Amphibia refers to "double life", or life in water and on land

Includes the salamanders, frogs, toads, and caecilians with approximately 3,900 spp.

Characterized by:

• Being tetrapods (4 limbs) that facilitate moving about on land - these limbs evolved from the pectoral and pelvic fins
• Skin is thin, soft, glandular and magid (lack scales except in the caecilians) - skin of caecilians with scales similar to those of fish
• Ectothermic
• Both gill and lung breathers - usually gills in the larval stage, replaced by lungs in the adult; cutaneous respiration in many
• Three-chambered heart with two atria and one ventricle

• fertilization may be internal or external
• egg-layers (oviparous) but may have modifications associated with development
• egg anamniotic - doesn’t have a shell but covered with a series of gelatinous layers
• hatchling in aquatic larval form which breath by gills
• most larvae herbivorous, some omnivorous to carnivorous
• larval stage may last from 10 days to 20+ years

• unable to regulate body temperature
• skin types limit distribution to warm, moist climates (i.e. tropics, subtropics, and temperate zones)
• most US species in the south; not found in dry areas
• generally limited to freshwater lakes, streams, ponds - none are true marine forms

• Subclass Labrinthodontia - looked like a salamander
• represented by genus Ichthyostega (fish with feet or legs)
• identified by specific labronthodont tooth
• Subclass Lepospondyli
• named for vertebral type with three fused parts
• Subclass Lissamphibia - contains all living specimens
• where living amphibians evolved is not clear - modern (living) amphibians appeared in Triassic

• Caudata (Urodela) - Salamanders
• Anura (Salientia) - Frogs and toads
• Apoda (Gymnophiona) - Caecilians

• "bearing a tail"
• ~340 species worldwide, 9 Nearctic families, 6 in US - most holarctic (N. hemisphere)
• have four limbs usually of equal size, a tail, and elongated body
• skin is smooth and glandular with mucus and poison glands
• found primarily under leaf litter, in soils, or may be fully aquatic
• most have internal fertilization by way of a spematophore (packet of sperm deposited by the male which is picked up by the female following courtship; gelatinous coating dissolves to release sperm
• all predaceous - none herbivorous: feed on insects, worms, etc.

• come out of burrows, mate, and return to burrows
• eggs develop in ponds
• increased rainfall seems to stimulate breeding
• most species breed annually although some breen only every two years

• cloacal glands enlarge during reproductive activity to contribute mucus layers to spermatophore
• male skin slightly rougher and caudal fins become longer
• hedonic glands in male

Egg and larval development may follow one of five general pathways

• Both egg and larval stages aquatic
• Necturidae, Amphiumidae, most Ambystomatidae permanently aquatic
• Eggs terrestrial, larvae aquatic
• Ambystoma opacum (marbled salamander) lay eggs in depressions which fill with rainfall; eggs hatch as aquatic larvae
• eggs terrestrial, larvae terrestrial
• Plethodontid Desmognathus aeneus - larval form does not feed before developing into adult
• eggs terrestrial with direct development
• Plethodontids which develop from egg directly through larval stage to adult
• eggs retained in the oviduct and fully develop, followed by live birth

• in open static water (lentic systems) - sirens and salamandrids
• in running water (lotic systems) - some plethodontids
• eggs deposited under rocks, debris
• terrestrial sites - Plethodontids
• deposited away from water under logs, rocks, leaf litter
• eggs of salamanders typical for amphibians
• mesolecithal (~50% yolk) surrounded by vitelline membrane and gelatinous capsule
• sperm typically have acrosome, headpiece, and tail
• acrosome contains some golgi and important for fertilization
• headpiece contains the nuclear material
• tail consists of flagella for locomotion and mitochondria in midpiece
• sperm delivered by spermatophore - stalk supporting sperm cap 2-10mm above substrate
• stalk secreted by cloacal glands; sperm cap by pelvic glands

• "hidden gill"
• contain the largest living salamanders
• distributed in eastern US, Japan, one species in China to 9’
• Cryptobranchis alleganiensis found in Appalachians of Kentucky/Tennessee

