The Creation Wiki is now operating on a new and improved server.
Snail
From CreationWiki, the encyclopedia of creation science
Grace Lackey (Talk | contribs) (→Ecology) |
Grace Lackey (Talk | contribs) (→Land Snails) |
||
| Line 48: | Line 48: | ||
[[File:example.jpg|thumb|150px|left|Description]] | [[File:example.jpg|thumb|150px|left|Description]] | ||
===Land Snails=== | ===Land Snails=== | ||
| - | + | Terrestrial snails can live in virtually any habitat from harsh deserts and mountain climates, to swamps and gardens. Some species are known as anthropophilic (they are mostly found around human-inhabited areas). Snails that live in the desert or anywhere else dry can stay in their shells for up to two years. This is a state called estivation; its like hibernation, but its triggered by dry and hot conditions instead of cold. They will remain sealed in their shell until the water is replenished [http://lawrencehallofscience.org/foss/fossweb/teachers/materials/plantanimal/landsnails.html]. Snails in those kinds of habitats usually have thick shells. Snails that dwell in moist enviroments tend to have thinner shells. | |
| - | + | ||
===Aquatic Snails=== | ===Aquatic Snails=== | ||
Revision as of 21:05, 22 November 2009
Please do not edit the article until this banner is removed.
| Snail |
|---|
|
| Scientific Classification |
|
| Selected Snails |
| * [[]] |
| Image Description |
|
Contents |
Introduction
Write this section last...
Anatomy
Shell
All snails are univalves (they have a single shell used for protection and shelter). There are over 75,000 species of snails, so obviously the shapes of the shells are diverse. A strong muscle connected to the columella holds the snail’s shell onto the body. Composition: Snail shells are made almost completely of calcium carbonate (97.5 %). Calcium phosphate and silicate, magnesium carbonate and oxide, iron, manganese oxide and other organic substances make up the rest of the composition. Appearance: [1]Most shells have a conical or oval shape. All shells have twists known as whorls, which are widest at the base of the shell and get progressively tighter as they spiral towards the center. The newest whorl, also known as the body whorl, is at the base; any spirals above it are jointly known as the spire. The apex (tip) is at the center. All whorls are clearly separated by a groove dubbed the suture. An aperture (opening) in the body whorl has an inner-lip and outer-lip. New material added to the lips increases the size of the shell. Some snails appear to have ridges on their shells. These wrinkles result from the variation in growth rates; due to environmental conditions, the shell will grow thicker in some places (during warm months), and much thinner elsewhere (in colder months). The ridges are known as axial ribs. Growth: Even before the snail hatches, it has formed a single small whorl around itself known as a protoconch. As the snail grows, new material is secreted by the mantle. The mantle lines the inside of the bottom whorl. In order to form the spiral shape, it must have a central rod for support. Such a rod is called a columella; it goes all the way through the center of the shell. Purpose: If the snail feels threatened, it can draw back into its shell for defense. They use a trap-door like plate called an operculum to seal off the opening. Snails also reside in their shells during overly-hot or -cool weather to keep from drying out.[2]
Land Snails
The snail has a few basic structures such as the foot, head, shell and visceral mass. Only the head and foot are visible; the visceral mass includes internal organs housed within the shell. Internal organs include a lung, the digestive system, the kidney, liver and the reproductive system. They also have a nervous system running throughout the body, but concentrated mostly in the head [3]. Depending on the species, a snail will have one to two retractable pairs of tentacles on its head. The eyes are always located on the longer of the two pairs [4]. Snails have a four-part brain capable of learning. Scientific research has shown that snails are actually quite smart; they possess associative thinking based on experience and conditioning [5]. Snails move by a kind of locomotion called reptation [6]. The snail’s foot helps it move by secreting mucus from a gland near the mouth. Without this mucus trail, the snails would risk injury of sharp objects and the environment would be too rough for their soft bodies to move across. But with the mucus, snails can crawl across things like knives and needles. Unlike slugs, the snail’s slime trail is spotty instead of continuous. A snail’s foot is also protected by the mantle. The mantle is also found around the shell. When snails move, they often seem overtaken by spasms. These tremors are actually caused by the contraction and expansion of the muscles in the foot. By creating a rippling motion along the foot, a snail can push and pull itself along any surface [7]. Despite their slowness, there is a recurring cadence when they move [8]. Terrestrial snails breathe using a lung found in the mantle cavity[9]. The mantle cavity also holds the heart and the kidney.
Gilled Snails
Sea snails breathe using gills, just like a fish does. The gills, like land snail’s lungs, are located in the mantle cavity. Fresh-water snails may also have gills, but many have lungs and must surface to get oxygen [10]. Unlike land-dwelling snails, a marine snail’s eyes are placed at the base of the tentacles and cannot move. [11].
Reproduction
Snails are hermaphroditic (contain both male and female reproductive organs). Even so, most snails mate in order to produce eggs. Since a snail’s lifespan does not usually last more than five to seven years, snails are considered sexually mature once they are one year old [12]. Mating takes place during late spring to early summer; occasionally there will be a second mating during summer. Depending on the climate, snails may mate as late as October and a second time two weeks later. Snails can act as one gender in a season and the other gender next season. They can also play both roles at once and fertilize each other at the same time [13]. Before mating, snails put on a mating ritual which can be two to twelve hours long. After this ritual, the snails will fertilize each other’s eggs. Snails can store the sperm for up to a year, but typically lay eggs within a couple of weeks. There can be up to 100 eggs. After the eggs are fertilized, they are buried in the soil (or beside a hard area, like a rock, for marine species) and begin to develop inside the embryo. Within two to four weeks, the tiny snails have hatched. Their shells are still very weak, so in order to obtain calcium, they eat their own egg – or even another snail’s egg. They stay within the nest for a few months until they develop fully [14]. A few species of snails (mostly fresh-water) actually give birth to live young, but the majority lay eggs. Other snails also reproduce by broadcast-spawning by releasing the sex cells into the water. If the cells are released close enough to another cell, the sperm fertilizes the egg and embryonic development begins [15].
Ecology
Land Snails
Terrestrial snails can live in virtually any habitat from harsh deserts and mountain climates, to swamps and gardens. Some species are known as anthropophilic (they are mostly found around human-inhabited areas). Snails that live in the desert or anywhere else dry can stay in their shells for up to two years. This is a state called estivation; its like hibernation, but its triggered by dry and hot conditions instead of cold. They will remain sealed in their shell until the water is replenished [16]. Snails in those kinds of habitats usually have thick shells. Snails that dwell in moist enviroments tend to have thinner shells.
Aquatic Snails
Other
Gallery
Common-name |
Common-name |
Common-name |
Common-name |
 Browse |
References
- reference title author, publisher, date.
- reference title author, publisher, date.
- reference title author, publisher, date.
