ZOOLOGY OF CHORDATES: STUDY GUIDE - Zakharenko M.O. - 2015

CHAPTER 4. SUPERCLASS TETRAPODA. LOWER TERRESTRIAL VERTEBRATES

4.2. Characteristics of Selected Amphibian Species.

Amphibians are currently the least numerous Class of modern vertebrates, with approximately 2,500 species grouped into three orders. Ukraine is home to 20 species.

All amphibians are vital components of ecosystems and serve as bioindicators of environmental health. Many species are harvested commercially. Frogs are widely used in laboratories worldwide; in gratitude, researchers have erected monuments to them in Paris and Tokyo. Furthermore, frogs were among the first vertebrate astronauts.

Order Anura, seu Ecaudata (Tailess Amphibians).

The order is divided into 5 suborders comprising 10 families.

The suborder Opisthocoela is characterized by opisthocoelous vertebrae (convex anteriorly, concave posteriorly), short Ribs, and a small Tongue. It includes 2 families: discoglossoids (Discoglossidae, 8 species), distributed across Europe and Asia. Four species of fire-bellied toads (Bombina) inhabit shallow, well-warmed Water bodies. They possess Teeth on their upper jaws and a round, unnotched tongue. In our fauna, these are small animals measuring 4-8 cm in length, with relatively short hind limbs. They have at least 8 trunk vertebrae, which are opisthocoelous. Two species of the genus Bombina occur in Ukraine (Fig. 162).

European fire-bellied toad - Bombina bombina.

Fig. 162. Fire-bellied toads: red-bellied (A) and yellow-bellied (B)

Body length up to 5 cm; body flattened and oval; distributed in Central and Eastern Europe. In Ukraine, it is widespread throughout the country, inhabiting lakes, oxbow lakes, and canals. The belly is brightly orange with bluish-black patches. Males possess internal vocal sacs. Their Skin glands secrete phrynolysin, a potent toxic substance.

Yellow-bellied toad - Bombina variegata - inhabits Central, Southern, and Eastern Europe. In the western regions of Ukraine, it is found in Lviv, Ivano-Frankivsk, Chernivtsi, and Zakarpattia oblasts. The upper side of the body is dark, while the lower side of the limbs and abdomen is orange or yellow with dark patches.

Family Pelobatidae (Spadefoot Toads).

A small group of small toads (5-8 cm in length). Three species are found in our country, including the common spadefoot toad - Pelobates fuscus (Fig. 163).

Fig. 163. Common spadefoot toad

Family Ranidae - True Frogs (Fig. 164).

Fig. 164. True frogs

1 - dark-spotted frog; 2 - pool frog; 3 - marsh frog; 4, 5 - moor frog; 6 - common frog; 7 — agile frog

A numerous group uniting over 400 species distributed across almost all continents except Australia, New Zealand, and most of South America. They are particularly abundant in Africa, home to the giant goliath frog (Rana goliaph), which reaches up to 25 cm in length and weighs over 3 kg. The genus Rana encompasses about 200 species. Some species inhabit humid terrestrial habitats and return to water only during the breeding season. One of our largest species, the marsh frog (Rana ridibunda), grows up to 17 cm. The pool frog (Rana esculenta) is smaller, with a length of 10 cm, and is found throughout Ukraine except for the steppe zone. The common frog (Rana temporaria) is distributed across Europe, Western Siberia, and the Far East. The moor frog (R. terrestris) reaches 7.8 cm in length.

It inhabits dry sandy areas of pine forests, steppes, deserts, and the banks of lakes and rivers with dense herbaceous vegetation. The agile frog (Rana dalmatina), which inhabits specific areas of the Carpathians, also belongs to the true frog family. North America's largest amphibian species is the American bullfrog (Rana catesbeiana), reaching 20 cm in length. Marsh frogs and certain other species are used as human food and are even raised on specialized farms.

Family Hylidae - Tree Frogs (Fig. 165).

Fig. 165. Tree frog

Widely distributed in warm regions across all continents, comprising about 400 species of arboreal frogs. Within Ukraine, they inhabit all landscape zones, being particularly common in the forest-steppe, Polissya, and the forested areas of the Carpathians. Individuals feature widened pads—discs—at the tips of their digits, which act as specialized suction cups that enable them to climb trees. They are widespread in Australia and the Americas. In our region, only a single species occurs—the European tree frog, or tree toad Hyla arborea, which reaches a length of 5 cm. Parental care is pronounced in many species of tree frogs.

Family Toads - Bufonidae (Fig. 166).

Fig. 166. Toads

1 - natterjack; 2 - European green; 3 — common

Its representatives are distributed throughout the entire continent, excluding polar regions, with a total of 650 species. Three species of toads live in Ukraine. Externally, individuals are covered with warty skin rich in glands that secrete a toxic

fluid. Teeth are absent, and the limbs are nearly equal in size. The common toad, Bufo bufo, is the largest among anurans, reaching a length of 20 cm. The green toad, Bufo viridis, has a smaller body size (up to 140 mm) and is widespread across Ukraine. It spawns in the form of gelatinous cords up to 3–5 meters in length. A single female can lay up to 6,000 eggs. The natterjack toad, Bufo calamita, inhabits biotopes in the northwestern districts of Volyn Oblast and settlements in certain areas of Polissya. It is found in gardens, forests, fields, and meadows. It is nocturnal. All toads possess large parotoid glands behind the eyes on the DORSAL SIDE OF the HEAD. The secretion of these glands irritates mucous membranes, forcing predators that seize a toad to release it. The cane toad, Bufo marinus, reaches a body length of 25 cm. Its venom is extremely potent; a dog that bites this toad dies rapidly. Local populations use this venom to tip poisoned arrows.

