Category Plants & Animals

          Most amphibians lay their eggs in water. Frogs’ eggs are called spawn. They are protected from predators by a thick layer of jelly. Inside this a tadpole develops. When it hatches out, it is able to swim, using its long tail, and breathes through gills. As the tadpole grows, first hind legs and then fore legs begin to grow. Lungs develop, and the young frog is able to begin to breathe with its head above water. Gradually, the tail shortens until the young frog resembles its adult parents.

          In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs, toads, and newts all hatch from the eggs as larvae with external gills but it will take some time for the amphibians to interact outside with pulmonary respiration. Afterwards, newt larvae start a predatory lifestyle, while tadpoles mostly scrape food off surfaces with their horny tooth ridges.

          Metamorphosis in amphibians is regulated by thyroxin concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts its effect. Specific events are dependent on threshold values for different tissues. Because most embryonic development is outside the parental body, development is subject to many adaptations due to specific ecological circumstances. For this reason tadpoles can have horny ridges for teeth, whiskers, and fins. They also make use of the lateral line organ. After metamorphosis, these organs become redundant and will be resorbed by controlled cell death, called apoptosis. The amount of adaptation to specific ecological circumstances is remarkable, with many discoveries still being made.

          Egg Stage: Amphibian eggs are fertilized in a number of ways. External fertilization, employed by most frogs and toads, involves a male gripping a female across her back, almost as if he is squeezing the eggs out of her. The male releases sperm over the female’s eggs as they are laid. Another method is used by salamanders, whereby the male deposits a packet of sperm onto the ground. The female then pulls it into her cloaca, a single opening for her internal organ systems. Therefore, fertilization occurs internally. By contrast, caecilians and tailed frogs use internal fertilization, just like reptiles, birds, and mammals. The male deposits sperm directly into the female’s cloaca.

          Larval stage: When the egg hatches, the organism is legless, lives in water, and breathes with gills, resembling their evolutionary ancestors (Fish). During the larval stage, the amphibian slowly transforms into an adult by losing its gills and growing four legs. Once development is complete, it can live on land.

          Toads and frogs are similar in many ways, although toads usually have rougher, drier skins and may waddle rather than hopping as frogs do. Some toad spawn is produced in strings, like necklaces, rather than the mass of eggs laid by a frog. While these little amphibians might look very similar at first glance, there are actually a plethora of key differences between them. Frogs and toads may seem similar, but they are quite different. There are many physical differences, such as differences in skin, color, and body type. There are also differences in behavior. A frog will need to be in close proximity to a body of water, for instance, while a toad can be further away. Frogs also tend to hop higher than toads.

          If there was ever a tell-tale sign to indicate which amphibian you are looking at, it’s the texture of their skin. Toads are warty-looking, covered in little lumps and bumps, while Frogs are sleek and smooth. Toads also virtually always have dry skin, whereas frogs look wet even when they are out of the water.

          If you’ve spotted an amphibian making its way along a pavement or ambling through some grass, chances are it’s a toad. Toads cope much better with dry conditions than frogs, as their skin is more waterproof. Frogs lose moisture a lot more easily, and so are rarely seen too far away from water, which explains why they always look moist.

          Frogs have long legs, longer than their head and body, which are made for hopping. Toads, on the other hand, have much shorter legs and prefer to crawl around rather than hop. Frogs are lithe and athletic-looking, whereas toads are somewhat squat and dumpy. Their faces are different too; frogs have a pointed nose while toad noses are much broader. Spawn is another key indicator for which species you’re looking at. Frog spawn is laid in gooey clumps, whereas toads spawn floats in stringy lengths. Like their adult counterparts, frog tadpoles are slimmer whereas toad tadpoles are chunky. Frog tadpoles are also covered in gold flecks, while toad tadpoles are plain black in colour.

Picture Credit : Google

          Amphibians have different life cycles. Many live mainly on land, but most of them spend at least some of their lives in water. Frogs, toads, newts and salamanders are all amphibians. Frogs and salamanders are able to breathe through their damp skins to a certain extent, both in the water and on land, but toads must rely largely on their lungs and cannot remain in water for long.

          Amphibians! In order for water-dwelling animals to adapt to life on land, many new adaptations had to take place. First, they needed to be able to breathe air instead of obtaining oxygen from water. And fins don’t work well as legs! They needed to be able to move around well on land.

          What group of animals begins its life in the water, but then spends most of its life on land? Amphibians! Amphibians are a group of vertebrates that has adapted to live in both water and on land. Amphibian larvae are born and live in water, and they breathe using gills. The adults live on land for part of the time and breathe both through their skin and with their lungs as their lungs are not sufficient to provide the necessary amount of oxygen.

          There are approximately 6,000 species of amphibians. They have many different body types, physiologies, and habitats, ranging from tropical to subarctic regions. Frogs, toads, salamanders, newts, and caecilians are all types of amphibians.