• restricted to US and Canada
• represented by marbled, tiger, and small-mouthed salamanders

• only three species in the world
• named for the number of toes
• Amphiuma tridactylum in Walker County

• breath entirely through the skin and floor of the mouth
• many New World species which may breed on land

• represented by five species in the US all in the genus Necturus
• permanently aquatic salamanders which retain functional gills as adults

• US and European distribution
• rough-skinned with no costal grooves

• 3 species restricted to the eastern US - lesser, greater, and dwarf sirens
• Siren intermedia (lesser siren) in Walker Co.)
• permanently aquatic with front legs and no back legs, external gills

• ~3,400 species
• have 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
• more widespread than the salamanders
• vocalizations are restricted primarily to the male for courtship, establishing territories - may be resonated by a vocal pouch
• most have external fertilization where eggs and sperm are shed directly into the water - general reproduction patterns follow that of salamanders

Two primary reproductive positions:
Axillary - male grasps the female just behind the forelimbs
Inguinal - male grasps the female around the waist just in front of the hind limbs
remain in position until eggs and sperm are released for fertilization

Family Ascaphidae - tailed frog

• represented only by Ascaphus truei in mountainous Pacific NW
• male retains its tail as an intromittent organ as an adaptation for mating in fast-flowing streams - copulation may last for 24-30 hours, sperm viable for up to 2 years

• eye with an elliptical pupil; expanded horny digger on hind feet
• primarily live underground and come out at night
• breed in temporary pools and young may develop from egg and larval stage in 12 days

• SW US and Rio Grande River valley
• most species tropical laying eggs on land
• frog-like in appearance with prominent tubercles on underside of toes near joints

• ~350 species worldwide - all 17 US species in the genus Bufo
• skins very warty with partid glands behind the eyes - secretes bad tasting poisonous substance as a protection against predators
• shorter legs designed for hopping rather than leaping
• typically burrow at night

• ~700 species worldwide; Acris, Hyla, and Pseudacris in Walker Co.
• Hyla are the true tree frogs with large adhesive toe pads and very little webbing between the toes - arboreal
• Pseudacris mostly ground dwellers with almost webless toes and very small or no toe pads

• small to large frogs with long legs and slim waist
• large, distinct eardrum
• broadly webbed hind feet and usually with a prominent ridge down each side of the back
• aquatic to terrestrial with aquatic larvae
• represented by the genus Rana

• small, chunky anurans with a smooth skin, a small head with a pointed snout, and short limbs
• arboreal, terrestrial, or burrowing
• terrestrial larvae may be nonfeeding

• a general reduction in skull and girdle elements
• pelvic girdle attackes to a single sacral vertebra
• single cervical vertebra (atlas) articulates with two occipital condyles - no second differentiated axis
• no differentiation in the thoracic and lumbar vertebrae anterior to the urostyle followed by a single sacral vertebra
• ribs if present never articulate with the sternum
• distal limb bones fused - tibiofibula and radio-ulna
• increased joints in pelvic limbs to increase jumping ability

• name means “without legs” - a worm-like animal
• subterranean diggers
• ~160 species restricted to tropics and subtropics
• eyes may be covered by skin or even bone
• tentacle of head may serve as a chemosensory organ to detect underground prey
• vivipary common - young 30-60% of female’s body size when born
• initial growth of fetus supported by yolk sac, embryos feed on uterine milk secreted from the epithelial wall of oviduct

• earliest amphibians probably covered with scales - still apparent in some cacaelians
• epidermal layers highly glandular although glands actually located in dermis
• mucus secretions for reduction of water loss
• venom glands - poisonous or toxic substances
• hedonic glands - male head or chin - pheromonally stimulates female to clasp and reproduce
• cornified layers shed in pieces
• males usually lacking claws, some with cornified extensions similar in appearance
• colors variable, produced by lipophores (lipid-soluble, yellow-red), melanophores (melanin, tawny-black), guanophores (guanine crystals, clear-white), ameboid (change shape and location to produce color variation)