Ch 4Animal Kingdom — Class 11 Biology, concept-first.

Look around at the animals you come across in everyday life — a stray dog, a sparrow, an earthworm turned up by a spade, a butterfly in the garden — and it is obvious how different they are from one a…

Despite all the differences in shape, structure and outward form among animals, a number of deep, fundamental features recur across many groups — and it is these shared features, not superficial appea…

Every member of the kingdom Animalia is multicellular, but multicellularity by itself does not mean that all animals build their bodies in the same way.

Animals can also be sorted according to their body symmetry — that is, whether the body can be divided into matching halves, and in how many planes such a division is possible.

Another fundamental character used in classification is the number of germ layers — the embryonic cell layers from which the whole body develops.

The coelom, or body cavity, is another feature of great importance in classification, and it depends on the third germ layer. The coelom is a cavity that lies between the body wall and the gut wall.

In some animals the body is built up out of a series of repeated units, or segments. When the body is divided, both on the outside and on the inside, into such segments, with at least some of the orga…

The notochord is a rod-like structure that forms on the dorsal (back) side of the body during embryonic development in certain animals. It is derived from the mesoderm.

The fundamental characters examined so far — the level of organisation of the cells, the body symmetry, the number of germ layers, the nature of the coelom, the presence of segmentation, and the prese…

The members of the phylum Porifera are the animals commonly known as sponges. They are among the most primitive of the multicellular animals, and they stand at the cellular level of organisation, in w…

Coelenterates, also called cnidarians, are aquatic animals that live mostly in the sea. Some stay fixed to a surface (sessile) while others swim freely, and all of them share a radially symmetrical bo…

Ctenophores are marine animals commonly called sea walnuts or comb jellies. They live only in the sea and have a radially symmetrical body in which the parts are arranged around a central axis.

The members of this phylum have a body that is flattened from the upper to the lower surface (dorso-ventrally flattened), which is why they are commonly called flatworms.

Members of this phylum have a body that appears circular when cut across (circular in cross-section), which gives them the common name roundworms.

Annelids live in many settings: some are aquatic, in the sea or in fresh water, while others are terrestrial. Most are free-living, though a few are parasitic.

This is the largest phylum in the animal kingdom, and it includes the insects. In fact, more than two-thirds of all the named species on earth are arthropods, which makes this by far the most successf…

Molluscs form the second largest phylum in the animal kingdom. They are found on land as well as in water, whether marine or fresh water, and they show an organ-system level of organisation.

The animals of this phylum carry an internal skeleton (endoskeleton) built from calcium-containing plates called ossicles, and their spiny bodies give the phylum its name, which means spiny bodied.

This phylum was once treated as a sub-phylum within the phylum Chordata, but it is now recognised as a separate phylum placed among the non-chordates.

Phylum Chordata gathers together all animals that share a small set of defining structural features at some point in their life.

Class Cyclostomata contains the most primitive of the living vertebrates — the jawless fishes. All of its present-day members live as ectoparasites on certain fishes, attaching to the host from the ou…

Class Chondrichthyes comprises the cartilaginous fishes — fishes whose entire internal skeleton is made of cartilage rather than bone.

Class Osteichthyes contains the bony fishes — fishes whose skeleton is made of true bone. Like Chondrichthyes, they belong to the super class Pisces, but they differ from the cartilaginous fishes in s…

Class Amphibia includes animals whose very name reflects their double life. The word comes from the Greek amphi, meaning dual, and bios, meaning life, because amphibians can live in both aquatic and t…

Class Reptilia takes its name from the way its members move: the Latin words repere and reptum mean to creep or to crawl, describing the reptilian mode of locomotion.

Class Aves contains the birds. Their body plan is thoroughly adapted for flight, and this shapes almost every characteristic of the class. Aves belongs to the super class Tetrapoda.

Class Mammalia is the most advanced class of vertebrates and occupies an extraordinary range of habitats — polar ice caps, deserts, mountains, forests, grasslands and dark caves.

The animal kingdom, for all its diversity, can be sorted into an orderly scheme because animals share a limited set of fundamental structural features.

Higher-order thinking problems from the NCERT Exemplar.