Some species of snails have a second 'door' on the shell, called an operculum, in addition to the main exit from which the foot muscle protrudes. During development, the body of the snail gets twisted degrees counter-clockwise inside the shell. This causes the anus of the snail to become situated directly over top of its head! The use of 'love darts' during mating appears to have evolved not for reproductive reasons, but rather as courtship behaviour.
Young freshwater snails look like smaller versions of adults. They have shells throughout their development, and are never without one. Some snail species, such as those in marine environments, lay fertilized eggs.
Others, such as freshwater snails, give birth to live young. Aquatic snails develop quickly and mate while they are young in order to make up for not having a larval stage.
The males often have a mating organ, a penis, or a tentacle, that is used to deliver the sperm to the female. Gastropods often take part in courtship to win the affection of a mate.
Some terrestrial gastropods 'shoot' what are called 'love darts' at their potential mate. Females of some species can also reproduce by a process called 'parthenogenesis', which means they fertilize their own eggs. Scientists believe this mating behaviour evolved so that the organism could still reproduce in regions where mates were scarce.
Snails are a highly sought-after food source for many predators. The predators can be divided into two different groups: the shell crushers and the shell invaders. Shell-crushing predators include some bigger species like pumpkinseed sunfish and mud minnows.
These species are strong enough to use their teeth to crack open snail shells and eat the snail inside. Some crayfish can use specialised appendages, called 'mandibles', to break the shells. Shell-invading predators include smaller crayfish, leeches, and giant water bugs. These organisms are not strong enough to crush shells. Instead, they eat the snails by pulling them out of their shells. To avoid being eaten, snails will build the hardest shells possible. Snails, famously, live in a mobile home that is produced by an organ called the mantle, a thin layer of multi-tasking tissue that secretes the limey material that hardens into the shell.
Shells are heavy, relatively speaking, which is why snails move slowly. Not all ponds welcome snails equally—water that is soft or is acidic dissolves snail shells, but snails that live in calcium-rich water grow thicker shells. Gilled snails secrete a characteristic horny plate called an operculum on the nether end of the foot, and when they pull their body into their shell, the operculum forms a door that seals the shell against dehydration or enemies.
Fish love to eat snails, and the opercula in fish stomachs allow Operculum Experts to determine what kinds of snails the fish are eating. Aquatic snails have two tentacles and land snails have four, with the eyes located at their tips land snails or at their base aquatic snails. Snails depend on their senses of smell and touch and on chemosensory organs to navigate their world. There are anything between 85, and , mollusks of which percent are gastropods.
Therefore, the world is home to more than 60, species of them. Land snails range greatly in size. While some of them are only a few inches long and often weigh only a few ounces, there are land snails that reach almost 12 inches, like the Giant African Land Snail, a species endemic to Africa.
Certainly, land snails are incredibly slow. Their forward speed depends on the species, but usually, it is between 0. Its slowness is another feature that has made it famous, and some people have known how to play with it. For example, in many places in the UK, snail racing is organized! Can you imagine waiting for them to reach the finish line? It does not last as long as it may seem.
While moving, snails leave behind a trail of slime, a lubricant they produce to allow them to go on any terrain without injuring its body. They use their sense of smell to help them find food being their most important sensory organ.
You will find that snails are most active at night. They may come out during the early morning hours as well. The biological features of snails are fascinating.
For example, most are hermaphrodites, which means that a single snail has male and female reproductive organs at the same time. A few weeks after mating and laying eggs, the hatchlings emerge from their egg, small and defenseless against many predators that sneak around, such as beetles, birds, turtles and even other snails. There are exceptions. Some species have sex differentiation, so every individual is either male or female.
The life expectancy of snails in the wild is about 3 to 7 years, but in captivity, they can live up to years or even more. Snail shell is made of calcium carbonate and keeps growing as long as the snail grows. They keep adding more calcium carbonate to the edge until the snail reaches adult size. Humans have eaten land snails for centuries, although not everywhere.
0コメント