Introduction & Physical Description
Cryptobranchus alleganiensis is the largest salamander in North America, and the third largest in the world, reaching up to 30 inches from snout to tail tip, and weighing around 4-5 pounds (Humphries). The body is dark brown, greenish, or gray with some black mottling about the back, head, and tail. Reddish or orangish individuals are also found. The limbs are short and thick, with cornified tips on the digits that help grip the substrate in fast flowing waters. There are five toes on the hind feet and four on the front feet. The head and body are flattened, and the tail is laterally compressed and paddle-like in shape. There are large folds of skin along the sides of the abdomen that aid in oxygen absorption by increasing the surface area, which is the primary source of respiration, although Hellbenders also possess lungs. Cryptobranchids possess tiny, lidless eyes that serve limited purposes in their habitat. Males and females are roughly the same size. 

Adults produce a sticky mucous when disturbed that is noxious to some predators. The mucous layer serves to protect against infection, predation, and probably reduces friction in fast flowing waters.        

Larvae are stream type, with streamlined bodies, short gills, and low tail fins. Hatchlings measure up to 1.3 inches, and advanced larvae max out at 5.12 inches total length (Petranka, 1998). Hatchlings are initially a uniform gray or brown, and are equipped with conspicuous yolk sacs that provide nourishment for the first few months of life. The ventral color changes to white within a few months, and dark blotches and spotting occur about the dorsum and venter with age (Petranka, 1998). The larval stage lasts between 1 and 2 years, at which point partial metamorphosis occurs. Adults are paedomorphic, and retain gill slits into adulthood.  

Evolution & Classification

Cryptobranchus alleganiensis is comprised of two paraphyletic subspecies that differ in geological range and color pattern, C. a. alleganiensis, and C. a. bishopi. The latter differs from the nominate form in having larger blotches about the dorsum and chin, however, location is a more definitive method of determining subspecies (Petranka, 1998). See the Distribution & Habitat section below for more information on subspecies.

Cryptobranchids are characterized by the absence of lacrimals and septomaxillae, and a curved row of palatal teeth set parallel to the maxillary and premaxillary teeth (Duellmann & Trueb, 1986). Cryptobrancihds are also external fertilizers, a characteristic not unique to the family Cryptobranchidae.

Cryptobranchidae and the Asian family Hynobiidae comprise the suborder Cryptobranchoidea, the ancient or primitive salamanders. Characteristics of the suborder Cryptobranchoidea include short dorsal processes of the premaxillae that do not separate the nasals, nasals that are ossified from two analagen, an angular that is not fused with the prearticular, the presence of ypsiloid cartilage and the second ceratobranchials, amphicoelous vertebrae where only the posterior caudal vertebrae exist intravertebrally, unicapitate ribs, and external fertilization (Duellman & Trueb, 1986). Unique to Cryptobranchoidea is the fusion of the first hypobranchial and the first ceratobranchial into a rod, and the fusion of the m. pubotibialis and m. puboischiotibialis (Duellman & Trueb, 1986).

Fossil Cryptobranchids are known from the Paleocene, Miocene, and Pleistocene in North America, the Oligocene through the Pliocene in Europe, and the Pleistocene in Asia (Duellman & Trueb, 1986). Cryptobranchids are thought to be derived from a hynobiid-like ancestor through the retention of larval characteristics into adulthood (Duellman & Trueb, 1986). Fossil species were even larger than the extant species, exceeding 6.5 feet (2 meters). Cryptobranchids are thought to have evolved from Hynobiid-like ancestors, and today Cryptobranchid larvae are morphologically similar to Hynobiid larvae. 

Synonymy & Etymology

Vernacular Synonymy: Hellbender, Allegany Hellbender, Groundpuppy, Ground-puppy, Tweeg, Menopome, Mud Devil, Tennessee Hellbender, Brown Hellbender, Giant Salamander, Alleghany Salamander, Eastern Hellbender, Ozark Hellbender, Mudpuppy, Mollyhugger, Mud Cat, Snot-Otter, Grampus

Etymology: The genus name Cryptobranchus is Greek and translates to "hidden gills"; kryptos = hidden, and branchion = gill (Beltz, 2004). This refers to the lack of external gills characteristic of other paedomorphic and larval salamanders. The species alleganiensis is in refers to its habitat in the Allegheny Mountains of Virginia. 

