Classification of Kingdom Animalia: Characteristics and Traits

Kingdom Animalia
Written by Fandy

Kingdom Animalia – Kingdom animalia is a taxonomic classification of organisms that do not have their own cell walls and chloroplasts, so they depend on other organisms for food. Unlike the case with plants, animals do not have chlorophyll, so they cannot carry out photosynthesis to make their own food. Therefore, animals have to find their own food to get energy.

Kingdom animalia is arguably one of the kingdoms that has the most numerous and varied members. More than 1.5 million living animal species have been described—about 1 million of which are insects—but it is estimated that there are more than 7 million animal species in total. Animals range from 8.5 micrometers to 33.6 meters in length and have complex interactions with each other and with their environment, as well as forming elaborate food webs. The study of animals is called zoology.

The object of zoological study includes the structure, function, behavior, and evolutionary processes of animals. The main topics in zoology are comparative anatomy, ethology, animal psychology, molecular biology, ethology, behavioral ecology, evolutionary biology, taxonomy, and paleontology. Meanwhile, someone who studies zoology is called a zoologist.

In general, the animal kingdom is divided into two, namely invertebrate animals (no backbones) and vertebrate animals (backbones). Invertebrate animals are animals that do not have a backbone and their nervous system is located below the digestive tract, while vertebrate animals are animals that can only reproduce through marriage (fertilization of the ovum and spermatozoid into one unit).

Aristotle divided animals into those with blood and those without blood. Carolus Linnaeus created the first hierarchical biological classification for animals in 1758 in his book Systema Naturae , which was expanded by Jean-Baptiste Lamarck into 14 phyla in 1809.

In the late 1800s, Ernst Haeckel divided the animal kingdom into multicellular Metazoa (now a synonym of Animalia) and Protozoa, while single-celled organisms are no longer considered animals. In modern times, animal classification relies on sophisticated techniques, such as molecular phylogenetics, which are effective in demonstrating evolutionary relationships among animal taxa.

Kingdom Animalia

To recognize various animals that belong to the kingdom animalia group, we certainly need to know their characteristics. What are the characteristics? The following is a summary of the characteristics, features, and types of kingdom animalia.


Kingdom Animalia

Edited by Fir0002, Opoterser, DBCLS, TheAlphaWolf, Philippe Guillaume/Creative Commons Attribution-Share Alike 3.0 Unported.

The word “animal” is a loan from Arabic, حيوان (animal) which means animal. The word “animal” is a loan from Sanskrit which means “creature”, while “animal” is an original Malay word.

In English, “animal” is called animal, from the Latin “animalis”, which means “has breath”. In everyday non-formal usage, the word usually refers to animals, not humans. Occasionally, close human relatives such as mammals and other vertebrates are designated in informal use. The biological definition of the word refers to all members of the kingdom animalia, including creatures as diverse as sponges, jellyfish, insects, and humans.

Characteristics of Kingdom Animalia

Kingdom Animalia

Animals are unique in that they have a ball of cells in the early embryo (1) that develops into a hollow ball called a blastula (2) (Pidalka44/Public domain).

Animals have several characteristics that set them apart from other living things. Animals are eukaryotic (have a nuclear membrane) and multicellular, unlike bacteria which are prokaryotic and unlike protists which are eukaryotic, but unicellular. Unlike plants and algae which produce their own nutrients, animals are heterotrophs, meaning they eat organic matter and digest it internally.

With very few exceptions, animals breathe oxygen and respire aerobically. All animals are motile (able to spontaneously move their bodies) during at least part of their life cycle, but some, such as sponges, coral, clams, and barnacles, become sessile later. The blastula is a stage in embryonic development unique to most animals, which allows cells to differentiate into specialized tissues and organs.

Animals are categorized into ecological groups depending on how they obtain or consume organic matter, including carnivores, herbivores, omnivores, detritivores and parasites. Interactions among animals form complex food webs. In carnivorous or omnivorous species, predation is the resource-consumer interaction that occurs when a predator eats another organism (referred to as prey ).

Animals that live near hydrothermal vents and cold seeps on the dark ocean floor are independent of the energy of sunlight. Instead, archaea and bacteria here produce organic matter via chemosynthesis (by oxidizing inorganic compounds such as methane) and form the basis of local food webs.

Characteristics of Kingdom Animalia

1. Can Move

Animals in the kingdom animalia group have a motion system to move animal body parts.

