The Salamander

Jan 30, 2011 Features / Columnists, Interesting Creatures in Guyana

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Salamander is a common name of approximately 500 species of amphibians. They are typically characterised by their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant species are grouped together as the Urodela.
Most salamanders have four toes on their front legs and five on their rear legs. Their moist skin usually makes them reliant on habitats in or near water, or under some protection (e.g., moist ground), often in a wetland. Some salamander species are fully aquatic throughout life, some take to the water intermittently, and some are entirely terrestrial as adults. Unique among vertebrates, they are capable of regenerating lost limbs, as well as other body parts.
Mature salamanders generally have a primitive tetrapod body form similar to that of lizards, with slender bodies, long tails, and four limbs. However, like some lizards, many species of salamander have reduced or absent limbs, giving them a more eel-like appearance. Most species have limbs with four toes on the forelimbs, and five on the hind limbs, and lack claws.
Salamanders are often brightly coloured, either in both sexes throughout the year, or only in the males, especially during the breeding season. However, the species dwelling entirely underground are often white or pink, lacking any skin pigment.
Many salamanders are relatively small, but there are definite exceptions. They range in size from the minute salamanders, with a total length of 2.7 centimetres (1.1 in), including the tail, to the Chinese giant salamander which reaches 1.8 metres (5.9 ft) and weighs up to 65 kg (140 lb). Most, however, are between 10 centimetres (3.9 in) and 20 centimetres (7.9 in) in length. Salamanders regularly shed the outer layer of their skin (the epidermis) as they grow, and then eat the resulting slough.
Respiration differs among the different species of salamanders. Species that lack lungs respire through gills. In most cases, these are external gills, visible as tufts on either side of the head, although the amphiumas have internal gills and gill slits. Some salamanders that are terrestrial have lungs that are used in respiration, although these are simple and sac-like, unlike the more complex organs found in mammals. Many species, such as the olm, have both lungs and gills as adults. Some terrestrial species lack both lungs and gills and perform gas exchange through their skin, a process known as valerian respiration in which the capillary beds are spread throughout the epidermis, and inside the mouth. Even some species with lungs can respire through the skin in this manner.
The skin of salamanders secretes mucus, which helps keep the animal moist when on dry land, and maintains their salt balance while in water, as well as providing a lubricant during swimming. Salamanders also secrete poison from glands in their skin, and some additionally have skin glands for secreting courtship pheromones.
Hunting is yet another unique aspect of salamanders. In the lungless salamanders, muscles surrounding the hyoid bone contract to create pressure and actually “shoot” the hyoid bone out of the mouth along with the tongue. The tip of the tongue is composed of a mucus which creates a sticky end to which the prey is captured. Muscles in the pelvic region are used in order to reel the tongue and the hyoid back to its original position.
Many of the highly aquatic species, however, have no muscles in the tongue, and do not use it for capturing prey, while most other species have a mobile tongue, but without the adaptations to the hyoid bone. Most species of salamander have small teeth in both the upper and lower jaws. Unlike frogs, even the larvae of salamanders possess these teeth.
To find their prey, salamanders use trichromatic colour vision in the ultraviolet range based on two photoreceptor types maximally sensitive around 450 nm, 500 nm and 570 nm. Permanently subterranean salamanders have reduced eyes, which may even be covered by a layer of skin. The larvae, and the adults of some highly aquatic species, also have a lateral line organ, similar to that of fish, which can detect changes in water pressure. Salamanders have no external ear, and only a vestigial middle ear.
Salamanders will use tail autonomy to escape predators. Their tail will drop off and wriggle around for a little while, and the salamanders will either run away or stay still enough to not be noticed while the predator is distracted. Salamanders routinely regenerate complex tissues.
Within only a few weeks of losing a piece of limb, a salamander perfectly reforms the missing structure. Their resemblance to lizards is the result of symplesiomorphy, their common retention of the primitive tetrapod body plan, and they are no more closely related to lizards than they are to mammals – or to birds for that matter.
The life history of salamanders is similar to that of other amphibians such as frogs and toads. Most species fertilize the eggs internally, with the male depositing a sac of sperm in the female’s cloaca. The most primitive salamanders – those grouped together as the Cryptobranchoidea – instead exhibit external fertilisation. The eggs are laid in a moist environment, often a pond, but sometimes moist soil, or inside bromeliads.
Some species are ovoviviparous, with the female retaining the eggs inside her body until they hatch. A larval stage follows in which the organism is fully aquatic or land dwelling, and possesses gills. Depending on species, the larval stage may or may not possess legs. The larval stage may last anything from days to years, depending on the species. Some species (such as Dunn’s Salamander) exhibit no larval stage at all, with the young hatching as miniature versions of the adult.

(Source: Wikipedia – The Free Online Encyclopedia)

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