Respiratory organs in aquatic arthropods like crayfish,prawn and molluscs like $Unio$ are

Which of the following is not a character of a respiratory surface?

Given below are four matchings of an animal and its kind of respiratory organ:
$1.$ Silver fish - trachea
$2.$ Scorpion - book lung
$3.$ Sea squirt - pharyngeal gills
$4.$ Dolphin - skin
Choose the correct option.

Which group of animals respire through lungs?

Select the correct option regarding the respiratory organs in different animals:

Which of the following statements is correct?