As we have already discussed the basis of classification of the animal kingdomaccording to the class 11 text, so now we will be learning the different phylum of the animal kingdom as prescribed in the class 11 syllabus. The article has been prepared in the form of notes for quick and rapid understanding of the chapter by the students.
Porifera (Common Name-Sponge) – First Phylum Of Animal Kingdom
The first phylum of the animal kingdom that has been discussed in the class 11 text is the Phylum Porifera or commonly known as the sponge.
Robert Grant named the animals in this group as Porifera. The science that deals with the Study of sponges are known as Parazoology. Phylogenetically sponges are evolved from choanoflagellates (Proterospongia). Sponges are multicellular primitive forms. All sponges are aquatic, mainly marine however few of them are in freshwater also. The body is sessile, solitary or colonial. The entire body has pores on its surface i.e. numerous small mouth lets called as Ostia and one main opening for exit called Osculum.
General Characters of Poriferans
Sponges show diversity in the body forms and shapes that have irregular shape usually asymmetrical. (Radial symmetry in Leucosolenia). Sponges show a cellular level of organization in the body with two germ layers i.e. Diploblastic. They lack head and appendages in their structure.
Body wall in adults have
ο Outer ectoderm or dermal layer or pinacoderm in pinacocytes (Flat cells), porocytes (oval cells)
ο Inner endoderm (Choanocytic layer) or choanoderm collar cell or choanocytes (Flagellated)
ο Between the two germinal layers, gelatinous non-cellular material mesenchyme is present in the sponge. It has fine dispersed spongy fibres and many spicules.
ο The body wall encloses a large central cavity of a sponge that is called the spongocoel or paragastric cavity.
ο Choanocytes contain flagella that form the outer lining in Spongocoel and also in some canals.
ο Choanocytes beating of flagella causes water currents which are very important for the sponge to survive. Water that enters in the sponge through Ostia perforating porocytes and several canals and then enters in spongocoel and finally exit out through the large aperture osculum.
ο Canal system or water transport system: Canal system in poriferans help in grasping food (nutrition), respiration and excretion processes.
Asexual means – By budding and fragmentation. Budding can be of two types:
a. Exogenous budding – occurs during favourable conditions.
b. Endogenous budding – gemmules formation takes place during adverse conditions.
They contain Archaeocyte cells and covered by a thick protective coat.
(ii) Sexual means – Sponges are Hermaphrodite or monoecious, fertilisation is internal and cross (Protogynous condition). Development is indirect with larvae formation. Names of larva and the organism in which it is formed:
Unique Features of Porifera
Pores all over the body. Cellular body organization. A canal system for water currents that are intercommunicating cavities through which the water current pass. Lack of mouth and digestive cavity. Choanocytes that cover the main cavity (spongocoel) or certain canals (radial canals). Presence of spongin fibres.
Coelenterata – Second Phylum Of Animal Kingdom
The second phylum of the animal kingdom that has been discussed in the class 11 text is the Phylum Coelenterata or also known as the Cnidaria.
Coelenterata was given its name by Leuckart. Hatschek gave another name Cnidaria which was based on the capability of stinging cells. Around 9000 species, many of the organisms are marine, however few of them are freshwater (Hydra) carnivorous members. Some are fixed to the substratum or can be free floating also. Body forms are basic (Dimorphic)
Either or both zooids may occur in a species. If both zooids are found in a species, the two forms are in alternate ways in the life cycle. Polyps form medusa asexually and medusa develops the polyps sexually (Alternation of generation or Metagenesis) e.g. – Obelia. Group of different types of zooids in polyp or medusa shows polymorphism in pattern. Coelenterates usually have radial symmetry. Coelenterates consists of two germs layers ectoderm and endoderm i.e. They are diploblastic (mesogloea between two layers).
Interstitial cells are totipotent cells of coelenterates that are present in both the layers of the body wall. Coelenterates have a higher level of organization from cell i.e. tissue. Cnidoblast or Cnidocyte (have the stinging capsule called as Nematocyst) present on the tentacles and body of the organism are used for anchorage on the substratum, defence and for the prey capture. Horny or calcareous exoskeleton can be present to support the body of coelenterates. E.g. – Corals.
There is just a central cavity called coelenteron that has a single aperture, mouth and thus the body has incomplete digestion tract (Blind sac). Digestion is both extracellular and intracellular i.e. digestion takes place in coelenteron as well as in food vacuole of gastrodermal cells. Coelenterons distribute the food that is partly digested by it. This dual role in the coelenterons was named as the gastrovascular cavity.
Respiration and excretion occur through diffusion of gases from the body surface. The excretory matter is ammonia. The nervous system is of the diffused type and consist of non-polar neurons. These are the first phylum that has nerve cells that conduct impulses in all directions.
Coelenterates have epidermis which consists of epithelia-muscular cells of which the muscular part drives inward while the epithelial part drives out of the body. They also have glandulo muscular cells which secrete a sticky substance that attaches the body to the substratum.
Tissue level of organization is found in the body. Special stinging properties in the cells of the cnidoblasts that helps for defence and food adherence. Incomplete digestive tract with one mouth opening is present in the body wall. A simple nervous system with nerve cells in the network arrangement and fibres. Simple gonads that lack the gonoducts.
Ctenophora – Third Phylum Of Animal Kingdom
The third phylum of the animal kingdom that has been discussed in the class 11 text is the Phylum Ctenophora.
Eschescboltz named the phylum as Ctenophore. These animals have a beautiful structure and delicate body and are also famous for the same. The body has a comb plate that glows in sunlight and gives the effect of a rainbow. The Ctenophorans are known as “Sea gooseberries” or “Comb-jellies” or “Sea-walnuts”. They lack nematoblasts, hence are also called as “acnidarians”. All the animals of this phylum are marine and pelagic (floating on sea surface) and have Bioluminescence (Property of emitting light in the dark) in the cell.
