What is Animal Diversity?

The animal world is large and diversified based on its members' shape, size, eating habit, habitat, method of reproduction. Animals show variations in their anatomy, physiology, and genetic features. Based on those differences, they are put into different categories. This diversification takes place due to the adaptation of each animal species to its surrounding environment. Animal diversity is also mentioned as “biodiversity”.

Types of Biodiversity

Biodiversity is generally divisible into three types-

  • Genetic diversity: It refers to the diversity of the genetic characteristics within a species. Genetic variation enables natural selection, depending upon the genetic information the animals share. The more characteristics they share, the more similar they appear.
  • Species diversity: This diversity exists within a habitat or a region. The term 'Species richness' indicates the total number of species in a particular geographical region.
  • Ecological diversity: It is an intricate connection between various types of species of the local ecosystem and the dynamic interplay between them. The ecosystem consists of organisms from different species that stay together in an area and their relationship builds up with the abiotic and biotic factors.

Importance of Diversity

The evolution of animals began over 600 million years ago. The organism that existed then, may not exist in the present time and probably do not resemble any living creature today. From that time, animals have evolved in a highly diverse kingdoms. Researchers have identified over one million species that exist on Earth. Animals vary in complexity as they exist in a form of a simple to most complex being. Scientists face difficulties in classifying them in a group. They should point out the traits, common to all creatures, and the traits that can discriminate the dissimilarities among interconnected groups of organisms. The classification system differentiates the animals as per their superficial structure, morphology, evolutionary data, development at the embryo stage, and genetic features. It is a continuous process as the new species discovery is actively going on. It also helps to understand the procedure of conservation of the diversity of life on the Earth.

Purpose of learning Animal Diversity

Animal diversity web or ADW is a non-profiled site regarded as an online database of animal’s natural history, distribution, classification, and conservation. Thousands of students and informal visitors utilize this site to answer questions. It is a science-learning tool or query tool along with a facility of a virtual animal museum. It is studied to motivate and guide the student observation of animal and plant similarities and dissimilarities with their adaptation to living in a specific environment.

Measurement of Diversity

Several 'objectives' of measurement have been applied to estimate biodiversity from field observations. The primary idea of the 'biodiversity index (the scale of diversity of a particular species in area 'X')' is to calculate a quantity of variability in space or in time that can be utilized for the comparison among biological entities, made up of distinct components. The indices are as follows

Species richness indices

The calculation of the total number of species present in a community is species richness. Although, the overall intervention of all species that exist in a certain region is almost an unattainable goal in some applications.

Evenness indices

This measurement explains the evenness in the allocation of each and everyone in a community among different species.

Taxonomic indices

It considers the taxonomic relationships between separate organisms in a community. It helps in classifying the taxonomic distance found between two organisms. They are chosen at unplanned places. These are found in three manners and utilized on different spatial scales-

  • Alpha diversity: It is studied as the diversity within a specific locality, community, or ecosystem. It is estimated through the counting of the number of taxa within the ecosystem.
  • Beta diversity: This refers to the species diversity that takes place within multiple ecosystems. It involves the comparison of the number of taxa, which is exclusive to each of the ecological systems.
  • Gamma diversity: This is the measurement of overall dissimilarities of separate ecosystems within a specified region.

Useful features to classify the animals

All animals are multicellular and eukaryotic organisms. Most of them exhibit complex tissue structures with modified and specialized tissue. They are also known as heterotrophs. They take help from other organisms to gain energy. Almost everyone cannot prepare their food. They can be carnivores (flesh-eater), herbivores (plant-eaters), omnivores (eat both flesh and greens), or parasites (take nutrition from other animals by affecting the host). Three constituents are very significant in determining the animals; body plan, feeding habit, and extant or not. Body plan is the summation of the morphological features among several members of a phylum-level group. Feeding habit is the proof of resources used as an energy supplier.

The pattern of classification

In biology, the diversity in kingdom Animalia has expressed the classification of 36 distinct  animal phyla based on their evolutionary context. The most significant seven phyla are Porifera, Cnidaria, Platyhelminthes, Annelida, Mollusca, Arthropoda, and Chordata. The first six phyla are invertebrates. They do not possess a notochord in their body.


It is the earliest and most simple phylum. It involves the multicellular, asymmetrical, filter-feeding sponge-type creatures, which lack distinct tissue layers. They can regenerate even after getting broken to the level of a single cell. The adults are mostly sedentary, which means they fail to move from one place to another. Parazoa is a subdivision of phylum Porifera in which there is a loose connection between cells and the structure behave as an aggregation of cells rather than a multicellular organism. Sponges are the most common parazoa.

