Did you know that there are over 1 million known species of animals on our planet, ranging from tiny insects to enormous elephants?
One of the ways scientists classify these animals is by dividing them into different groups based on their characteristics.
Today, we will dive into the animal kingdom and explore the fascinating world of phylum and subphylum.
Get ready to discover the incredible diversity of animal life and how scientists organise it all!
Introduction: Animal Kingdom Classification
Based on cell structure, manner of reproduction, source of sustenance, and physical characteristics, R.H. Whittaker divided living things into five kingdoms. Whittaker suggests the following kingdoms: Monera, Protista, Fungi, Plantae, and Animalia.
Some of the most advanced and sophisticated species are in the animal kingdom.
Multicellular heterotrophic organisms with animals are formed from embryonic layers. There are thought to be 8.7 million animal species! Over 2 million of them have been correctly identified and categorised by scientists. All animals are included in the largest of the five kingdoms, Kingdom Animalia.
Kingdom Animalia
On Earth, there are about two million different species of animals, and ten thousand new ones are discovered every year. They have been divided into ten major phyla, of which nine are invertebrate phyla (animals without a backbone). The five more classes that comprise the one phylum of vertebrates—animals with a backbone—include mammals, birds, fish, reptiles, and amphibians.
Every animal is part of Kingdom Animalia. Animals are multicellular eukaryotes that get their energy by consuming other living things. Plants have cell walls and chloroplasts, which separate them from animals. The capacity for movement sets animals apart from other eukaryotes.
Here is a list of the different phyla used to classify animals:
- Phylum Porifera
- Phylum Coelenterata
- Phylum Platyhelminthes
- Phylum Nematoda
- Phylum Annelida
- Phylum Arthropoda
- Phylum Mollusca
- Phylum Echinodermata
- Phylum Hemichordata
- Phylum Vertebrata
Porifera (Sponges)
Porifera, often known as sponges, are characterised by having holes in their bodies. The main characteristics of Porifera are
- The organisation of cells is diploblastic, lacks a plane of symmetry, and has random body forms.
- Non-moving multicellular creatures with a hard external skeleton.
- Possesses a porous body.
- To ensure an ongoing supply of water, many canals are present.
- There is a calcareous/silica internal skeleton present.
- Sequential hermaphrodites.
- Examples of poriferans include Spongilla, Sycon, and Euspongia.
Coelenterata (Cnidaria)
- Diploplastic, acoelomate, and radially symmetrical and tissue-level organisation.
- The digestive system is not complete. A single aperture that serves as the mouth and anus lead to a central gastrovascular cavity (coelenteron), which is exposed to the outside.
- There are two forms: the polyp and the medusa. The medusa is shaped like an umbrella and mostly free-swimming, whereas poly is cylindrical and mostly stationary. In both types, tentacles extend from the mouth.
- Nematocyst, a deadly, stinging thread, is found in cnidoblast.
- Examples− Hydra, Adamsia (Sea Anemone), Physalia (Portuguese Man-o-War), Jellyfish etc.
Platyhelminthes (Flatworms)
- Aquatic species.
- Bilateral symmetry, triploblastic, acoelomates, organ system level of organisation.
- Body that is flattened dorso-ventrally.
- No segmentation on the body.
- Platyhelminthes are parasites of the human body. Hooks and suckers are specialised organs found on tapeworms.
- They do not have a true internal cavity.
- Examples of some flatworms are − Dugesia (Planarians), Schistosoma (blood fluke), Fasciola (liver fluke), Taenia (tapeworms), etc.
Nematoda (Aschelminthes)
- Found both in aquatic and soil habitats.
- Pseudocoelomates, triploblastic, and bilaterally symmetric.
- Unsegmented roundworms with tapering ends.
- Cuticles are present on the body wall.
- Many organisms live inside humans and other higher animals as parasites.
- Example: Ascaris and Wuchereria
Annelida
- True coelomates, the triploblastic organisation at the organ-system level, and bilateral symmetry.
- Worms with metameric segments.
- This phylum gets its name from grooves that resemble rings and are termed annuli. The same organs make up each segment/annulus.
- Most species have bristles or setae.
