An aquatic, cave-dwelling salamander. This weird-looking animal is gilled throughout life, has extremely thin limbs, and is virtually pigmentless. The eyes are reduced and non-functional. A tail fin is present. Adults are 9-13.5 cm total length, with 12 costal grooves. Juveniles have proportionally larger eyes. See Petranka (1998) for references.
 
Until recently E. rathbuni and E. robusta were placed in the genus Typhlomolge. Although they are extreme in their specializations for living in underground aquatic systems, these two species are closely related to other species of Eurycea from Texas and the eastern United States (Chippindale 1995; Petranka 1998).

This species can be found in San Marcos Pool of the Edwards Aquifer, Hays County, south-central Texas, USA (Chippindale et al. 2000). They are unlikely to range beyond this region.

The Texas Cave Salamander is limited to the San Marcos, Texas area.

Biogeographic Regions: nearctic (Native )

endemic to a single state or province

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (<100-250 square km (less than about 40-100 square miles)) San Marcos Pool of the Edwards Aquifer, Hays County, south-central Texas (Chippindale et al. 2000).

This species has an extremely restricted range and has been found at a small number of localities near San Marcos, Hays Co. Texas. Adults and larvae are adapted for dwelling underground and may occur quite deep. Pools where this species has been collected have minimal current and nearly constant temperature of 21-22º. See Petranka (1998) for references.

Historic Range:
U.S.A. (TX)

Eurycea rathbuni is characterized by a very broad, flat head and snout. The four limbs are very thin and elongate. The tail is laterally compressed and finned, tapering at its end. The eyes are vestigial and lie beneath the animal's skin. External gills are bright red and always present. The forelimbs have four digits while the hind limbs have five. Eurycea rathbuni is neotenic and thus bright red gills are present throughout the lifecycle. It has twelve costal grooves as well. Adults range in length from 3.25 to 5.375 inches (University of Texas; Potter and Sweet 1981).

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: sexes alike

Length: 14 cm

Holotype for Eurycea rathbuni
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1896
Locality: San Marcos, Hays, Texas, United States, North America

Paratype for Eurycea rathbuni
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1896
Locality: San Marcos, Hays, Texas, United States, North America

Paratype for Eurycea rathbuni
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1896
Locality: San Marcos, Hays, Texas, United States, North America

Paratype for Eurycea rathbuni
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1896
Locality: San Marcos, Hays, Texas, United States, North America

Paratype for Eurycea rathbuni
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1896
Locality: San Marcos, Hays, Texas, United States, North America

Paratype for Eurycea rathbuni
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1896
Locality: San Marcos, Hays, Texas, United States, North America

Habitat and Ecology

Systems

• Freshwater

Eurycea rathbuni is only found in subterranean water systems in Edwards Plateau in Texas. The Edwards Plateau is characterized by springs and caves and lies at an elevation of 600-750 meters. It has been found in wells but is usually restricted to caves (Duellman 1999).

Habitat Regions: temperate ; freshwater

Other Habitat Features: caves

Comments: Water-filled subterranean caverns. In some sites, known only from individuals washed out of artesian wells.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Little is known about this species feeding habits and methods. It may feed on snails, shrimp, and amphipods (University of Texas).

Comments: Eats various small invertebrates (snails, copepods, amphipods, shrimp).

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 5

Comments: Specimens have been collected from several sites, but the number of distinct occurrences is uncertain.

Unknown

Comments: Total adult population size is unknown.

Bat guano is an important source of nutrients in the subterranean ecosystem inhabited by this species.

Comments: Apparently no distinct annual or daily activity patterns.

Development - Life Cycle: neotenic/paedomorphic; metamorphosis

Average lifespan

Status: captivity: 10.3 years.

