Kingdom Animalia

Kingdom Animalia

Characteristics of kingdom Animalia

The characteristics of kingdom Animalia are as follows:

• They posses metazoans i.e. multicellular organisms.
• These harbours diverse forms of animals from sponges to mammals.
• Their type of body organization is either cellular or tissue or organ or organ system.
• Almost all animals are motile or shows locomotion expect sponges.
• They are provided with muscles and nerve cells except sponges.
• They have the heterotrophic mode of nutrition, most of them have holozoic nutrition but some shows the parasite on other animals.
• They are the basic consumers on the soil and form links in various food chains and food webs.
• Generally, lower animals reproduce by both asexual and sexual methods and higher animals reproduce by the sexual method.
• Embryonic stage is present.
• They show great difference in the habitat. Some are aquatic (freshwater or marine), some are terrestrial (living on land), some are amphibians (living on land as well as in water).

Phylum: Porifera (Sponges)

Definition: Porifera is called as asymmetrical or radially symmetrical multicellular organisms with the cellular type of body organization without tissues and organs but with the body perforated by pores and with the characteristic skeleton of calcareous or siliceous spicules or of sponging fibres.

General characteristics

1. Habit and habitat: All sponges are aquatic, mostly marine, rarely freshwater (e.g., Spongilla). Solitary or colonial. All are sessile; attached on the substratum.
2. Body form: The body form varies considerably. They posses vase-like, cylindrical, cup-shaped, spherical or disc-like, or irregular. Their body is porous, i.e., provided with pores. The pores are of two types : inhalant pores are called Ostia (sing ostium) and excellent pores are called oscula (sing. osculum). Interior space of sponge body is called spongocoel which is lined by choanocytes.
3. Symmetry: Most of the sponges are asymmetrical. Some are mainly radially symmetrical.
4. Germ layers: From the evolution point of view, the sponges are the first multicellular diploblastic animals, I,e., derived only from two embryonic germ layers, viz, ectoderm and endoderm which are separated by an intermediate noncellular layer known as mesenchyme.
5. The level of body organization: The sponges have the cellular grade of body organization.
6. Canal system: Three types of canal systems are found in sponges- Ascon, Sycon and Leucon type. The canal system helps the sponge in nutrition, respiration, excretion, and reproduction.
7. Skeleton: Almost all sponges possess an internal skeleton. It may consist of calcareous or siliceous spicules or of fine sponging fibers.
8. Digestion: It is intracellular and takes place inside food vacuoles as in the type protozoans.
9. Respiration: Exchange of gasses occurs by diffusion through the plasma membrane of the cells as in protozoans.
10. Excretion: Removal of metabolic wastes also occur by diffusion through the plasma membrane of the cells as in protozoans.
11. Reproduction: Both asexual and sexual reproduction occur in sponges. Asexual reproduction occurs by budding and gemmules. Sexual reproduction occurs by fusion of gametes.
12. Development: Zygote undergoes holoblastic cleavage ( the complete division of zygote). The development is indirect and includes a free-swimming ciliated larva called Amphiblastula (e.g Sycon) or Pareenchymula (e.g. Leucosolenia) for dispersal of the species.

Phylum: Coelenterata (cnidaria)

Definition: Phylum Coelenterata is defined as diploblastic metazoan with tissue grade of body organization having nematocysts and a single gastrovascular cavity or the coelenteron.

General characteristics

1. Habit and habitat: All are aquatic, mostly marine, few freshwater like the hydra. They are solitary or colonial. Both sessile and free swimming forms are found.
2. Body form: They show polymorphism i.e. occurrence of more than one type of individuals in their colonies having different forms performing different functions. E.g., polyps, blastostyles, and medusa. Polyps provide food to the colony. Blastostyles produce medusa by budding. Medusae are sexual zooids which take part in sexual reproduction by producing gametes.
3. Symmetry: They show radial or biradial symmetry;
4. Germ layers: They are diploblastic animals i.e derived only from two embryonic germ layers, viz, ectoderm and endoderm which are separated by an intermediate noncellular gelatinous layer called the mesoglea.
5. The level of body organization: They have tissue level of body organization.
6. Tentacles: Mouth of polyps and margin of medusae are encircled by numerous tentacles which help in food capture, ingestion, the defense as well as locomotion. The tentacles are provided with nematocysts.
7. Digestive tract: The hollow body cavity known as coelenteron or gastrovascular cavity, contains only one opening which acts as mouth as well as anus. Thus there is present incomplete digestion tract.
8. Digestion: Both intra and extra-cellular digestion are present.
9. Respiration and excretion: These are carried out through the body surface by diffusion.
10. Reproduction: Both asexual and sexual reproduction are found. Asexual reproduction takes place by building and regeneration whereas sexual reproduction occurs by fusion of gametes.
11. Development: The cleavage is holoblastic. Development is either direct or indirect. During indirect development, a free-swimming ciliated larva called the planula larva is found.
12. Alternation of generations: The life-history commonly illustrates the phenomenon of alternation of generations or mutagenesis in which an asexual, sessile, usually colonial, polypoid generation alternates with a sexual, free swimming , usually solitary, medusoid generation.

References

Arvind, Keshari K. and Kamal K Adhikari. A Textbook of Biology. Vidyarthi Pustak Bhander.

Michael J.Pleczar JR, Chan E.C.S. and Noel R. Krieg. Microbiology. Tata Mc GrawHill, 1993.

Powar. and Daginawala. General Microbiology.

Rangaswami and Bagyaraj D.J. Agricultural Microbiology.