Distribution & Habitat

C. alleganienis inhabit cold, fast moving rivers and streams, where they generally hide under rocks and logs during the day and emerge to forage at night. Adults are found mainly in shallower waters of 1-3 feet, but the complete ecology of larvae are unknown, and it has been suggested that larvae may enter deeper waters more frequently. C. alleganiensis are light sensitive, capable of physically detecting light shone on the skin, and live primarily nocturnal lives. Some may come out of hiding during overcast days. Individuals occupy a particular territory, the size of which varies among populations, and have homing abilities both upstream and downstream (Petranka, 1998). Homes, consisting of concealed areas under rocks and logs, are defended from intruding conspecifics.

Breeding Behavior

Before mating, males choose and create the nest site, which is typically an excavated depression covered by rocks, logs, or other cover, with the entrance positioned such that the water current does not flow directly into the nest site. Males wait for gravid females in the nest site, with their heads protruding from the entrance. Females seek out occupied nest site, and are guided in by the awaiting males. Males may aggressively prevent females from leaving the nest site until they have produced eggs (Petranka, 1998).

While in the nest, males basically show no interest in the females until they begin producing eggs. Fertilization is external, and during oviposition, the male positions himself above or beside the female and sprays the eggs with seminal fluids. Females produce several hundred eggs in rosary-like strings, over a 2-3 day period, and C. a. bishopi produce more ova than equal size C. a. alleganiensis (Petranka, 1998). Clutch size is positively correlated with the total length and age of the female. The parents will cannibalize a good portion of the eggs in each clutch. Fresh ova are 5-7 mm in diameter, around 18-20 mm including the envelopes, and are white or yellowish in color (Petranka, 1998). Eggs may swell to 20-30 mm just before hatching (Petranka, 1998).

Nests are usually solitary, but communal nests housing several thousand eggs have been observed (Bishop, 1941).

After oviposition, the female is chased away by the male, who remains in the nest to brood the clutch. Males increase the oxygen supply in the nest by rocking back and forth, and undulating the flaps of skin on the abdomen and limbs (Bishop, 1941). Brooding males aggressively defend their nests against egg robbing conspecifics, as well as potential predators of other species. 

Eggs hatch approximately 45-75 days after oviposition, depending on the exact location. At one year old, larvae may measure 60-70 mm (Bishop, 1941). At about one year old, individuals will grow 60-70 mm per year, until partial metamorphosis. At 1.5-2.0 years of age, and at around 100-130 mm, partial metamorphosis commences, and larvae lose their external gills, retaining open gill slits (Duellman & Trueb, 1986; Petranka, 1998).

After partial metamorphosis, growth rates steadily decline to approximately 1 mm per year in very old individuals (Petranka, 1998). Sexual maturity is reached at around 5-8 years and between 30-39 cm total length, and males mature at a smaller size and younger age than females (Petranka, 1998). C. alleganiensis are thought to live 25-30 years in the wild (Nigrelli, 1954).

Threats & Conservation Status

Hellbenders require a clear stream with large rocks for breeding. Siltation of streams and rivers is devastating to Hellbenders because it covers up the vital rocky composition of their habitat. Siltation also negatively affects crayfish populations, which together with fish comprise 90% of the Hellbenders diet, for the same reasons (Petranka, 1998). Siltation can occur from badly built roads, overabundance of roads, poor forestry practices, and from erosion resulting from farming and building development (Humphries).

Damming essentially converts fast flowing rivers into still lakes, drastically altering the river habitat required for Hellbender survival. Hellbenders inhabit fast flowing waters, for which they are physiologically adapted for. A decrease in water flow results in a decrease in dissolved oxygen content, and also causes the temperature of the water to rise, both of which are detrimental to Hellbenders. 

Because of their slow development and high mortality rate, taking too many Hellbenders from the wild can have a dramatic effect on wild populations. In the past, and to some degree today, Hellbenders were taken from the wild for pets. Because of their huge size and particular habitat, Hellbenders usually die in captivity, and at the least, do not reproduce. Hellbenders are also sometimes injured or killed by accident or neglect by fishermen who snag them on their lines.

The status of C. alleganienis changes often. In the past, C. alleganiensis have been listed as endangered, threatened, and species of special concern (Nickerson & Krysko, 2003). Currently, C. alleganiensis is listed as Near Threatened with the IUCN (Red List). The Ozark subspecies, C. a. bishopi is a candidate for listing under the U.S. Endangered Species Act (NatureServe, 2004). Many populations are also protected under state law. For a detailed summary of state listings, see Jeff Humphrie's Hellbender Homepage, Conservation section.

The Hellbender Homepage
The Andrias Homepage
Tree of Life web project: Cryptobranchida
Georgia Wildlife: Cryptobranchida
AmphibiaWeb: Cryptobranchidae
Crayfish Predators in North America