In Urochordata, notochord is present only in larval tail, while in Cephalochordata, it extends from head to tail region and is persistent throughout their life.

Annelids have closed circulatory system and excretory organs are nephridia. Nephridia are present in each segment.

Ascariasis: People become infected when they eat food or drink water that contains the eggs of the roundworm Ascaris lumbricoides.

In bilateral symmetry, the body can be divided into identical left and right halves in only one plane.

Differences between the direct and indirect development are as follows.
Direct development : In case direct development the life cycle of an adult individual lacks any larval stage in its life cycle. The adult give rise to young ones which directly develop into the adult.e.g, mammals
Indirect development : It is present mostly in case of lower animals, the adult individual gives rise to eggs mostly which develop into the adult after being passing through serval larval stages, e.g, echinoderms Ascaris, cockroach have prolonged larval stages in their life cycle.

Parasitic platyhelminthes have a thick cuticle.They lack alimentary canal and absorb the nutrients directly through their body surface.Some parasites are provided with hooks and suckers.

Mammals are unique due to following features
(i) Presence of milk-producing mammary glands in females
(ii) Hairs present on the whole body

Digestive system having only a single opening to the outside of the body that serves as both mouth and anus, called incomplete digestive system while a complete digestive system has two separate openings, i.e mouth and anus.

The empty space in pneumatic bones helps in weight reduction of skeleton in birds.It is a kind of flight adaptation in birds

This is because it supplies deoxygenated blood to gills for oxygenation

Obellia,shows alternation if asexual and sexual phases in its life cycle.

Porococytes line the spongocoel in Sycon.

Porifera

Most bony fishes have cycloid or ctenoid scales. Both cycloid and ctenoid scales consist of an outer layer of calcium and an inner layer of connective tissue.

In the animal kingdom, there are two broad phyla that exhibit radial symmetry: One of these is cnidaria, which include jellyfish, anemones, and corals. Jellyfish exhibit radial symmetry in four points around its center. The other phylum is echinodermata, such as sea stars, urchins, and sea cucumbers.

Flight adaptations found in birds
(i) Body is streamlined to reduce air resistance during flight
(ii) Forelimbs are modified into wings
(iii) Wings have long quill feathers to increase the efficiency of beating of wings
(iv) Pneumatic bones are present to reduce the body weight
(v) High metabolic rate to provide energy for flight
(vI) Air sacs present in lungs help in double respiration

Differences between lizards and snakes

The difficulties that will be faced if common fundamental features are not taken into account are as follows
(i) The interrelationship among different animals cannot be traced.
(ii) The picture of all animals at a glance cannot be projected
(iii) The development of other animal species cannot be made.
(iv) There are numerous animal species which show great variety of life. The various common fundamental characters are taken into account for the classification of these animals. If this has not been separately at individual level. Therefore, a classification has to be based on the common fundamental characters for the sake of study of diversity in living forms.

One has to follow the following steps to classify a specimen
(i) Level of organisation
(ii) Body symmetry
(iii) Segmentation pattern.
(iv) Presence or absence of vertebral column
(v) Locomotory organelles limbs/fins/wings.
(vi) Patterns of organ system like digestive, circulatory or reproductive system.

Differences between Chordates and Non-Chordates are given below

Birds have undergone many structural adaptations to suit their aerial life. Some of these adaptations are as follows.
1. Streamlined body for rapid and smooth movement. Vertical air movements help the bird with gliding and soaring in the air.
2. Covering of feathers for insulation.
3. Forelimbs are modified into wings and hind limbs used for walking, perching, and swimming.
4. The presence of pneumatic bones reduces weight.
5. They have a higher metabolic rate that provides the energy for flight.
6. Presence of additional air sacs to supplement respiration.
7. The sternum is modified into a keel for the attachment of large, powerful flight muscles.

Differences between poly and medusa are

The body wall of a common sponge consists of three layers which are
(i) Pinacoderm (dermal layer) It is an outer cellular layer which consists of 
(a) flattened pinacocytes
(b) oval porocytes
(ii) Choanoderm (gastral layer) It is inner cellular layer consisting of highly specialised flagellated cells called choanocytes or collar cells.
(iii) Mesoglial layer (mesenchyme) It is a non-cellular layer found in between pinacoderm and choanoderm.It has fine dispersed spongin fibres and numerous spicules.It also contains amoebocytes of both pinacoderm and choanoderm.
Amoebocytes are modified into following cells
(a) Archaeocytes (totipotent cells)
(b)Trophocytes (nurse cells)
(c) Thesocytes
(d)Gland cells
(e)Collencytes
(f)Myocytes
(g)Germ cells
(h)Chromocytes
(i)Phagocytes