2. Does not have a cell wall

Unlike the case with plants, animal cells do not have a cell wall function like plants which give the impression of being hard or rigid to protect the cell contents inside, but still have the function of a cell membrane. In the absence of this cell wall it supports the animal’s locomotion system, thus enabling it to move actively.

3. Habitats

Animals occupy almost all habitats and microhabitats on Earth, including saltwater, hydrothermal vents, fresh water, hot springs, swamps, forests, grasslands, deserts, air, to the interior of animals, plants, fungi and rocks. However, animals are not very heat tolerant; very few animals can survive constant temperatures above 50 °C (122 °F). Only a few species of animals (mostly nematodes) inhabit the coldest regions of the Antarctic continent.

3. Organ Systems

The animals in the kingdom animalia group have many organ systems. These organ systems have specific functions that are essential for survival. The organ systems consist of the skeletal system, the muscular system, the digestive system, the circulatory system, the reproductive system, the immune system, and hormones.

4. Body shape

Animal body shape is mostly bilaterally symmetrical, whereas primitive animals (simple animals) have asymmetrical bodies. Other animals have a radially symmetrical shape, such as echinoderms. This body shape is adapted from the way they get their food.

Kingdom Animalia

Type of Kingdom Animalia

1. Vertebrates

Guppies are an example of a vertebrate (Jdiemer/Creative Commons Attribution-Share Alike 3.0 Unported).

Vertebrates are a type of animal subphylum of Chordata which includes all animals that have a backbone. Vertebrates are the largest subphylum of Chordata. All types of fish, amphibians, reptiles, birds, and mammals (mammals) can be included in vertebrates, except for eels, ghosts, and sea leeches.

Vertebrates have a muscular system which is made up of multiple pairs of masses, as well as a central nervous system which is usually located within the spine. The respiratory system uses gills or lungs.

The blood of Vertebrate animals consists of blood cells suspended in the plasma, then circulates to the organs of the body. Cellular elements or blood cells of vertebrate animals are divided into three, namely red blood cells, white blood cells, and platelets. Each type of vertebrate animal has a different shape, size, and percentage of red blood cells and white blood cells.

Vertebrates can only reproduce through mating. The mating process is carried out by fertilizing the ovum and spermatozoid into a single unit. Fertilization in vertebrates can occur outside the body or inside the body. Fertilization outside the body is called external fertilization, while fertilization inside the body is called internal fertilization. External fertilization occurs in fish and frogs, while internal fertilization occurs in reptiles, birds and mammals.

Vertebrates have several types of kidneys, including the pronephros, mesonephros, and metanephros. Pronephros kidney type is a type of kidney that develops in the embryo or larval phase. Furthermore, the pronephros kidney is replaced by a mesonephric type of kidney, which is then replaced by a metanephric kidney when the animal has begun to mature. Animals that have this type of kidney are mammals, reptiles, and birds.

2. Invertebrates

Kingdom Animalia

Insects are one example of an invertebrate ( Michael Apel /Creative Commons Attribution-Share Alike 3.0 Unported).

Invertebrates or Invertebrates are types of animals that do not have a backbone between the vertebrae. These invertebrate animals are divided into several groups, namely the phylum Protozoa, Porifera, Arthropoda, Platyhelminthes, Nemathelminthes, Annelida, Coelenterata, Molluscs, and Echinodermata.

Invertebrates is a term expressed by Chevalier de Lamarck to designate animals that do not have a backbone. Invertebrates include all animals except vertebrates (fish, reptiles, amphibians, birds, and mammals). In addition to not having hard internal bones, invertebrates are generally soft-bodied and have a hard exoskeleton to protect their bodies. Examples of invertebrates are insects, jellyfish, hydra, squid and worms. Invertebrates make up about 97% of all members of the animal kingdom.

There are eight phyla in the classification of Invertebrates, namely:

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  • Annelids.
  • Arthropods.
  • Coelenterata.
  • Echinodermata.
  • Mollusca.
  • Nemathelminthes.
  • Platyhelminthes.
  • Porifera.

Further research in the field of taxonomy showed that many invertebrate animals are more closely related to vertebrates than to other invertebrates.

The formation of a new individual in invertebrate sexual reproduction does not always require and undergoes a fertilization process. Reproduction without fertilization is called parthenogenesis which can occur in male bees and male ants.

