Characteristics of different phyla of kingdom animalia part I
Are you looking for a good article about characteristics of different phyla of kingdom animalia? In this article you will find the characteristics of porifera, coelenterata, platyhelminthes and nematodes. To know the characteristics of different phyla of animalia, please read this article.
The two main kingdoms of five kingdom classification are plant kingdom (Plantae) and animal kingdom (animalia). The animal kingdom show enormous diversity. On the basis of presence and absence of notochord, the animal kingdom has been classified into two sub kingdom: 1. Non- chordata and 2. Chordata.
Non chordates do not possess notochord at any stage of their life, but chordates possess the notochord at least in some stage of their life. Non chordates include a number of phyla. The major phyla are:
- Phylum – Porifera
- Phylum – Coelenterata
- Phylum – Platyhelminthes
- Phylum – Nematoda
- Phylum – Annelida
- Phylum – Mollusca
- Phylum – Arthropoda
- Phylum – Echinodermata
- Phylum - Hemichordata
- Phylum - Chordata
Characteristics of phylum Porifera
Phylum porifera includes most primitive and simplest of all multi-cellular animals commonly known as sponges. Robert Grant game the name porifera to sponges. About 5,000 species of sponges are known to us. Most of the sponges are marine in habitat, but some of them live in freshwater. Adults are sessile and often found in colonies attached to under water objects. Some spnges have been reported from rocks more than 600 million years old. The main characteristics of sponges are as follows:
- Sponges are multi-cellular organisms with cellular grade of body organization. Sponges do not have any tissues or organs. Body of sponges is diploblastic, i.e., body consist of two germ layers.
- Sponges are sedentary aquatic animals mostly marine, a few freshwater forms occurring singly or colonies.
- The shape of sponges is variable mostly plant like, radially symmetrical or asymmetrical.
- Body surface is perforated by numerous minute inhalant pores, the ostia, to admit a water current which after circulating through a canal system inside the body pases out through more larger exhalent openings, the osculum.
- Animals lack alimentary canal. The body cavity is spongocoel, which opens exteriorly through osculum act as digestive canal. Digestion is entirely intracellular.
- The skeleton is internal contained in the mesenchyme and made up of separate crystalline calcareous orsiliceous spicules or of irregular sponging fibers or of both.
- Sponges reproduce either asexually by budding or sexually by the formation of gametes. Most sponges are hermaphrodite. Fertilization is internal and development is indirect with larval stage.
Common examples of porifera are leucosolenia, Sycon, Spongilla, Euspongia, etc.
Characteristics of phylum Coelenterata
Leuckart has used the term coelenterate for the first time. The phylum coelenterate includes about 9,000 species, mostly marine. Coelenterates are multi cellular organisms that are more highly organized than sponges and show polymorphism. The main characteristics of coelenterates are given below:
- Coelenterates are multi cellular animals showing cell tissue level of body organization with most of the cells specialized for different functions and some forming a tissue. Division of labour is found in coelenterates.
- Cnidarians are diploblatic metazoans; the body wall is made up of two layers, the outer ectoderm and inner endoderm with middle non living gelatinous layer mesoglea.
- Head and segmentation are absent.
- Tentacles are found in coelenterates, which encircle the mouth in one or more whorls and are used for food capture, intake and defense.
- Coelome is not found in them. Only one cavity found in the body called coelenterons, which is enclosed by endoderm.
- Nematocysts are found in the tentacles, which are organs for defense and also used to catch the food.
- A network of sensory cells called neuron is found all over the body in the body wall.
- Coelenterates exhibit two types of basic forms the polyp and the medusa. The polyp is a fixed or sessile zooid while the medusa is free swimming. The body of a polyp is cylindrical with mouth tentacles facing upwards and that of medusa in saucer shaped with mouth and tentacles facing downwards. In many coelenterates polyps give rise to medusa by vegetative budding and the medusa forms the polyp after sexual reproduction. This is known as alternation of generations or metagenesis.
- Respiratory and excretory systems are absent.
- Digestion is both intra cellular nad extra cellular.
- nervous system is of primitive type and made up of a nerve net.
- The body has a gastrovascular cavity which opens outside by an aperture. It serves both as mouth and anus.
- Reproduction is both asexual by budding leading to extensive colony formation and sexual by ova and sperms.
The common examples of coelenterates are Hydra, Obelia, Aurelia, Physalia, Corallium.
Characteristics of phylum platyhelminthes
Platyhelminthes are bilaterally symmetrical, dorsoventrally flattened acoelomate wormlike animals. Platyhelminthes are commonly known as flatworms. Most of them are parasitic and a few are free living animals. There are about 13,000 species of flatworms known to us living in different habitat. The main characteristics of platyhelminthes are:
- Animals of this phylum either free living or parasitic.
- Tissue organ level of body organization is found.
- Coelom is absent. i.e. animals are acoelomate.
- Flateworms are triplobalstic, bilaterally symmetrical, dorsoventrally flattened organisms with anteriorly differentiated into a definite head.
- Platyhelminthes have flattened body because of their primitive system of circulation nd excretion. Each cell of the body must be near to the body surface to get nutrients and oxygen and for the removal of waste products and carbon dioxide.
- Platyhelminthes have unsegmented body except in tapeworms. In Cestodes body is strobilated, i. e., body consists of large number of proglottids.
- Flatworm are with blind sac body plan.
- The alimentary canal is either absent or highly branched and only mouth is present and anus is absent.
- Platyhelminthes do not have any body cavity or coelom, various organs are embedded in a sort of solid packing tissue known as mesenchyme or parenchyma.
- Excretory system consists of flame cells.
- Nervous system is primitive and ladder like. The main system consists of a pair of cerebral ganglia or brain and two longitudinal nerve cords with transverse connections located at regular intervals.
- Adhesive structures like hooks, spines and suckers are present in parasitic forms.
- Most of the flatworms can reproduce asexually and by sexual means. Asexual reproduction occurs in many freshwater and land planarians by fission. Planarians have remarkable capacity of regeneration. In parasitic forms, development is indirect involving many hosts and larval stages.
Common examples of flatworms are Fasciola hepatica, Taenia solium, Planaria, Polystoma.
Characteristics of phylum nematoda
Nematodes are commonly known as roundworms. The term nemathelminthes was proposed by Geogenbaur. About 15,000 species of nematodes are known to us. They are free living or parasite. Some are marine, others live in freshwater, soil or in the body of other plants and animals as parasite. General characteristics of nematodes are:
- Animals of nemathilminthes phylum have tube within tube body plan. It has distinct mouth, pharynx, intestine and anus.
- Body is covered with cuticle.
- Posterior end of female is pointed while curved in male.
- The body is unsegmented, bilaterally symmetrical and cylindrical.
- Male is always shorter than female.
- Body is not differentiated into head, thorax and abdomen.
- Animals are pseudocoelomic.
- respiratory and circulatory systems are totally absent.
- Alimentary canal is straight with muscular pharynx and muscleless intestine.
- Excretory system is very simple. Excretory system is made up of excretory tube or glandular organs or both.
- Nervous system is made up of circular nerve ring which encircle esophagus. Several longitudinal nerve trunks arise anteriorly and posteriorly from the nerve ring.
- Animals are always dioecious that male and female individuals of a species are separate. Male genital duct opens into cloaca while female genital duct opens to exterior portion.
Common examples of nematodes are Ascaris lumbricoides, Ancyclostoma, Wuchereria, Enterobius, Loaboa, etc.
You have read the characteristics of phylum porifera, coeleterata, platyhelminthes and nematoda in this article. The characteristics of remaining phyla will be described in my next article .