lungless salamander

▪ amphibian

  any of more than 370 species of lungless amphibians dependent largely on cutaneous respiration (gas exchange through moistened skin). Plethodontidae is the largest group of salamanders (salamander), and its members occur predominantly in the Americas from southern Canada to the Amazon basin in Brazil. A few species also occur spottily in Sardinia, northern Italy, and the Korean peninsula. Adult plethodontids range in size from approximately 25 mm (1 inch) in head and body length in the Mexican pygmy salamander (Thorius) to 36 cm (14 inches) in Bell's false brook salamander (Pseudoeurycea bellii). The length of the animal's tail usually equals or slightly exceeds its head and body length. Most plethodontid species are between 40 and 120 mm (1.6 and 4.7 inches) in head and body length. Since they lack lungs, all plethodontids breathe through their skin and the mucous membrane in the mouth and throat; these surfaces must remain moist at all times in order to absorb oxygen.

      All lungless salamanders possess a pair of nasolabial grooves, and each groove extends from the upper lip to a nostril. The salamander touches its snout to a surface (nose tapping), and capillary action (capillarity) moves odour particles up the groove into the sensory cells in the vomeronasal organ (Jacobson's organ) of the nose. Plethodontids rely on odours for chemical alarm cues, directions to food sources, and cues for courtship and other social behaviour. Smaller species eat a wide variety of small invertebrates (invertebrate) that range from worms (worm) to insects (insect) and mites (mite). Larger plethodontids also consume invertebrates, and some of them even prey on other salamanders.

      Plethodontid lifestyles vary widely and range from fully aquatic to entirely terrestrial. Some terrestrial forms are semiburrowing, whereas others are arboreal (tree dwelling). About 35 species—spanning the genera Eurycea, Gyrinophilus, Pseudotriton, and Stereochilus—lay aquatic eggs (egg) that hatch into free-swimming larvae (larva), which eventually metamorphose (metamorphosis) into adultlike juveniles. Other species are characterized by embryos (embryo) that complete their development within the egg capsule and hatch directly as adultlike juveniles.

      Family Plethodontidae is divided phylogenetically into the subfamilies Desmognathinae and Plethodontinae. The desmognathines are made up of two genera (Desmognathus and Phaeognathus) and 18 species strictly limited to eastern North America. Desmognathine salamanders range from fully terrestrial forms, such as the Red Hills salamander (P. hubrichti), to aquatic forms, such as the black-bellied salamander (D. quadramaculatus). All desmognathine species lay eggs, and females guard the eggs regardless of whether the eggs hatch into larvae or into adultlike juveniles.

      The plethodontines are made up of more than 25 genera and 250 species that occur throughout the range of the family. All are egg layers, and the majority of species in this group have eggs that develop directly into adultlike forms; however, some aquatic species have free-living larvae. Most other plethodontines are forest species, and over four dozen of these belong to Plethodon, the most diverse North American genus. The majority of species in this genus live on the floors of forests and woodlands that have been fragmented by human activity. Bolitoglossa and Pseudoeurycea, two genera found in mountainous areas in the New World tropics, possess their greatest diversity in middle-elevation cloud forests (cloud forest); some of these species are arboreal and live in epiphytes (epiphyte). Web-toed salamanders, plethodontines of the genus Hydromantes, prefer nonforested areas; they mainly inhabit rock crevices in desertlike environments in Europe, California, and Baja California. The embryos of all terrestrial and arboreal plethodontines undergo direct development and hatch into adultlike forms. Females of most species guard their eggs.

George R. Zug

 

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