          Most amphibians live in fresh water, not salt water. Their habitats can include areas close to springs, streams, rivers, lakes, swamps and ponds. They can be found in moist areas in forests, meadows and marshes. Amphibians can be found almost anywhere there is a source of fresh water. Although there are no true saltwater amphibians, a few can live in brackish (slightly salty) water. Some species do not need any water at all, and several species have also adapted to live in drier environments. Most amphibians still need water to lay their eggs.

          A very few fish give birth to live young, but most lay their eggs in the water, which is called spawning. A fish may lay millions of eggs, only a small proportion of which will grow into adults. A few fish, such as salmon and sticklebacks, build nests underwater to protect their eggs. They lay fewer eggs because more young survive. Dogfish and skates protect their eggs in black capsules. The empty capsules are often washed up on the beach, and it is these that are known as “mermaid’s purses”.

          Perhaps you’ve found a “mermaid’s purse” on the beach. Mermaid’s purses blend really well with seaweed, so you may also have walked right by one. Upon further investigation, you can learn more about what they are. The enchantingly named structures are the egg cases of skates and some sharks. This is why they are also known as skate cases.

          While some sharks bear live young, some sharks (and all skates) release their embryos in leathery egg cases that have horns and sometimes long tendrils at each corner. The tendrils allow them to anchor to seaweeds or other substrates. Each egg case contains one embryo. The case is made up of a material that is a combination of collagen and keratin, so a dried egg case feels similar to a fingernail. 

          In some areas, such as in the Bering Sea, skates seem to lay these eggs in nursery areas. Depending on the species and sea conditions, the embryo may take weeks, months or even years to fully develop. When they hatch out of one end, the baby animals look like miniature versions of their skate or shark parents. 

          If you find a mermaid’s purse on the beach or are lucky enough to see a “live” one in the wild or in an aquarium, look closely — if the developing skate or shark is still alive, you may be able to see it wiggling around. You also may be able to see it if you shine a light through one side. The egg cases on the beach are often light and already opened which means the animal inside has already hatched and left the egg case. 

          Mermaid’s purses usually get washed or blown to the high tide line of the beach, and they often get wrapped up in (and blend in well with) seaweeds and shells. As you’re walking along the beach, walk in the area where shells and ocean debris seems to have washed up, and you might be lucky enough to find a mermaid’s purse. You may be more likely to find one after a storm. 

 

          All sharks are carnivorous (meat-eaters), and a few species, such as the white shark, which can grow to 9m (30ft), have been known to attack humans or even boats. But 90% of all shark species are not dangerous to humans at all.

          The United States averages just 16 shark attacks each year and slightly less than one shark-attack fatality every two years. Meanwhile, in the coastal U.S. states alone, lightning strikes and kills more than 41 people each year.

          Each year there are about 50 to 70 confirmed shark attacks and 5 to 15 shark-attack fatalities around the world. The numbers have risen over the past several decades but not because sharks are more aggressive: Humans have simply taken to coastal waters in increasing numbers.

          Over 375 shark species have been identified, but only about a dozen are considered particularly dangerous. Three species are responsible for most human attacks: great white (Carcharodon carcharias), tiger (Galeocerdo cuvier), and bull (Carcharhinus leucas) sharks.

          While sharks kill fewer than 20 people a year, their own numbers suffer greatly at human hands. Between 20 and 100 million sharks die each year due to fishing activity, according to data from the Florida Museum of Natural History’s International Shark Attack File. The organization estimates that some shark populations have plummeted 30 to 50 percent.

          The shortfin mako (Isurus oxyrinchus) is often recognized as the world’s speediest shark. It has been clocked at speeds of up to 20 miles an hour (32 kilometers an hour) and can probably swim even faster than that. Makos are fast enough to catch even the fleetest fish, such as tuna and swordfish.

Picture Credit : Google

          Of course, it is the female seahorse that is the real mother, producing and laying eggs. The difference is that she lays the eggs in a special pouch on the male seahorse’s body. The babies develop inside the pouch and emerge when they are fully developed. As they emerge, it looks as though they are being born from the male seahorse.

          Seahorses and their close relatives the pipefish and the seadragons are very unusual, because it is the males that get pregnant and give birth to the babies. Instead of growing the baby seahorses inside their belly in a uterus, like human mums do, the seahorse dads will carry the babies in a pouch, a bit like a kangaroo’s pouch.

          To produce babies, seahorses have to mate first. Seahorse mating is really beautiful. Males and females dance around one another and flutter their fins, and they may dance together over several days before they actually mate.

          When they’ve decided they like each other, the seahorse females swim towards the surface of the water, and the males follow. The females then put their bright orange eggs into the pouch of the males through the hole at the top of the pouch. Once the eggs are safely inside, the males will add their sperm and shut the opening. The eggs are fertilized by the sperm, and then start developing into baby seahorses.

          With that, the job of the seahorse mum is done! She swims off, and leaves the father to take care of the growing babies. Inside the pouch, the babies grow eyes, tiny snouts, and little tails. It takes about 20 days for the babies to develop, safely tucked away from other animals that might want to eat them.

Picture Credit : Google