• Notochord is present only in embryonic stages and in adults, it is replaced by vertebral column or backbone.
• The heart is ventrally placed and is usually with hepatic portal system.
  
• The excretory organs are paired kidneys.
• Skin is covered by a protective skeleton which consists of lateral appendages, hair, feathers etc.

• In vertebrates, notochord is present only in embryonic stages and then it is replaced by a vertebral column or backbone.
• In chordates, notochord is present throughout the life of the organism.

Vertebrata is a class of organisms containing notochord and vertebral column.

A. RBCs or the red blood cells contain a red coloured pigment due to the presence of iron) called haemoglobin which carries oxygen to different parts of the body.

Vertebrates are the organisms which are characterized by the presence of the nerve cord. Vertebrates have the dorsal hollow nerve cord. This nerve cord develops into the central nervous system.
All vertebrates have a ventrally placed heart. The heart may be 2,3 or 4 chambered. Most of the organisms have closed circulatory system.
All vertebrates have a body cavity with alimentary canal. The alimentary canal starts at the mouth and ends at anus. 

• Vertebrates are animals that have a backbone or spinal column, also called vertebrae.
• The five most well-known classes of vertebrates are mammals, birds, fish, reptiles, amphibians. They belong to the phylum Chordata.
  

The vertebral column, also known as the backbone or spine, is a bony skeletal structure found in vertebrates. It is formed from individual bones called vertebrae, which houses the spinal canal, a cavity that encloses and protects the spinal cord. Therefore, (d) is the correct answer. 

All chordates are characterised by three primary chordate features the presence of a notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits. The notochord, later on, gives rise to a bony vertebral column, which surrounds and protects the spinal cord. So, the correct answer is option B.

All vertebrates have a living endoskeleton. The characteristic of vertebrates without exception is the presence of a brain. The brain is set inside a bony box called as the cranium. Cranium is made up of eight bones. It protects the human brain from mechanical injury.
Therefore, the correct answer is option B.

• The heart of vertebrates is ventrally placed.
• The body of vertebrates consists of serially arranged vertebrae which comprises of a major part of their axial exoskeleton, the vertebral column or the backbone.
• The coelom of vertebrates is large and well developed and it is of enterocoelous type.

• The heart pumps only impure blood in sharks. Sharks have a two-chambered heart which is an S-shaped tube. It has an atrium and ventricle. The blood is pumped by the heart through the afferent branchial arteries to capillaries in the gills, where the blood is oxygenated). 
• The blood then flows through efferent branchial arteries, through the tissues of the body, and back to the heart in veins. Sharks have low blood pressures; the walls of the pericardium are rigid, creating suction within the pericardium to maintain the flow of blood. To circulate blood throughout their bodies, many sharks must swim continuously. 
• The blood flow is similar to humans because blood is pumped by the heart to the rest of the body by arteries and returned to the heart by veins. 
• A difference is that humans have 4-chambered hearts while sharks only have two chambers.

Viviparous sharks give birth to live young. The number of pups in a litter ranges from 2-20 or more. For example, the Bull sharks, Whitetip reef shark, Lemon shark, Blue shark, Mako, Porbeagle, Salmon shark, the Silvertip shark, and Hammerheads.

Herdmania is an ascidian urochordate.

Because they are supposed to be associated with the function of excretion just like liver.

Echinodermata and all chordates are deuterostome and enterocoelous.

(A) Cyclostomes - Agnatha