Cyclostomes are marine but migrate to fresh waters for spawning (anadromous migration). After spawning within a few days they die. The larvae (ammocoete) after metamorphosis returns to the ocean.

In some animals, cells that perform similar functions are aggregated to form tissues. The cells of a tissue integrate in a highly coordinated fashion to perform a common function, due to the presence of nerve cells and sensory cells. This tissue level of organisation is exhibited in diploblastic animals like cnidarians. The formation of tissues is the first step towards evolution of body plan in animals (Hydra - Coelenterata).

The left ovary is well developed while the right ovary is atrophied.

1. Cyclostomes are marine but migrate to fresh waters for spawning. This is called anadromous migration.
2. After spawning they die within a few days. The larva after metamorphosis returns to the ocean.

The Ctenophores have eight external rows of ciliated comb plates (comb jellies) in the mesoglea which help in locomotion. Hence they are commonly called as comb jellies or sea walnuts

(i) Ctenidia: MandIe cavity has a number of feather like gills (ctenidia) are present, which are respiratory in function.
(ii) Ospharidiam: The anterior head regim of molluscs has ospharidium to test the purity of water and present in bivalves and gasropods.

1. Absence of nervous and muscular tissue indicates that sponges must have been one of the earliest forms in the course of evolution.
2. Absence of tissues indicate that the body organisation would have been at cellular level only without cells forming compact tissues.
3. Further this also indicates that sponges do not show locomotion since they have no means of gauging the surrounding because they lack muscular tissue.
4. They are sedentary since they lack muscular tissue

The Ctenophores have eight external rows of ciliated comb plates (comb jellies) in the mesoglea which help in locomotion. Hence they are commonly called as comb jellies or sea walnuts.

Chordata is the largest phylum with most familiar group of animals, such as fishes, amphibians, reptiles, birds and mammals and less known forms such as lancelets (Amphioxus) and tunicates (Ascidian). All chordates possess three fundamental distinct features at some stage of their life cyele.
1. Presence of elongated rod like notochord below the nerve cord and above the alimentary canal. It serves as a primitive internal skeleton.
2. It may persist throughout life in lancelets and lampreys. In adult vertebrates, it may be partially or completely replaced by backbone or vertebral column.
3. A dorsal hollow or tubular fluid filled nerve cord lies above the notochord and below the dorsal body wall. It serves to integrate and co-ordinate the body functions

(i) Their body is covered by hair, a unique feature of mammals. Some of them are adapted to fly or live in water.
(ii) Presence of mammary glands-is the most unique feature of mammals.
(iii) They have two pairs of limbs adapted for walking, running, climbing, burrowing, swimming and flying.
(iv) Their skin is glandular in nature, consisting of sweat glands, scent glands and sebaceous glands.
(v) Exoskeleton includes horny epidermal horns, spines, scales, claws, nails, hooves and bony dermal plates.
(vi) Teeth are thecodont, heterodont and diphyodont.
(vii) External ears or pinnae are present.
(viii) The heart is four chambered and possess a left systematic arch. Mature RBCs are circular, biconcave and non nucleated.
(ix) Mammals have a large brain when compared to other animals.
(x) They show greatest intelligence among all animals. Their kidneys are metanephric and are ureotelic.
(xi) All are homeothermic, sexes are separate and fertilization is internal.
(xii) eg. Platypus, Kangaroo, Monkey, Elephant.

(i) They are mostly terrestrial animals and their body is covered by dry, and cornified skin with epidermal scales or scutes.
(ii) Reptiles have three chambered heart but four chambered in crocodiles.
(iii) All are cold blooded amniotes.
(iv) Most reptiles lay cleidoic eggs with extraembryonic membranes like amnion, allantois, chorion and yolk sac.
(v) Excretion by metanephric kidneys and are uricotelic.
(vi) They are monoecious. Internal fertilization takes place and all are oviparous.
(vii) eg. Calotes (Garden Lizard), Draco (Flying Lizard), Crocodilus (Crocodile).

(i) This is the second largest animal phylum.
(ii) Molluscs are terrestrial or aquatic (marine or fresh water) and exhibit organ system level of body organisation.
(iii) They are bilaterally symmetrical (except univalves), triploblastic and coelomate animals.
(iv) Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and a visceral hump or visceral mass.
(v) A soft layer of skin forms a mantle over the visceral hump. The space between the visceral mass and mantle (pallium) is called the mantle cavity.
(vi) A number of feather like gills (ctenidia) are present, which are respiratory in function.
(vii) The digestive system is complete and mouth contains a rasping organ called radula with transverse rows of chitinous teeth for feeding (radula is absent in bivalves).
(viii) The sense organs are tentacles, eyes and ospharidium (to test the purity of water and present in bivalves and gastropods).
(ix) Excretory organs are nephridia.
(x) Open type of circulatory system is seen except for cephalopods such as squids, cuttle fishes and octopuses. Blood contains haemocyanin, a copper containing respiratory pigment.
(xi) Development is indirect with a veliger larva.
(xii) eg. Pila (Apple snail).