittle star, crinoids, sea cucumber and blastoid.

Chordata:

The phylum Chordata named because all animals of this phylum possess notochord. More than 60,000 species are known. Mostly are vertebrates. this phylum is further classified into sub-phylum urochordata, cephalochordata and vertebrate.

Urochordata:

They have no cranium. Notochord and nerve cord are only in free-swimming larvae. They are also called tunicates because they are enclosed in a covering called tunic. Some common examples are herdemania, pyrosoma and larvacean.

Cephalochordata:

They also have no cranium. Notochord and nerve chord extend the entire length of the body. Common example is amphioxus.

Vertebrate:

They have cranium and a vertebral column. That is why they are called vertebrates.

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