There are different types of receptors in animals depending on their structures and response to stimuli. These are as follows.
1. Rheoreceptor of fishes and aquatic amphibians are stimulated by water currents. In fish, the lateral line is a sense organ used to detect movement and vibration in the surrounding water. The receptors in the lateral line are neuromasts. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail. Sometimes parts of the lateral organ are modified into electroreceptors, which are organs used to detect electrical impulses. It is possible that vertebrates such as sharks use the lateral organs to detect magnetic field as well. Most amphibian larvae and some adult amphibians also have a lateral organ.
2. Olfactoreceptors: The sense of smell is dependent upon the presence of olfactory neurons, called olfactoreceptors, in the olfactory epithelium of the nasal passages among the vertebrates.
3. Photoreceptors: Photoreceptors are structures, which are sensitive to light and in some instances are also capable of perceiving form, that is, of forming images. Light-sensitive structures include the stigma of phytomonads, photoreceptor cells of some annelids, pigment cup ocelli and retinal cells in certain asteroids, the eye-spot in many turbellarians, and the ocelli of arthropods. The compound eye of arthropods, molluscs, and chordates is capable of image formation and is also photosensitive.
4. Gustatoreceptors: The sense of tase is mediated by the taste buds, or gustatoreceptors. In most vertebrates these taste buds occur in the oral cavity, on the tongue, pharynx and lining of the mouth; however, among certain species of fish, the body surface is supplied with taste buds as are barbels of the cat fish.