Maximum longevity: 10.3 years (captivity)

Little is known about the reproduction of Eurycea rathbuni. The species is known to be acyclic with females maturing and reproducing throughout the year, unresponsive to seasonal cues. This breeding cycle is typical of many cave dwelling species (Lofts 1974). Breeding of this species has been observed in the laboratory. The females assumes an active role in stimulating the male to mate. Her behavior is characterized by rubbing her chin along the male's back. If this fails to stimulate the male then she may scratch at him or fan her tail at him. She may even resort to nipping at his sides if he further ignores her advances. The male will deposit a spermatophore on a rock or substrate and the female will then pick it up with her cloaca (Bechler 1988).

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous

See Bechler (1988) for description of courtship behavior. Gravid females and small juveniles have been found throughout the year.

Year Assessed

Assessor/s

Reviewer/s

Justification

History

• 1996
  Vulnerable
• 1996
  Vulnerable
  (Baillie and Groombridge 1996)
• 1994
  Endangered
  (Groombridge 1994)
• 1990
  Endangered
  (IUCN 1990)
• 1988
  Endangered
  (IUCN Conservation Monitoring Centre 1988)
• 1986
  Endangered
  (IUCN Conservation Monitoring Centre 1986)

Eurycea rathbuni is listed as endangered under the U.S. Endangered Species Act (Duellman 1999). Its extremely limited range makes it a vulnerable species.

US Federal List: endangered

IUCN Red List of Threatened Species: vulnerable

United States

Rounded National Status Rank: N1 - Critically Imperiled

Rounded Global Status Rank: G1 - Critically Imperiled

Reasons: Extremely restricted distribution within a very fragile subterranean ecosystem in Texas; aquifer is threatened by water depletion and potential contamination.

Intrinsic Vulnerability: Highly to moderately vulnerable.

Environmental Specificity: Very narrow. Specialist or community with key requirements scarce.

Current Listing Status Summary

Status: Endangered
Date Listed: 03/11/1967
Lead Region:   Southwest Region (Region 2) 
Where Listed:


Population detail:

Population location: entire
Listing status: E

For most current information and documents related to the conservation status and management of Eurycea rathbuni, see its USFWS Species Profile

Population

Population Trend

Global Long Term Trend: Increase of 10-25% to decline of 30%

Comments: Few data, but likely relatively stable in extent of occurrence; uncertain long-term trend in population size, area of occurrence, and number/condition of occurrences.

Very little is known about the biology of this species. Courtship has been observed in captivity. This species has a tail-straddling walk similar to what has been observed in other plethodontid salamanders. Fertilization is by means of a spermatophore deposited on the substrate by the male and picked up in the cloaca by the female (Belcher 1988). Small juveniles have been found throughout the year and breeding may be aseasonal. One gravid female contained 39 mature ova. Known diet items include blind shrimp, snails, and amphipods (Longley 1978).

Major Threats

Degree of Threat: A : Very threatened throughout its range communities directly exploited or their composition and structure irreversibly threatened by man-made forces, including exotic species

Comments: Sensitive to changes in water quality and thus vulnerable to groundwater pollutants (Matthews and Moseley 1990). Potentially threatened by falling groundwater levels that have resulted from increased pumping to support residential and commercial development in the region. Overcollecting formerly (1960s) may have reduced populations in accessible locations.

This species has a restricted range and is not commonly encountered. Eurycea rathbuni is protected at both local and national levels (Petranka 1998).

Conservation Actions

Management Requirements: Maintenance of water level and quality is the most important management consideration. See recovery plan (USFWS 1996).

Biological Research Needs: Research difficult due to the subterranean habitat and fragility of the species.

Global Protection: Few (1-3) occurrences appropriately protected and managed

Comments: Listed Endangered by USFWS (F.R. 03-01-78). TNC purchased Ezell's Cave, 1967.

Needs: Protect the aquifer from pollution and depletion. Protected by TNC at Ezell's Cave, but would benefit from protection of more abundant populations at other sites.

Eurycea rathbuni does not negatively affect humans.

This salamander is not a resource for humans.

Comments: Formerly included in the genus Typhlomolge (see Mitchell and Reddell 1965; Chippindale et al. 1994, 2000).