Question

Book lungs are respiratory organs of
A. Mollusca
B. Arachnida
C. Mammals
D. Aves

Answer 1

Hint: A type of respiratory organ that consists of a series of plate-like hemolymph-filled structures are known as book lungs. They help in atmospheric gas exchange and are commonly found in organisms that do not have antennae and have eight legs.

Complete answer: Book lungs are a type of respiratory organ in arachnids such as spiders, and scorpions. They are present within small openings in the abdominal region of the arachnids. Plate-like structures are filled with haemolymph and between these plates, some air-spaces allow air circulation around the plates. They are known as book lungs because of their stacked-plate appearance resembling closed pages of a book. These stacked plates are extended into an internal pouch that is formed by the exoskeleton that opens into the external environment by a small slit. Plates provide an increased surface area for the exchange of oxygen and carbon dioxide with the surroundings. Four pairs of book lungs are found in scorpions and two pairs are found in spiders. The book lungs are located inside the arachnid arthropods. It is filled with hemolymph that carries oxygen.
Hence, the correct option is B-Arachnida.

Note: Book lungs are found inside the ventral abdominal cavity that connects with the surrounding through an opening. These lungs are not related to the lungs of modern-dwelling vertebrates. The folds of the book lungs help in increasing the surface area of gaseous exchange. In most of the species, movement of lungs is not required.