A sponge found in the ocean. It belongs to the phylum Porifera.
CC BY-SA-3.0 | Image Credits: https://commons.wikimedia.org | Peter Southwood


This phylum has animals such as jellyfishes and coral. They display radial symmetry in their body plan and exhibit diploblastic structure. Diploblastic refers to the two layers of tissues. These layers are ectoderm (outer body layer) and endoderm (inner body layer). They also consist of a simple gut-like growth with a single opening for food intaking and waste discharge. Adult Cnidarians are mostly sedentary like the phylum Porifera.

Sea Nettle belongs to the phylum Cnidaria
CC BY-SA 4.0 | Image Credits: https://commons.wikimedia.org | Defi22


These are worm-like creatures. They breathe, with the aid of gaseous exchange, through their skin. They generally live in moist or aquatic environments. It includes  animals such as flatworms and trematodes, which are free-living or parasitic. They have an additional tissue layer called mesoderm between ectoderm and endoderm, so they are considered 'triploblastic'. They display bilateral symmetry, which means that their body can be divided in half along a plane.

Hammer-headed worm belongs to the phylum Platyhelminthes
CC BY-SA 4.0 | Image Credits: https://commons.wikimedia.org | Mohammed Rafiq


Nematodes are commonly known as roundworms. They are free-living, very tiny organisms. They have an elongated and tubular body. These organisms have a nervous system and are mostly act as parasites to both animals and plants.


Structurally, this phylum is quite similar to the Platyhelminthes. Earthworms, leeches are some examples. They have a body cavity called “coelom”. It is located between the gut and the body wall. They display a certain body plan called metamerism. All body parts are segmented in a compartmentalized way in this unique invertebrate. Each compartment can function individually. It is a significant character for the progressive evolutionary change. It is accepted as “division of labor”. They have separate locomotory appendages.

Segmented worm belongs to the phylum Annelida
CC-BY-SA-4.0 | Image Credits: https://commons.wikimedia.org | Ryan Hodnett


This phylum is full of anatomically diverse organisms. Some prominent creatures of this phylum are Octopuses, snails, and clams. All molluscs have a mantle, a protective covering for their soft body organs like respiratory organs, alimentary or epithelial duct, and reproductive parts.

Octopus that belongs to phylum Mollusca
CC-PD-Mark 1.0 | Image Credits: https://commons.wikimedia.org | Comingio Merculiano


Phylum Arthropoda is the most diverse phylum in the whole animal kingdom. This phylum occupies around three-quarters of all current and extinct species discovered. All members have a hard, chitin-based coating, which is mentioned as an exoskeleton. Their body is divisible into the distinct head, thorax, and abdomen regions. Most of them contain specialized sense organs. Spiders, butterflies, crabs, scorpions, prawns, and some organisms belong to the phylum Arthropoda.

A Scorpion that belongs to the phylum Arthropoda
CC BY-SA 4.0 | Image Credits: https://commons.wikimedia.org | Vijayakumarblathur


Higher categories of organisms are placed in this phylum. They are also called vertebrates or chordates because of the notochord or nerve chord. It is assessed as the most crucial feature of their nervous system. It is a diversified group containing tunicates, fish, reptiles, amphibians, aves, and mammals.


The diversification in living organisms is essential for maintaining the ecosystem. Species depend on each other for their survival. The carbon and nitrogen cycle are maintained in an environment with the assistance of plants, bacteria, animals, and all other abiotic factors. Several organisms like birds, bees carry forward the reproduction and diversity of plant species and eventually help in oxygen replenishment in the atmosphere. The food chain system also helps in the growth of several organisms while controlling the development of some organisms.

Context and Applications

Students can gain knowledge on this context in two main fields of biology and can pursue further studies. The streams are

  • Ecology
  • Zoology

Practice Problems

  1. From which phylum true Coelom has originated?
    1.  Platyhelminthes
    2. Arachnida
    3. Annelida
    4. Amoeba

Correct Answer: c. Annelida

2. What does "Species Richness" indicate?

  1. More species in a growing community.
  2. A total number of species in a single community.
  3. The total number of species in two neighboring communities.
  4. A lower number of species in a single community.

     Correct Answer: b. A total number of species in a single community

      3. Which is the most diverse phylum among all invertebrates?

  1. Annelida
  2. Mollusca
  3. Protozoa
  4. Arthropoda

Correct Answer: d. Arthropoda

      4. Which animal possesses nematocyte as a protecting organ?

  1. Sea anemone
  2. Hydra
  3. Octopus
  4. Polychaete

Correct Answer: a. Sea anemone

      5. To which phylum do Land snails belong?

  1. Annelida
  2. Chordata
  3. Mollusca
  4. Cnidaria

Correct Answer: c. Mollusca

Common Mistakes

Students often forget to study invertebrates and focus on mammals only while studying animal diversity. The animal kingdom is a very diverse and vast, and it displays significant diversification in lower animals as well. It is mandatory to focus on learning about all groups.

Animal diversity is a major part of biology. It is related to-

  •         Genetic evolution
  •         Animal taxonomy
  •         Ecosystem

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