Difference between Urodela, Anura and Apoda

Amphibians are vertebrate tetrapods that include salamanders, frogs, toads and caecilians. The word amphibian, that is a Greek word, translates to dual life referring to their ability to survive both in terrestrial and aquatic environments. There are three extant orders under the class Amphibia namely, Urodela (salamanders), Anura (frogs and toads) and Apoda (caecilians). This article focuses on differentiating between the three orders.

Urodela

The order Urodela, also known as Caudata comprises the tailed amphibians, salamanders and newts. They have the least specialised bodies out of all amphibians and appear lizard-like. They have an elongated, slender and stout body with well developed musculature and a tail. The classification of the Urodela order is as follows:

Kingdom: Animalia

Phylum: Chordata

Class: Amphibia

Order: Urodela

The salamanders are a diverse group of organisms. Around 620 species of salamanders are known. They can survive in terrestrial, aquatic, arboreal, and burrowing environments. They prefer living in moist places on land but have to return to water for breeding. However, some species are totally aquatic in nature. The terrestrial salamanders may reach up to 1 m in length and have tails as long as the body. The aquatic salamanders are larger and may grow up to 1.8 m long.

They can respire through gills, lungs, skin and oral cavity. They develop gills at the larval stage which can either remain through their entire life or can be shed after metamorphosis. Lungs in adult salamanders are not as complex as mammals, they are simple and sac-like. They have four limbs in two pairs, the most developed among all amphibians. They lack middle ear cavities but can sense airborne vibrations.

Salamanders are predators that feed other amphibians, insects, fishes and small mammals. They possess teeth in both upper and lower jaws and even the larvae possess teeth. The terrestrial salamanders have a long tongue that is sticky in nature. They flick out their tongue to prey, and the whole event takes less than half a second.

The salamanders have a soft body with slimy skin. This acts as a line of defence to escape the predators. Secondly, they have organs on their tail that secrete poisonous substances to keep the predators away. Their fertilisation is mostly internal.

Anura

The order Anura of the class Amphibia comprises frogs and toads. They are the most diverse group of amphibians with more than 4500 species known. The frogs and toads of the order Anura have short, tailless bodies, big mouths and flat heads with long, muscular hindlimbs. The taxonomic classification is as follows:

Kingdom: Animalia

Phylum: Chordata

Class: Amphibia

Order: Anura

Their body structures have evolved to help them in jumping. Animals with long hind limbs and smooth, slimy bodies are referred to as frogs. On the other hand, animals with shorter limbs and rough skins are referred to as toads.

The frogs are terrestrial, aquatic as well arboreal inhabitants. The muscular hindlimbs strengthen their crouching position that propels the frog high in air. Frogs mostly feed on insects and invertebrates, smaller rodents and other frogs. The frogs lay their eggs in clumps on quiet water surfaces or submerged vegetation. The eggs are fertilised externally. The egg cracks to form a tadpole that is mostly aquatic in nature.

The tadpole then undergoes metamorphosis to form an adult frog. They have a visible tympanic membrane on each side of their head. The frogs save themselves from the predators by their jumping skills. Another mechanism is the presence of parotid glands near the head that produces toxic substances.

Apoda

The class amphibia comprises limbless amphibians classified in the order Apoda, also called Gymnophiona. The limbless amphibians are also referred to as caecilians. The group is known as caecilians because the word caecus in Latin means sightless or blind, which the limbless amphibians are.

The classification of limbless amphibians is as follows:

Kingdom: Animalia

Phylum: Chordata

Class: Amphibia

Order: Gymnophiona / Apoda

They are burrowers that live in moist soils near streams, lakes and ponds. They have cylindrical bodies with annular rings. They completely lack limbs, so that the smaller ones look like worms and the longer ones look like snakes. About 189 species of the group are known that are divided into 35 genera and 10 families.

They are found in tropical regions all over the world. They are mostly viviparous in nature and the fertilisation is internal. These amphibians mainly feed on earthworms and other soft-bodied animals. The caecilians have tentacles that are chemosensory in nature, and help in locating their quarry.

They have sharp teeth arranged in two rows that help in mastication and swallowing. They have bony skulls that help in burrowing. They have specialised skin glands that produce toxins to repel the predators. They are generally not poisonous. The respiration is through lungs, skin, or oral cavity. The locomotion takes place by musculature and hydrostatic motion. They also possess dermal scales. Their hearts are three-chambered.

Their eyes are covered by skin in most of them; they lack middle and outer ear cavities but can detect low-frequency sounds. The caecilians lack functional bone marrow, and hence are dependent on liver, kidney and spleen for blood cell production.

Urodela vs. Anura vs. Apoda

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Also Read:

• Difference Between Frog And Toad
• Important Difference Between Amphibians and Reptiles
• Differences Between Invertebrates And Vertebrates