The term 'snail' is a commonly used to refer to all molluscans that belong to the class Gastropoda. The common characteristics of the class highlight coiled shells. The term snail applies to sea, land, and freshwater snails, the epithets referring to the habitat. The ones without shells are called slugs, while those that flaunt broad and conical-shaped uncoiled shells are called limpets. Snails are known to adapt to various habitats and take on the form and behavior accordingly. The subsequent changes in their anatomy make it difficult to draw common assumptions on behavior patterns and physical characteristics.
Snails are found in the sea, ditches, fresh and brackish water, deserts, and diverse terrestrial terrain. In comparison to other varieties, snails that are found in abyssal sea contours are greater in diversity and also in biomass. They can be herbivorous, carnivorous, as well as omnivorous. They move on muscular feet lubricated by mucus. They are known to move very slowly, literally at 1 mm/second. They have a special tissue layer that protects and covers their internal organs. This mantle is attached to the outer shell.
The Life Cycle
Terrestrial snails produce spermatozoa as well as ova. In the case of freshwater snails and marine species like periwinkles, distinctly identifiable genders are present. They mate by the time they are a year old. The ritual courtship prior to mating can last for anything between two and ten hours. They inseminate each other and fertilize the ova. Slugs and land snails have a reproductive opening on one side for sperm exchange. Immediately after fertilization, the eggs begin to develop. Hybridizations and parthenogenesis are not uncommon in snails. There are some, especially in the freshwater category, that carry the eggs within themselves until they hatch.
The eggs are protected in a warm and damp environment, usually dug 10 cm below the top soil. The sizes of the eggs differ according to the species, and range between 3 mm to 6 cm in diameter. They hatch within 4 weeks and the young molluscans emerge. Snails are known to lay eggs at least once a month.
The outer shell of the egg develops even as it fertilizes. Though the embryo has a shell that is weak from the lack of calcium, the formation makes the young snails most distinguishable. The calcium content for the development of the shell is obtained by eating the eggshell on emerging. Research reveals that newly hatched snails even cannibalize other unhatched eggs. At this stage, they appear transparent, almost colorless. Thereafter, regular feeding generates the first show of color. At this point in time, the young snails look like miniature versions of the adults. They feed and grow consistently for the next three years, and finally attain adult size. The growth process is fast, and many even beat their parents with regard to size.
Different types of snails have different lifespans. The wild Achatinidae live for about 7 years, while aquatic apple varieties live barely for a year. These molluscans have shells of calcium carbonate that take on a spiral shape. When a snail secretes mucus to build a thick structure around the shell opening, it is a sign that the growth process has ceased and reproduction is in focus.
Snails have either one or two tentacle pairs on the head. The ommatophores or eye stalks are the upper formations, while the lower tentacles function as olfactory organs. They are completely retractable. Snails consume anything from leaves and vegetables, to algae, plankton, and other microscopic organisms. A threat to their existence comes in the form of parasites. They succumb to natural predators such as decollate snails, leeches, and beetles. The parasitic worm Leucochloridium paradoxum affects the retracting of the eye stalk, making the creature vulnerable to birds of prey. Today, environmental pollution and terrestrial encroachment are leading to the extinction of this species.