Kingdom Animalia

There are millions of animal species in the Kingdom Animalia, and studying them without a basic classification can be confusing. Aside from that, several new animal species are constantly being discovered. Identification, naming, and assigning a systematic position to newly discovered species all require classification. 

The Animal Kingdom is classified primarily based on the similarity of its characteristic features. The Animalia is made up of are eukaryotic, multicellular, the heterotrophic organisms. They consist of approximately 35 phyla, 11 of which are considered major phyla. Invertebrates, or animals without a backbone, account for nearly 99 percent of all animals. The rests are vertebrates or animals with backbones. Animals are divided into two major groups based on the presence or absence of a notochord (vertebral column), which are nonchordates and chordates.

Definition

The Kingdom Animalia is a diverse group of eukaryotic, multicellular organisms that are heterotrophic. As a result, they get their nutrition from outside sources. Animal cells lack a cell wall, which is present in plant cells, even though they are unable to produce their food, which is one of the main distinguishing features of plants. Except for a few animals, the majority of animals are motile, allowing them to respond to stimuli and find food, among other things. 

In general, animals are classified into two groups: vertebrates (animals with a backbone) and invertebrates (animals without a backbone) (animals that lack a backbone). They are, however, divided into several phyla.

Animal reproduction and development

Most animals have diploid body (somatic) cells and a few haploid reproductive (gamete) cells produced by meiosis. There are some exceptions: In bees, wasps, and ants, for example, the male is haploid because it develops from an unfertilized egg. Most animals reproduce sexually, but many also have asexual reproduction mechanisms.

Sexual reproduction and Embryonic development

Almost all animal species are capable of sexual reproduction; for many, this is the only mode of reproduction available. This distinguishes animals from fungi, protists, and bacteria, all of which reproduce asexually. During sexual reproduction, a species’ male and female gametes combine in a process known as fertilisation. 

The small, motile male sperm usually travels to the much larger, sessile female egg. Sperm comes in a variety of forms, including cells with flagella or amoeboid cells to aid motility. A zygote is formed by the fertilisation and fusion of the gamete nuclei. Fertilization can be internal, as in many land animals, or external, as in many aquatic species.

Classification features of animals

Animals are classified based on morphological and developmental traits such as body plan. The animal body plan is symmetrical, except for sponges. This means that their body part distribution is balanced along an axis. The number of tissue layers formed during development, the presence or absence of an internal body cavity, and other embryological development features all contribute to animal classification.

Asexual reproduction

In contrast to sexual reproduction, asexual reproduction produces offspring who are genetically identical to each other and the parent. Asexual reproduction is possible in a variety of animal species, most notably those without backbones, but also in some fish, amphibians, and reptiles. Asexual reproduction is absent in birds and mammals, except for the occasional identical twinning. 

Budding and fragmentation are the most common forms of asexual reproduction for stationary aquatic animals, in which a portion of a parent individual can separate and grow into a new individual. Parthenogenesis (or “virgin beginning”) is a type of asexual reproduction found in certain invertebrates and rare vertebrates, in which unfertilized eggs develop into new offspring.

Complex tissue structure

Animals have specialised structures that are differentiated to perform specific functions. Most animals, like multicellular organisms, develop specialised cells that group together to form tissues with specialised functions. 

A tissue is a grouping of similar cells that share an embryonic origin. Animal tissues are classified into four types: nervous, muscle, connective, and epithelial. Neurons, or nerve cells, are found in nervous tissue and are responsible for transmitting nerve impulses. Muscle tissue contracts to produce all types of body movement, from organism locomotion to movements within the body itself.

Animals have specialised connective tissues that perform a variety of functions, including transport and structural support. Blood and bone are examples of connective tissues. Connective tissue is made up of cells separated by extracellular material composed of organic and inorganic materials, such as bone protein and mineral deposits. 

Epithelial tissue covers the internal and external surfaces of organs within the animal body, as well as the external surface of the organism’s body.

Conclusion

There are millions of animal species in the Kingdom Animalia, and studying them without a basic classification can be confusing. The Animalia is made up of are eukaryotic, multicellular, the heterotrophic organisms. Animals are divided into two major groups based on the presence or absence of a notochord, which are nonchordates and chordates. The Kingdom Animalia is a diverse group of eukaryotic, multicellular organisms that are heterotrophic. Animal cells lack a cell wall, which is present in plant cells, even though they are unable to produce their food, which is one of the main distinguishing features of plants. Except for a few animals, the majority of animals are motile, allowing them to respond to stimuli and find food, among other things.