- Well-developed excretory system of nephridia present in annelids for excretion and osmoregulation.
- Examples− Nereis, Pheretima, Hirudinaria (leech).
Arthropoda
- With more than one million species, or over 84% of all animal species, this phylum is the biggest and most successful in the animal kingdom.
- True coelomates, triploblastic, bilateral symmetry, and organ-system level of organisation.
- Segmented metamerizically.
- The body is divisible into the cephalothorax and the abdomen or the head, the thorax and the abdomen.
- There are joined and paired appendages.
- Malpighian tubules function as an osmoregulatory and excretory system.
- Sexes are distinct, and internal fertilisation is mainly seen.
- Examples include insects (honey bee, silkworm, etc.), crustaceans (crabs, lobsters), arachnids (scorpions, spiders, etc.), and centipedes and millipedes.
Mollusca
- It is the second-largest group in the animal kingdom, with approximately 100,000 species.
- Bilateral symmetry, triploblastic coelomates, organ-system level of body organisation.
- Mantles are often used to shield the soft body.
- Head, muscular foot, and visceral hump on an unsegmented body.
- There is a separate feeding organ called a radula.
- While having some terrestrial varieties, they are primarily marine in nature.
- Examples include Chaetopleura, Dentalium, Sepia, Octopus, Pila, and Sepia.
Echinodermata
- Exclusively marine, spiny-skinned benthic creatures.
- Organization at the organ-system level, triploblastic and coelomic, is radially symmetrical.
- It has a distinctive water vascular (ambulacral) system consisting of tube feet that serve as a water filter and feeding and attachment functions.
- There is an interior calcareous skeleton.
- Specialized podocytes for ultrafiltration coupled to the madreporite opening make up the excretory system.
- Sea cucumber, starfish, sea lily, brittle star and sea urchin are a few examples.
Hemichordata
- These are not actual chordates.
- Worm-like creatures that are only marine.
- Bilateral symmetry, triploblastic, true coelomates, and organ system level of body organisation.
- An anterior proboscis, a collar, and a posterior trunk can be found on soft, unsegmented bodies.
- Respiration occurs with the help of gill slits as they are marine.
- Balanoglossus, Saccoglossus, Rhabospleura, Protoglossus, etc., are a few examples.
Chordata
- True coelomates, a triploblastic organisation at the level of the organ system, and bilateral symmetry.
- The existence of pharyngeal gill slits, a post-anal tail, a dorsal and hollow nerve cord, and a genuine notochord at some point in the life cycle.
- There are more than 60,000 species distributed across three subphyla: the Urochordata (Tunicata), the Cephalochordata (Acrania), and the Vertebrata.
1.  Urochordata
Because the adult body is enclosed by a leathery test or tunic made of a cellulose-like organic substance called tunicin, this subphylum is also known as the Tunicata. The notochord is only found in the larva’s tail. In an adult, a dorsal ganglion displaces it.
2.  Cephalochordata
The name of this subphylum comes from the notochord, which reaches up to the anterior end of the body. The notochord remains throughout life.
3.  Vertebrata or Craniata
The notochord is present during embryonic development. In adult forms, the vertebral column (backbone) replaces it. Appendages that are coupled are never more than two pairs. Cephalisation, or the formation of the head, is evident.
There are five different classes within the Phylum Vertebrata.
- Pisces
- Amphibia
- Reptilia
- Aves
- Mammalia
Frequently Asked Questions (FAQs)
Q1: What is the function of the choanocytes in Porifera?
Answer: These cells help maintain a steady current of water and also help capture food and remove wastes from their body.
Q2: Do coelenterates exist only as a ploy or a medusa form?
Answer: Coelenterates can be either a polyp or a medusa, or they can be both. Because the poly and the medusa alternately appear in the same animal, the latter event is known as the alternation of generation.
Q3: What exactly is a pseudocoelom?
Answer: Pseudocoelom is a bodily cavity with patches of mesoderm rather than the entire cavity being lined with it.
Q4: What distinguishes chordates from other animals?
Answer: Chordates are distinct from other animals due to the notochord, hollow nerve chord, gill slits, and other features.
