Necturus

The genus Necturus is under scrutiny by herpetologists.[2] The relationship between the species is still being studied. In 1991 Collins reelevated N. maculosus louisianensis to full species status as N. louisianensis. Originally described by Viosca as a species, it usually had been considered a subspecies of the common mudpuppy (N. maculosus). However, the interpretation of Collins was not largely followed.[2][6][7] Then, a 2018 study confirmed it as a distinct species, with Amphibian Species of the World following these results, although other authorities do not.[8][9][10]

There are seven to eight species:[6]

Image	Scientific name	Common Name	Distribution
	Necturus alabamensis Viosca, 1937	Alabama waterdog	Alabama.
	Necturus beyeri Viosca, 1937 synonym: N. lodingi Viosca, 1937	western waterdog (formerly the Gulf Coast waterdog) or Mobile mudpuppy. These two names have been recognised as independent species in the past.[3][11]	Alabama, Louisiana, Mississippi, and Texas.
	Necturus lewisi Brimley, 1924	Neuse River waterdog	North Carolina.
	Necturus louisianensis Viosca, 1938	Red River waterdog. Sometimes considered a subspecies of N. maculosus.[8][10]	southeastern Kansas, southern Missouri, northeastern Oklahoma, Arkansas, and northcentral Louisiana.
	Necturus maculosus (Rafinesque, 1818)	common mudpuppy	southern section of Canada, as far south as Georgia
	Necturus moleri Guyer et al., 2020	Apalachicola waterdog	southeastern Alabama, the Panhandle of Florida, and southwestern to north-central Georgia.
	Necturus mounti Guyer et al., 2020	Escambia waterdog	southern Alabama and the Panhandle of Florida.
	Necturus punctatus (Gibbes, 1850)	dwarf waterdog	from southeastern Virginia to southcentral Georgia.

Nota bene: A binomial authority in parentheses indicates that the species was originally described in a genus other than Necturus.

Two known fossil species, N. krausei and an unnamed species, are respectively known from the Paleocene of Saskatchewan and from Florida during the Pleistocene.[12][13]

Necturus are paedomorphic: adults retain larval-like morphology with external gills, two pairs of gill slits, and no eyelids. They are moderately robust and have two pairs of short but well-developed limbs and a large, laterally compressed tail. Lungs are present but small. Typical adult size is 20–25 cm (8–10 in) in total length, but Necturus maculosus is larger and may reach 40 cm (16 in).[4]

N. maculosus is brown to gray on its back with bluish black spots. There may be spots on its belly, but these spots range from heavily spotted to no spotting. There are dark red bushy gills. Four toes are present per hindlimb.[14]

Females lay eggs under rocks and other large cover objects in late spring and early summer.[15] Females guard nests at least until eggs hatch.[5] Females forage while nest-guarding, but they may eat some of their eggs as a source of energy if other food sources are not readily available.[5] Larvae are believed to stay under the rock as late as November.[5]

Necturus occur in surface waters, preferentially with clear water and rocky substrates without silt. N. maculosus live in lakes, rivers, streams, and creeks.[15][16] They like shallow waters with low temperatures from autumn to early spring.[15] They are most active in cold temperatures, specifically between 9.1 and 20.2 degrees Celsius.[16][17] During the day, N. maculosus seeks refuge under rocks or logs and plant debris.[15] They forage during the night and eat a variety of prey, but have preference for crayfish.[4] During the winter and spring, N. maculosus will also eat fish.[5]

N. maculosus are good indicators of ecosystem health.[16] This species has frequently been harmed via bycatch events (primarily passive ice fishing), chemical pollutants, and siltation.[16] Amphibian chytrid fungus (Bd) has been known to affect captive N. maculosus, but it is currently unknown whether it has affected wild N. maculosus.[17]

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