Order Caudata - Urodela, seu Caudata

Includes about 280 currently extant species. The head merges imperceptibly into an elongated trunk, with a tail that is always laterally compressed. The forelimbs and hindlimbs are of nearly equal length; in some species, they are poorly developed, while in sirens the posterior pair is reduced. They crawl or swim by undulating the body and tail in a snake-like manner. Many tailed amphibians have transitioned to an aquatic lifestyle. They possess well-developed cutaneous glands. They are distributed primarily in the Northern Hemisphere and are absent in Australia (Fig. 167).

Fig. 167. Species of tailed amphibians:

1 - smooth newt; 2 - fire salamander; 3 - amphiuma; 4 - siren; 5 - olm;

6 - tiger salamander; 7 - axolotl.

Suborder Ambistomatoidea includes a single family, mole salamanders - Ambystomatidae, comprising 28 species distributed in North and Central America.

The tiger salamander is widely distributed and best known. Like other species, adults inhabit the shores of water bodies, hiding in shelters during the day. They reach a length of 15–23 cm. The aquatic larvae of many mole salamanders—axolotls—are capable of reaching adult size and reproducing sexually without undergoing metamorphosis (neoteny).

Suborder Proteidea includes a single family, olms - Proteidae. This family encompasses two species of neotenic larvae, possibly belonging to some extinct salamanders. One of them is the European olm, Proteus anguinus, which lives in subterranean waters of the Balkan Peninsula. It has an eel-like reddish body 25–30 cm long with small limbs, featuring three digits on the forelimbs and two on the hindlimbs. Three pairs of feathery external gills are located on the sides of the head. The tail is short and laterally compressed. The eyes are small or covered by skin. Fertilization is internal; the female lays up to 80 eggs, but all of them except two in the lower part of the oviducts undergo resorption (lysis). The lysis products are utilized by the two developing larvae. At a length of about 1 cm, the larvae hatch and lead an independent life.

The mudpuppy, Necturus maculosus, primarily inhabits cold lakes in eastern North America. It is active year-round, freezing into the ice at low temperatures, but revives upon thawing.

Suborder Salamandroidea - comprises 3 families.

Family true salamanders - Salamandridae comprises about 40 species. Eyelids are well developed; vertebrae are opisthocoelous; adults possess functional Lungs, external gills are reduced, and gill slits close; fertilization is internal. They are distributed in Europe, Asia, North Africa, and North America. Salamanders have a stout body and a large, unkeeled tail. Their body length is 10–28 cm, and their coloration is black with bright yellow spots. Fire salamander - Salamandra salamandra.

Family lungless salamanders - Plethodontidae, the most numerous in the order, with about 175 species. They are characterized by the reduction of lungs and the loss of the Pulmonary Circulation circuit. Some species live in mountain streams, while others inhabit caves and damp forests. There are 5 species of salamanders in Ukraine. The body shape is lizard-like; larvae respire through external gills. The most widespread is the smooth newt, Triturus vulgaris, found in the Carpathians, forest-steppe, and forest zones, as well as in river valleys of the steppe zone. It reaches 8 cm, occasionally even 11–12 cm. The Carpathian newt, T. montandoni, is distributed in the Carpathians, frequently found at altitudes up to 1000 m above sea level, reaches up to 8 cm, and is an endemic species. The great crested newt, T. cristatus, has a body length of 15–18 cm. The alpine newt, T. alpestris, inhabits mountain water bodies, migrating to damp terrestrial habitats in summer.

Order Apoda - Gymnophiona

This order includes a single family of caecilians - Caeciliidae. Comprising about 60 species, they externally resemble large worms or snakes with a body length of 30–120 cm. They are characterized by an elongated, worm-like body with annular folds, lacking paired limbs and possessing a tail (Fig. 168).

Fig. 168. Apodan amphibians

1 - ringed caecilian; 2 - Ceylon caecilian; 3 - slender caecilian

All caecilians, with the exception of representatives of two South American genera, lead a fossorial lifestyle, burrowing in moist soil and leaf litter. This is a highly specialized group of animals characterized by an elongated, limbless body lacking limb girdles; a ventrally positioned Mouth; vestigial eyes; an absent tympanic membrane; and a rudimentary auditory nerve. Their olfactory Organs are well developed. Fertilization is internal, with the eversible cloaca functioning as a copulatory organ. They feed on insects, earthworms, and other soil invertebrates. The eggs develop out of water, and only the final larval stage is aquatic. They inhabit South America, tropical Africa, and South Asia. A common species is the Ceylon caecilian (Ichthyophis glutinosus), which coils its body around its clutch to keep it moist. Some species are viviparous. Progressive features of caecilians, much like tailed amphibians, include internal fertilization and parental care. The ringed caecilian (Siphonops annulatus) is distributed in northern Brazil, Peru, and Ecuador, reaches lengths up to 40 cm, and inhabits soil along the banks of rivers and lakes. The female lays five eggs in burrows beneath tree stumps.