An invertebrate is an animal that does not have a backbone. Option 1 states that an invertebrate does not have a notochord. The notochord is a flexible rod-like structure found in some animals, including vertebrates, that provides support and foundation for the development of the backbone. Since invertebrates don`t have a backbone, it is correct to say that they do not have a notochord.

Option 2 states that an invertebrate does not have a body cavity. However, this statement is incorrect. Invertebrates can have a body cavity, which is also known as a coelom. The coelom is a fluid-filled space that houses internal organs in many invertebrate species.

Option 3 states that an invertebrate does not have a haemocoel. This is incorrect. Invertebrates do have a haemocoel, which is a body cavity filled with blood or hemolymph.

Option 4 states that an invertebrate does not have gills. This is incorrect as well. Some invertebrates, such as certain species of mollusks and crustaceans, have gills for respiration.

Therefore, the correct answer is option 1 - an invertebrate