Characteristics of different phyla of kingdom animalia part II

Are you looking for the characteristics of different phyla of kingdom animalia? In this article you will find the characteristics of phylum annelida, phylum mollusca, phylum arthropoda and phylum echinodermata. To know the characteristics of these phyla, please read this article.


Kingdom animalia is divided into porifera, coelenterata, platyhelminthes, nematoda, annelida, mollusca, arthropoda, echinodermata, hemichordata and chordata . You have read he characteristics of porifera, coelenterata, platyhelminthes and nematoda in my previous article . In this article I will explain the characteristics of other phyla of kingdom animalia.

Characteristics of phylum Annelida

Annelids are commonly known as the segmented worms. The term annelida was proposed by Lamarck in 1801. About 9,000 species of segmented worms are known to us. Annelids are mostly aquatic, marine as well as live in freshwater. The main characteristics of sponges are as follows:

  • Animals or worms of annelida phylum are found in moist soil or water. Some of them live in burrows and some others are parasites.

  • The body is bilaterally symmetrical, metamerically segmented, triploblastic and coelmomate.

  • From outside, body is covered by a cuticle. Below cuticle, there is epidermis. It is followed internally by longitudinal muscular layer.

  • Body is highly contractile.

  • Sometimes lateral appendages in the form of tiny setae are present. But satae are unsegemented. Setae are embedded in the skin and help in locomotion.

  • True coelom is present which is schizocoelous.

  • Alimentary canal is in the form of a tube. Alimentary canal is straight and leads from mouth to anus.

  • Digestion is extracellular.

  • Circulatory system is closed consisting of vessels and tubular heart.

  • Blood is red due to presence of haemoglobin.

  • The excretory system consists of nephridia which are metamerically repeated special coiled ectodermal tubes. Nephridia may open into alimentary canal or directly to out side.

  • Respiration takes place through general body surface or through special projections i. e. gills or parapodia and head.

  • In the nervous system, there is a paired cerebral ganglion or brain and a ventral double nerve cord with ganglia and nerves in each segment of the body.

  • Animals are unisexual or hermaphrodite.

  • Larvae may or may not be present. If present, larvae are trocphophore.

  • some animals are reproduced by budding and some other have the power of regeneration.

Common examples of annelida are Neris, Pheretima (earthworm), Hirudinaria, Arenicola, etc.

Characteristics of phylum Mollusca

The mollusca are soft bodied, non metameric, triploblatic coelomate animals consisting of anterior head, a ventral muscular foot and dorsal mass surrounded by a thin fleshy envelope. The mantle generally sheltered in an external calcareous shell of their own secretion. The term, mollusca was proposed by Johnson. About 1,00,000 species of molluscs are known. Mollusca is the second largest animal phyum after arthropods. The branch of biology deals with the study of molluscs is known as malacology or conchology. The main characteristics of mollusca are given below:

  • Body is covered with a soft skin called mantless.

  • The mantle secretes a calcareous shell which is found outside the body.

  • The body is generally divided into head, foot, mantle and visceral mass.

  • Animals are triploblastic without segmentation.

  • Body is bilaterally symmetrical, however in many animal body is asymmetrical and coiled due to torsion.

  • The body cavity is haemocoel. True coelom is reduced and confined to the pericardial, nephridial and reproductive cavities.

  • Respiratory system is made up of gills, ctenidia, mantle or epidermis. Respiratory pigment is usually haemocyanin.

  • Alimentary canal is complete. Redula is found for chewing food. Digestive glands are in the form of hepatopancreas.

  • Circulatory system is of open type except cephalopods which show some tendency towards a closed system. The blood is colourless, red, blue or green. Heart is covered with pericardium.

  • Excretory system consists of one or two pairs of sac like nephridia or metanephridia which communicate with coelom and also with exterior.

  • Nervous system is made up of paired ganglion and connecting nerves.

  • Animals are mostly unisexual, sometimes bisexual.

  • Development is indirect or direct with metamorphosis.

The common examples of Molluscs are Pila, Neopilina, Chiton, Turbinella, unio, Pinctada, Sepia, Loligo, Octopus, etc.

Characteristics of phylum arthropoda

Arthropodes are metamerically segmented coelomate and jointed limb animals, with a thick exoskeleton containing chitin, molting periodically and without true nephrida and cilia in their structure. Artrhopoda is regarded as the most successful and largest group of animals. Arthropoda has about 9,00,000 species out of which 7,50,000species are the members of class insect. The term arthropoda was proposed by Von Seibold in 1845.The main characteristics of arthropods are:

  • Animals of this phylum are cosmopolitan and found everywhere in air, water and on earth.

