Next is their skin glands Skin lack hair, scales or any outer covering and contain gland. The skin of amphibians generally is described as being naked, that is lacking the covering scales, feathers, or hair characteristic of most other classes of vertebrates. It is also highly glandular. Amphibian skin is rich in mucous glands and poison glands, secreting substances important for gas exchange and playing a fundamental role in chemical defense against predators and microorganisms. While mucous glands are responsible for the production of the slippery mucus, granular glands are considered the production site of toxins. Its secretion aid in protection. In amphibians, secretions of toxins from specialized skin poison glands play a central role in defense against predators. The production of toxic secretions is often associated with conspicuous color patterns that warn potential predators Glands keep the skin moist to prevent drying Most amphibians breathe through lungs and their skin. Their skin has to stay wet in order for them to absorb oxygen so they secrete mucous to keep their skin moist and If they get too dry, they cannot breathe and will die). Oxygen absorbed through their skin will enter blood vessels right at the skin surface that will circulate the oxygen to the rest of the body. Sometimes more than a quarter of the oxygen they use is absorbed directly through their skin. T It produces sticky secretions. They also produce sticky secretions that help a male cling to a female during mating and produce toxic chemicals hat discourage potential predators. The skin of amphibians is usually smooth but it may have warts or ridges due to keratin deposit. Most amphibians have thin skin that is very permeable . This is important for two reasons. First, it means that their skin helps them breathe, since oxygen passes easily through it. Second, it means that amphibians lose a lot of water through their skin. The skin of many amphibians is smooth, although epidermal thickenings may produce warts, claws, or sandpapery textures, which are usually the result of keratin deposits or the formation of hard, bony areas. Color change takes place through pigment bearing cells called chromatophores. Chromatophores are specialized cells in the epidermisand dermis of the skin that are responsible for skin color and color changes. Pigmentation is used by many animals for protection, by means of camouflage, mimicry, or warning coloration. Pigments such as melanins in the skin may serve to protect tissues from ultraviolet radiation. Pigments may also aid in sexual reproduction, by identifying species and gender of animals to potential mates, or signaling readiness to breed. Water buoys and supports aquatic animals. Water buoys and supports aquatic animals. The skeletons of fishes function primarily in protecting internal organs, providing points of attachment for muscles, and keeping the body from collapsing during movement. In terrestrial vertebrates,however, the skeleton is modified to provide support against gravity, and it must be strong enough to support the relatively powerful muscles that propel terrestrial vertebrates across land. The amphibian skull is flattened, is relatively smaller, and has fewer bony elements than the skulls of fishes. These changes lighten the skull so it can be supported out of the water. Changes in jaw structure and musculature allow terrestrial vertebrates to crush prey held in the mouth. Support relatively powerful bones that propel teres trial vertebrates across land. The vertebral column of amphibians is modified to provide support and flexibility on land (figure 19.9). It acts somewhat like the arch of a suspension bridge by supporting the weight of the body between anterior and posterior paired appendages. Supportive processes called zygapophyses on each vertebra prevent twisting. Unlike fishes, amphibians have a neck. The first vertebra is a cervical vertebra, which moves against the back of the skull and allows the head to nod vertically. The last trunk vertebra is a sacral vertebra. This vertebra anchors the pelvic girdle to the vertebral column to provide increased support. A ventral plate of bone, called the sternum, is present in the anterior ventral trunk region and supports the forelimbs and protects internal organs. It is reduced or absent in the Anura. Precise control over their long hind legs allows the amphibians to achieve an “amazing” range of jump angles, from near-horizontal to almost vertical. The skeleton of the frog consists chiefly of bony and cartilaginous elements. The functions of a skeleton include providing support for the body, protection of delicate internal organs and attachment surfaces for muscles. The skeletons of salamanders and newts are adapted for a primitive form of walking. The skeleton is relatively unossified with a long vertebral column. The forelimbs and hind limbs are the same size and the humerus and femur are held horizontally to the body. Tetrapods depend more on appendages than on the body wall for locomotion. Thus, body-wall musculature is reduced, and appendicular musculature predominates. Salamanders employ a relatively unspecialized form of locomotion that is reminiscent of the undulatory waves that pass along the body of a fish. Terrestrial salamanders also move by a pattern of limb and body movements in which the alternate movement of appendages results from muscle contractions that throw the body into a curve to advance the stride of a limb (figure 19.10). Caecilians have an accordion- like movement in which adjacent body parts push or pull forward at the same time. The long hindlimbs and the pelvic girdle of anurans are modified for jumping. The dorsal bone of the pelvis (the ilium) extends anteriorly and securely attaches to the vertebral column, and the urostyle extends posteriorly and attaches to the pelvis These skeletal modifications stiffen the posterior half of the anuran. Long hindlimbs and powerful muscles form an efficient lever system for jumping. Elastic connective tissues and muscles attach the pectoral girdle to the skull and vertebral column and function as shock absorbers for landing on the forelimbs. Adult amphibians are carnivores that feed on a wide variety of invertebrates. The diets of some anurans, however, are more diverse. The main factors that determine what amphibians will eat are prey size and availability. Most larvae are herbivorous and feed on algae and other plant matter. Most amphibians locate their prey by sight and simply wait for prey to pass by. Olfaction plays an important role in prey detection by aquatic salamanders and caecilians. Many salamanders are relatively unspecialized in their feeding methods, using only their jaws to capture prey. Anurans and plethodontid salamanders, however, use their tongues and jaws to capture prey. The prey capture mechanism differs somewhat in the two groups. A true tongue is first seen in amphibians. The anuran tongue attaches at the anterior margin of the jaw and folds back over the floor of the mouth. Mucous and buccal glands on the tip of the tongue exude sticky secretions. When prey comes within range, an anuran lunges forward and flicks out its tongue.
