Maharashtra Board Class 11 Biology Chapter 4 Kingdom Animalia PDF Download

Kingdom Animalia

You are familiar with animals, their general characteristics and great diversity observed in this group. Let us learn about how this diverse group is classified systematically.

Can you recall?

1. What is the basis for classification?

2. Who proposed Five Kingdom classification system?

3. What is the need and importance of classification?

4.1 Criteria Used For Animal Classification

Grades of organization - Cellular, Cell-Tissue, Tissue-Organ, Body Symmetry-Asymmetry, Radial Symmetry, Bilateral Symmetry, Body Cavity - Acoelomate, Pseudocoelomate, Coelomate. Germ Layers -Diploblastic, Triploblastic. Segmentation-Unsegmented, Segmented.

4.2 Animal Body Plan

a. Cell Aggregate Plan: In this body plan, cells do not form tissues or organs. Their is minimal differentiation and division of labour among cells. It is found in porifera.

b. Blind Sac Body Plan: In this body plan, body is like a sac with single opening. Digestion is carried out in this sac-like structure where ingestion and egestion takes place through same opening. e.g. Members of Phylum Cnidaria.

c. Tube Within Tube Body Plan: Digestive system is present in tube-like body cavity. Mouth and anus are present at two separate ends of digestive system. Annelida onwards all phyla show this type of body plan.

Observe and Discuss

Observe the diagram given below and discuss the criterias of classification.

4.3 Animal Classification

1. Phylum: Porifera

(pori-pores; feron-bearing)

e.g. Scypha, Euspongia (Bath sponge), Euplectella (Venus' flower basket)

These are aquatic animals, most of them are marine and few are fresh water. They are also called 'sponges'.

Most of them have asymmetrical body. Body of these animals consists of many cells with little division of labour. Hence their body is considered as a colony of different types of cells.

These are sedentary animals. On their body, they bear numerous minute pores called 'ostia' through which water enters in the body cavity- spongocoel. Water leaves the body through single large opening called 'osculum'.

Water is circulated in the body through the 'canal system'. During its circulation, cells of the animal body absorb food, exchange respiratory gases and release excretory products.

Spongocoel is lined by special flagellated cells called 'choanocytes' or 'collar cells'. Beating of flagella creates water current.

Body of these animals is supported by calcareous or siliceous 'spicules' or proteinaceous 'spongin fibers'.

They reproduce asexually as well as sexually. Asexual reproduction is performed by fragmentation and gemmule formation. These animals have ability of regeneration. Sexual reproduction is performed by formation of gametes. Fertilization is internal. Development takes place through indirect larval stage.

Teacher's Note

Sponges are simple animals that live in water and look like rocks. Just like your body has cells, sponges have many cells working together.

Exam Trick

Remember: Sponges have pores called ostia - think of them as tiny doors where water enters. The big hole where water leaves is osculum - like the main exit door.

Points to Remember

Sponges are aquatic animals found mostly in ocean water.
They have tiny pores called ostia for water to enter.
A large opening called osculum lets water exit.
They reproduce both asexually and sexually.
They can grow back lost parts through regeneration.

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Which are the larval stages of Porifera?

2. Phylum: Cnidaria

e.g. Hydra, Aurelia (Jelly fish), Physalia (Portuguese man-of-war), Adamsia (sea anemone), Diploria (Brain coral), Gorgonia (sea fan).

They are aquatic, mostly marine and few are fresh water forms. They are sessile or free swimming. They show radial symmetry and are diploblastic with blind-sac body plan. Animals exhibit two body forms. Polyp is cylindrical form (Hydra) and medusa is umbrella-like (Aurelia - Jelly fish).

Body cavity is meant for circulation as well as digestion. Hence called gastrovascular cavity or coelenteron. Tentacles bear cnidoblasts or stinging cells which are meant for anchorage, offence and defence. Cnidarians reproduce both asexually and sexually. Asexually reproduction takes place by budding and regeneration. Sexual reproduction takes place by gamete formation. They exhibit alternation of polypoid generation with medusoid generation. This phenomenon is called metagenesis i.e. polyps produce medusae asexually and medusae produce polyps sexually. (e.g. Obelia)

Teacher's Note

Jellyfish and sea anemones are cnidarians with stinging tentacles. When a small fish touches the tentacles, they sting and catch the fish for food, like how a net catches fish.

Exam Trick

Remember: Cnidaria means "stinging cells" - think of cnidarians as animals with thousands of tiny stinging cells on their tentacles to catch food and protect themselves.

Points to Remember

Cnidarians have stinging cells called cnidoblasts on their tentacles.
They show radial symmetry - like a circle in all directions.
They have two body forms: polyp and medusa.
Jellyfish is medusa form and hydra is polyp form.
They reproduce both asexually by budding and sexually by gametes.

3. Phylum: Ctenophora

These are commonly called comb jellies or sea walnuts. These are exclusively marine, free swimming animals. Body is diploblastic, radially symmetrical with blind-sac body plan. Animals have tissue-level organisation. Locomotion is carried out by eight rows of cilliated comb plates. Characteristic feature of ctenophores is bioluminescence. Like cnidarians, ctenophores also exhibit extra and intracellular digestion. Reproduction is sexual with indirect development. Cnidoblasts are absent hence these are called acnidarians. Instead, they have colloblasts (sticky cells) to capture the prey. Ctenophora is represented by very few members, hence it is considered as one of the minor phyla. e.g. Pleurobrachia, Ctenoplana.

Teacher's Note

Comb jellies are like jellyfish but they have special comb-like rows to move instead of tentacles. They live only in the sea and glow in the dark like fireflies.

Exam Trick

Remember: Ctenophora = comb jellies with eight rows of combs that help them swim. They glow in dark - think of them as glowing combs moving in the ocean.

Points to Remember

Comb jellies are found only in salt water (marine).
They move using eight rows of comb-like plates.
They can produce light in the dark (bioluminescence).
They have sticky cells called colloblasts to catch food.
They do not have stinging cells like cnidarians.

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