Amphibians

Modern Amphibians Skeleton mostly bony Body forms vary greatly varying numbers of vertebrae; ribs present in some, absent or fused to vertebrae in others Body forms vary greatly elongated trunk with distinct head, neck, and tail to a compact, depressed body Limbs usually four (tetrapod) Some are limbless some have forelimbs much smaller than hindlimbs Some have limbs small and vestigial Webbed feet often present no true nails or claws forelimb usually with four digits but sometimes five and sometimes fewer

Modern Amphibians Skin usually smooth and moist with many glands some of which may be poison glands pigment cells (chromatophores) common, or considerable variety no scales - except concealed dermal ones in some Mouth usually large with small teeth in upper or both jaws two nostrils open into anterior part of mouth cavity Respiration by lungs (absent in some salamanders), skin, and gills in some either separately or on combination external gills in the larval form and may persist throughout life in some

Modern Amphibians Heart Ectotherms Excretory system sinus venous, two atria one ventricle, a conus arteriosus, double circulation through the heart skin abundantly supplied with blood vessels Ectotherms Excretory system paired mesonephric or opisthonephric kidneys urea main nitrogenous waste Ten pairs of cranial nerves

Modern Amphibians Many amphibian species make use of both aquatic and terrestrial habitats either simultaneously or sequentially during different life stages. A typical life cycle involves semiterrestrial adults that breed and lay eggs in water. Eggs then develop into aquatic larvae. the larvae undergo metamorphosis, or transformation, and become semiterrestrial adults. Metamorphosis is triggered by changes in concentrations of circulating hormones metamorphosis is most extreme among frogs, where there is a striking difference between the larva (the tadpole) and the adult.

Modern Amphibians All amphibians are carnivorous, exception of larval frogs (tad-poles), which are primarily herbivorous. Most amphibians are generalists, and will eat anything they can capture and ingest. Frogs and salamanders capture prey with their tongues, which are highly developed. Certain salamander species have specialized projectile tongues that they fire with impressive accuracy to capture prey.

Modern Amphibians Three living amphibian orders comprise more than 5400 species Order Gymnophiona (Apoda) caecilians Order Urodela (Caudata) Salamanders Order Anura (Salientia) Frogs & toads

Order Gymnophiona 160 species Elongate, limbless, burrowing creatures Found in tropical forests of South America, Africa, Southeast Asia Long, slender body, small scales Diet consists of worms & small invertebrates Internal fertilization; eggs deposited in moist ground near water

Caecilians – legless amphibians

Order Urodela Tailed amphibians Oura – tail; delos – evident Tailed amphibians ~500 species of salamanders Found in almost all northern temperate regions Most abundant & divers in North America Also found in tropical areas of Central America & South America Most are less than 15 cm long Japanese giant salamander exceeds 1.5 m

Order Urodela Breeding behavior Internal fertilization Female recovers in her vent a packet of sperm (spermatophore) Deposited by a male on a leaf or stick Aquatic lay eggs in water Terrestrial lay eggs in soft moist earth

Order Anura Frogs & Toads – more than 4840 species An – without; orua - tail Frogs & Toads – more than 4840 species Occupy a variety of habitats Aquatic mode of reproduction & water-permeable skin prevents them from wandering too far from water Ectotherms four limbs usually of unequal size hind limbs are elongated and modified for jumping head and trunk fused, tail in larval form lost as adult vocalizations are restricted primarily to the male for courtship, establishing territories most have external fertilization where eggs and sperm are shed directly into the water Generalized reproductive pattern males vocalize to attract females adults predaceous - insectivorous/carnivorous

Order Anura Habitats & Distribution Temperate & tropical regions Except New Zealand Oceanic islands & southern South America Live near water Some in damp forest Patchy in distribution Restricted to certain localities (specific stream or pool)

Order Anura Reproduction External fertilization Eggs begin to develop immediately Tadpoles develop within a few days