Ch 2Kingdom Animalia — Class 11 Zoology, concept-first.

Kingdom Animalia is vast: its members are eukaryotic, multicellular and heterotrophic, and together they span roughly 35 phyla, of which about 11 are considered major phyla.

Multicellular animals are structurally and functionally very different from one another, yet they still share certain fundamental features that make it possible to organise that diversity into a coher…

Every member of Kingdom Animalia is a metazoan — a multicellular animal whose cells cannot exist independently and must divide labour among themselves.

During early embryonic development, an animal's tissues and organs are built from either two or three primary cell layers, called germ layers, and this single developmental fact predicts a great deal…

Symmetry describes how an animal's body parts are arranged relative to a central axis, and it is closely tied to how an animal lives: sedentary or drifting animals tend toward radial symmetry, while a…

The coelom is the body cavity that lies between the body wall and the alimentary canal, and whether an animal has one — and how it is lined — is one of the clearest lines separating the animal phyla.

Two further structural features complete the basis-of-classification toolkit.

Every criterion covered in section 2.1 — organisation level, germ layers, symmetry, coelom, and segmentation/notochord — combines into one nested classification scheme rather than acting as five separ…

Invertebrates — animals that lack a vertebral column — make up roughly 99 percent of all described animal species, spanning everything from the cellular-level sponges to the chordate-adjacent hemichor…

Porifera (Latin poros, pore; ferre, to bear) are the sponges, the most primitive multicellular animals in the animal kingdom.

Cnidaria (Greek knide, needle or sting) — formerly called Coelenterata — are aquatic animals that may be sessile or free-swimming, solitary or colonial, and are radially symmetrical except for sea ane…

Ctenophora (Greek ktenos, comb; phoros, bearing) are exclusively marine, diploblastic animals with tissue-level organisation and radial symmetry (more precisely, biradial symmetry — see section 2.1.3)…

Platyhelminthes (Greek platy, broad or flat; helmin, worm) are the flatworms — bilaterally symmetrical, triploblastic, acoelomate animals that are nonetheless the first phylum in the classification sc…

Aschelminthes (Greek askes, cavity; helminths, worms) — previously classified as Nematoda — are the round worms, named for their circular cross-section.

Annelida (Latin annulus, a ring) were the first animals to evolve true segmentation, and the phylum's name reflects the ringed appearance this gives their body.

Arthropoda (Greek arthros, jointed; podes, feet) is the largest phylum in the entire animal kingdom, and contains its single largest class, Insecta, whose total species estimates range from 2 to 10 mi…

Mollusca (Latin molluscus, soft-bodied) is the second-largest animal phylum, found in terrestrial and aquatic (marine or freshwater) habitats and showing organ-system organisation.

Echinodermata (Greek echinos, spiny; dermos, skin) are exclusively marine animals, and the name refers to their mesodermal endoskeleton of calcareous ossicles, which often bears spines.

Hemichordata (Greek hemi, half; chorde, string) were originally treated as a subphylum of Chordata (Prochordata), but are now recognised as an independent phylum of invertebrates positioned close to E…

Chordata is the largest and most familiar phylum in the animal kingdom, uniting fishes, amphibians, reptiles, birds and mammals with less familiar groups such as the lancelets (Amphioxus) and the tuni…

Urochordata or Tunicata (Greek oura, a tail; Latin chorda, cord) are exclusively marine animals, commonly known as sea squirts.

Cephalochordata (Latin cephalo, head; Greek chorda, cord) are small, fish-like, coelomate marine animals found in shallow waters, where they lead a burrowing way of life.

Vertebrates, also called the "higher chordates," are set apart from the other two subphyla by one key developmental fact: they possess a notochord only during the embryonic stage.

Cyclostomata (Greek cyklos, circle; stomata, mouth) are the most primitive living vertebrates, and every member of the class is placed in division Agnatha because none of them possess jaws.

Chondrichthyes (Greek chondros, cartilage; ichthys, fish) are marine fishes whose entire endoskeleton is built from cartilage rather than bone, with the notochord persisting throughout life.

Osteichthyes (Greek osteon, bone; ichthys, fish) includes both marine and freshwater fishes with a bony endoskeleton and a typically spindle-shaped (fusiform) body — the largest and most diverse class…

Amphibia (Greek amphi, both; bios, life) were the first vertebrates, and the first tetrapods, to live in both aquatic and terrestrial habitats — the class's name reflects this dual life.

Reptilia (Latin repere/reptum, to creep or crawl) are mostly terrestrial animals, and their body is covered by dry, cornified skin bearing epidermal scales or scutes — the key adaptation that let them…

Aves (Latin avis, bird) are commonly known as birds, and the class's single characteristic feature — found in no other living animal — is the presence of feathers, together with the ability to fly (lo…

Mammalia (Latin mamma, breast) is found in essentially every habitat, and is defined by two features unique among animals: the body is covered by hair, and every member possesses mammary glands, which…

This Evaluation set closes the chapter by testing the same criteria built up across sections 2.1–2.4: the five bases of classification (organisation level, germ layers, symmetry, coelom, segmentation/…

Sample papers and previous-year board questions for this subject.