The reproduction by fertilization is divided into two, namely conjugation and anisogamy. An example of an invertebrate whose reproductive organs are not yet clearly conjugated is paramecium. Anisogamy on the other hand is the fusion of two sex cells that are not the same size. Anisogamy, for example, occurs when microgametes and macrogametes fertilize in plasmodium, as well as sperm fertilize with ovum in the uterus.

Diversity of Kingdom Animalia

1. Biggest and Smallest

Kingdom Animalia

A blue whale in the Azores (Frank Wirth/Creative Commons Attribution-Share Alike 3.0 Unported).

The blue whale ( Balaenoptera musculus ) is the largest animal that ever lived, weighing up to 190 metric tons and up to 33.6 meters (110 ft) long. As the name suggests, the blue whale has a predominantly dark blue body with a slightly paler color on the underside. There are at least three subspecies of the blue whale, namely B. m. musculus in the North Atlantic and North Pacific, B. m. intermedia in the Southern Ocean, and B. m. brevicauda (also called the pygmy blue whale) in the Indian Ocean and South Pacific Ocean.

Prior to whaling, the largest population was in Antarctica, numbering approximately 239,000 (between 202,000 and 311,000).These whales can reach speeds of 50 kilometers per hour (31 mph) (usually when interacting with other whales), but their usual speed is only 20 kilometers per hour (12 mph). When feeding, the speed reduces to 5 kilometers per hour (3.1 mph).

The staple food of blue whales is krill, although they also eat small amounts of copepods. This species of zooplankton is eaten by various blue whales from one ocean to another. An adult blue whale can eat up to 40 million krill per day. They always feed in areas with the highest concentration of krill, sometimes consuming as much as 3,600 kilograms (7,900 pounds) of krill in a single day. The energy requirement of an adult blue whale in one day is in the range of 1.5 million kilocalories.

The largest extant land animal is the African bush elephant ( Loxodonta africana ), weighing up to 12.25 tons and up to 10.67 meters (35.0 ft) long. The largest land animals that have ever lived were titanosaur sauropod dinosaurs such as Argentinosaurus , which may have weighed up to 73 tons. Some animals are microscopic; some Myxozoa (obligatory parasites belonging to the group Cnidaria) never grow larger than 20 µm, and one of the smallest species ( Myxobolus shekel ) does no more than 8.5 µm when fully grown.

Also Read: ” Unique Facts of the 7 Largest Whale Species in the World “.

2. Reproduction and Growth

Sexual reproduction occurs in almost all animals, such as these dragonflies (Simptonym/Creative Commons Attribution-Share Alike 4.0 International).

Nearly all animals use some form of sexual reproduction. Animals produce haploid gametes via meiosis; the smaller, motile gamete is the spermatozoa and the larger, non-motile gamete is the ovum. Spermatozoa and ovum unite to form a zygote, which develops by mitosis into a hollow ball called a blastula.

Within a sponge, the blastula larva swims to a new location, attaches to the seafloor, and develops into a new sponge. In most other groups, the blastula undergoes more complicated rearrangements. The blastula undergoes invagination (a certain folding) to form a gastrula which has a digestive chamber and two separate germ layers, namely the external ectoderm and internal endoderm. In many animals, a third germ layer, the mesoderm, also develops in between. These germ layers then differentiate to form tissues and organs.

The Origins of Evolution

Kingdom Animalia

Dickinsonia costata of the Ediacaran biota, (c. 635–542 million years ago) is one of the earliest known animal species ( Verisimilus /Creative Commons Attribution-Share Alike 3.0 Unported).

The first fossils that may represent animals have appeared in 665 million year old rocks in South Australia’s Trezona Formation. These fossils are interpreted as early sponges. The oldest animals were found in the Ediacaran biota towards the end of the Precambrian, around 610 million years ago. The discovery of cholesterol animal lipids in the Dickinsonia fossils is evidence that the Ediakara biota is a type of animal.

Most animal phyla first appear in the fossil record during the Cambrian explosion which began about 542 million years ago in places such as the Burgess Shale. Extant phyla that can be found in these rocks are Molluscs, Brachiopods, Onychophora, Tardigrada, Arthropoda, Echinodermata, and Hemichordata.

Some paleontologists suggest that animals appeared much earlier than the Cambrian explosion, perhaps 1 billion years ago. Trace fossils such as tracks and burrows from the Tonian period indicate the presence of triploblastic worm-like animals, approximately about 5 mm in size. However, similar tracks produced by the giant single-celled protist Gromia sphaerica do not indicate the early evolution of early animals.