  • The body is bilaterally sysmmetrical, triploblastic and metamerically segmented.

  • Arthropod has organ system level of body organization.

  • Jointed and lateral appendages are found which may be modified variously into jaws, gills and legs, etc.

  • Body is covered with exoskeleton which is made up of chitin. It is periodically removed from the body.

  • Body is divided into head, thorax and abdomen. Sometimes cephalothorax is formed due to fusion of head and thorax.

  • the body cavity is haemocoel. The true coelom is greatly reduced in adults. Haemocoel is filled with blood.

  • muscle system is well developed.

  • Circulatory system is of open type and made up of dorsal heart, arteries and blood filled spaces i.e. sinuses.

  • Respiratory system consists of gills, tracheae or booklungs.

  • Alimentary canal runs from mouth to anus. Mouth parts are adopted for various feeding habit.

  • Excretory system is made up of malpighian tubules, green glands or nephridia.

  • Arthropods have simple or compound eye. The later is made of many units called Ommatidia. These have separate lenses and therefore, several images are formed by compound eye. This type of vision is called Mosaic vision.

  • Nervous system is typical annelids type. Nervous system is made up of a dorsal brain and a double ventral nerve cord with a ganglion in each segment.

  • Animals are mostly unisexual and show sexual dimorphism.

  • Fertilization is internal and animals are oviparous or ovoviviparous. Development is usually indirect. Some animals show parthenogenesis .

Common examples of arthropods are Cancer (Crab), Palaemon (prawn), Scolopendra (centipede), Lycosa (spider), Cockroach, Julus (millipede), etc.

Characteristics of phylum echinodermata

Jacob Klein (1738) has been introduced the term echinodermata for the first time. The echinoderms are exclusive marine, centerocoelous, coelomate, triplobalstic animals having pentamerous radial symmetry derived from original bilateral symmetry without definite head with a peculiar water vascularsystem of coelomic origin. About 6,000 species of echinodersm are known to us which includes starfishes, brittle stars, sea urchins, sea cucumbers, sand dollars and sea lilies. General characteristics of ehinoderms are:

  • Animals are unsegmented, circular or spherical or star shaped, without head or brain.

  • In juvenile stage, body is bilaterally symmetrical but in adults body has pentamerous radial symmetry.

  • Echinoderms have calcareous endoskeleton consisting of separate paltes or pieces bearing external spines or protuberances.

  • No special respiratory system is present. Tube feet function as gills during respiration.

  • Vascular system is supported by tube feet. Tube feet help in locomotion and respiration.

  • Alimentary canal is straight or coiled and simple.

  • Definite excretory organs are absent.

  • Nervous system is of primitive type. It is without brain and consists circumoral ring radial nerves.

Characteristics of phylum hemichordate

Hemichordata is the group of animals which show characters of both chordates and non chordates. Sometimes this group is referred as invertebrate chordates. Due to the presence of pharyngeal gill slits, hollow dorsal nerve cord and the so called notochord, the animals of this group were earlier placed in the phylum chordate. But later on, it was realized that their notochord is not like that of the notochord of actual chordates. Therefore this group was separated from chordate and a new phylum hemichordeata was formed. The important characteristics of hemichordates are:

  • Oorganisms are exclusively marine. These are solitary, colonial or sometimes living in a tube.

  • Animals are triploblastic with bilateral symmetry.

  • Body is long, worm like, soft, compact and stalked.

  • Body is easily divisible into proboscis, collar and trunk.

  • The epidermis of body wall is single layered containing nucus secreting glandular cells.

  • Coelom is enterocoelous.

  • Alimentary canal is complete, straight or U-shaped.

  • Respiration takes place by means of dorsally placed pharynx. Number of gill slits is variable.

  • A median dorsal and a median longitudinal blood vessel constitute the circulatory system. The two vessels are connected with lateral vessels.

  • Excretory system consists of a proboscis gland or glomerulus.

  • Nervous system is of primitive type. It is in the form of epidermal nerve plexus.

  • Fertilization is external.

Common examples of hemichordata are Balanoglossus, Saccoglossus, Rhadopleura and Cephalodiscus.

Last words

In my two articles, you have read about different phyla of animallia. All these phyla belong to non chordata. The phylum chordata is divided into five classes.

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