General Characters of Ctenophora
The body can be spherical, cylindrical or pear-shaped in structure. The body has a soft, transparent, jelly-like appearance that has radial symmetry (biradial symmetry) with tissue level of body organization. Animals are diploblastic with two germ layers present. They lack a skeleton, circulatory, respiratory and excretory systems. The body surface has cilia that join together to form 8 ciliary combplates that helps in the locomotion of the organism. Digestion occurs through extracellular and intracellular methods.
Animals are carnivorous. Tentacles may be present in a pair, are long solid structures that have colloblasts (lasso cells) instead of nematoblasts on the tentacles which help in prey catching. All animals are bisexual and reproduce sexually. Fertilisation is an external process taking place in water. Development of the zygote is of the indirect type. Life cycle involves a free living immature ciliated cydippid larva stage, found in some organisms.
Hormiphora– sea walnut
Ctenoplana – Commensal with Alcyonium
Cestum – Swimming eye of Cat.
Euchlora rubra – Ctenophore with cnidoblast. (Exception)
Platyhelminthes-Fourth Phylum Of Animal Kingdom
The fourth phylum of the animal kingdom that has been discussed in the class 11 text is the Phylum Platyhelminthes.
Gagenbaur was a naturalist to name the Platyhelminthes. This phylum includes flatworms that are dorsoventrally flattened structures, most primitive bilateral symmetrical animals, can be free-living (terrestrial, freshwater or marine) or as a parasite on a host.
The Study of worms that cause a parasitic infestation in the human is called as helminthology. Most of the members in this phylum are the endoparasite having hosts as vertebrates. Some organisms are found growing in aquatic habitat as well.
General characteristics of Platyhelminthes
Body organization has organ grading of the tissues. Body is triploblastic i.e. body has originated from all the three germinal layers called ectoderm, endoderm and mesoderm. The body has bilateral symmetry. The body lacks locomotory organs instead have adhesive organs like suckers, hook, etc. in the parasitic forms that help in attachment and also to take in the food. The epidermis is syncytial that may have cilia on the surface. The body wall of parasitic animals contains a thick cuticle which is called as tegument which protects the parasite from the host’s digestive enzymes secreted by the body surfaces (Epidermis).
Digestive tract if present has a mouth and lacks anus or completely absent like in Tapeworm. Food enters through the mouth or through the body surface. These are acoelomate i.e. lack a body cavity. The body lacks skeleton and circulatory systems. The body form is maintained by the turgid fluid present in the parenchymal meshes (Hydroskeleton). The respiration occurs through the body surface. Anaerobic respiration is also found, in internal parasite like Taenia.
Excretion takes place with the organs protonephridia or flame-cells (Solenocytes). Also, they perform osmoregulation. The nervous system is made up of the nerve ring, nerve cord and peripheral nerves (ladder-like) Platyhelminthes are bisexual animals who have a complex and well-developed reproductive system. Fertilization is internal which is either self or cross. Development of the zygote may be direct or indirect.
Bilateral symmetry. Organ level of body organization. Head is present that has sense organs located at the front end. Body made from three germ layers. Muscle layers are found in the body wall and gut. Nervous system with brain ring and nerve cords. An organized excretory system with flame cells, and gonoducts and copulatory organs
Aschelminthes or Nemathelminthes – Fifth Phylum Of Animal Kingdom
The fifth phylum of the animal kingdom that has been discussed in the class 11 text is the Phylum Aschelminthes, also known as the Nemathelminthes.
Gegenbaur named the Phylum as Nemathelminthes. The phylum includes roundworms (Circular in cross-section). Nematodes are omnipresent, growing in fresh water, sea water, soil, humus-rich soil. Many of them are as a parasite in plants and animals.
General characters of Nemathelminthes
Animals have a cylindrical body, tapering at both the ends, are without any segmentation. The body has Bilateral symmetry with organ Level of organization and having a tube within a tube body plan. The body has been originated from triploblastic germ layers. Body wall includes cuticle, epidermis (Syncytial) and muscle layer (only Longitudinal). The body cavity is pseudocoel and lacks a mesoderm lining (developed from embryonic blastocoel) and it contains pseudo coelomic fluid. Skeleton is not mineralized, instead, a pseudocoelom with high fluid pressure maintains the body shape which is called hydroskeleton.
Digestive tract has both the openings of mouth and anus along with differentiated, muscular pharynx and intestine and thus is a complete system. Respiration occurs via the body surface through diffusion. The body lacks a circulatory system. The nervous system is made up of nerve ring (Brain) and longitudinal nerve cords. The excretory system has an H-shape excretory tube (intracellular canal) or Protonephridia – (Renette cell). Excretory matter produced by the body is ammonia.
Reproduction system is developed and sexes are in separate organisms (Dioecious). Sexual dimorphism is present (sexes differ in size and structure). Male is shorter than the female with a curved caudal end, while the female is straight. Male contains penial spicules for copulation. Genital tract and digestive tract are connected and form cloaca. Genital tract opens independently. (Cloaca absent).
Fertilisation occurs internally and development can be either direct or indirect. A number of cells in the body are fixed from larva to adult and this phenomenon is called as Eutely.
Syncytial epidermis lining all over. Body wall muscular of longitudinal fibres only. Pseudocoel, a body cavity that lacks mesodermal coelomic epithelium lining. Complete digestive tract with mouth and anus. Fluid-filled body cavity. Separate sexes.
These are the five phyla out of the eleven phyla of the animal kingdom of Class 11 that we have discussed in this articles. We will learn about the remaining phyla of the animal kingdom of Class 11 in our subsequent article.