Limpets are any of the species of gastopods assigned to the taxonomic Order Docoglossa. Even though the limpet can be a very small creature it has incredible abilities. It is hard to imagine that something so small can be a help to the marine environment, but it is. Also the abilities it has to return to its home after feeding is just amazing. Humans have a big effect on limpets. Because limpets have been a major component in the diet of aboriginal, the limpets are decreasing in size in many locations. 
All Patellogastropods have an oval cap-shaped shell, which is sculpted with concentric growth lines. In many species, additional radial ribs extend from the apex to the shell margin. These ribs may be very fine like growth lines or broad and strongly raised off the surface. The inner surface of the shell bears a horse-shaped muscle scar that opens anteriorly near the head. The head has one pair of tentacles and a mouth. Inside the mouth is a radula, which has few teeth that are brown in color because of the presence of iron compounds. The Patellogastropod also has a gill that is located around the edge of the foot and extends around the aperture, which is a opening or a hole. The foot of the Patellogastropod is broad and muscular which is adapted to cling to rocks and other hard substrata in the water.
The limpet can range in size from about 0.19-7.8 inches. The smallest species and the largest are typically found in the lowest intertidal zone or subtidally. The color of the shell of the subtidal species are typically white or pink in color and intertidal species are typically drab brown or gray with white spots and radial rays. Coloration of the shell of the limpet is dependent on their diet, and often the shell is similar in color to the substrata on which the limpet occurs because of the incorporation of plant compounds into the shell.
Unlike other gastropods, limpets have separate sexes, but some are hermaphrodites. The limpets start out as a male but many change into females as they age. There are two types of males, true males and temporary (protandic) males. Once a year, usually early on during the winter, the female limpets discharge eggs while the male limpets discharge their sperm into the sea. The eggs are fertilized in the sea and then are carried away by the currents. The larvae then hatches and is joined to plankton. At this stage, the larva is feeding on microscopic algae. Later on in the year the larvae settle and mature into adult limpets.
Limpets have good effects on their environment. They keep their environment clear of algae. At night limpets graze on algae. They feed by using their radula, which is forced out of the mouth and is used to scrape the algae. Because algae grows on hard surfaces, the limpet's radula wears away, and that is the reason why the radula is continually growing. When limpets are grazing, they display a homing instinct, by producing a trail of slime. After grazing they follow the trail back to the same spot, where they eventually gouge indentations in a rock. These indentations are even seen in hard Cornish Rock. If the rock is hard, instead of wearing away the rock, the edge of the shell is abraded. The deep water species of limpets feed on detritus, unlike most species which live intertidally and feed on algae.  Predators of patellogastropods include predatory gastropods, sea stars, nemertean worms, fishes, lizards, small mammals, and shore birds. Shore birds such as oystercatchers are especially voracious predators and can remove limpets in such numbers that entire expanses of the intertidal can become green from algal growth due to the lack of limpet feeding. 
Most patellogastropods are dioecious (have seperate sexes), but there are some who are hermaphrodites. There is no courtship or mating between patellogastropods, because the males and females release their sperm and eggs into the sea and fertilization occurs externally.
Many patellogastropods are very protective of their territories. Their territories are dependent on the specific food reserves were patellogastropods feed. When the limpets are protecting their territory, they become highly aggressive by using their shells as battering rams to drive both conspecifics and other herbivorous species from their territory. Territorial species are often larger than related non-territorial species, and many territorial species are also protandric hermaphrodites—beginning life as males before becoming females—often upon the acquisition of a feeding territory.
Activity patterns of patellogastropods are often complicated. At high tide, moving limpets are susceptible to aquatic predators such as fish and crabs. At low tide, species are especially vulnerable to shore birds and foraging mammals. Moreover, low tide also places intertidal patellogastropods under physiological stress due to the effects of drying. Many species are most active at night during low tide when visual predation is less effective. Migratory movements of patellogastropods are limited to a general up-shore pattern, with recruitment occurring in the lower intertidal and later movement leading to life in higher intertidal zones.