Description
Like all members of the family Typhlonectidae, the Rio Cauca Caecilian is an aquatic caecilian, and, like all caecilians, are limbless with reduced cranial features. Typhlonectes natans generally ranges in size from 364 - 595 mm in length and 14.1 - 57.3 g in weight but can reach sizes up to 637 mm in length (Tapley and Agosta-Galvis 2010, Flach et al. 2020); the specimen that reached a length up to 637 mm was female and weighed 172.2 g (Tapley and Agosta-Galvis 2010). Their heads are small and their eyes are well-developed and distinct in bony sockets beneath the skin (Fischer in Peters 1880, Prabha et al. 2000, Vitt and Caldwell 2013). They have small, non-protrusible sensory tentacles close to the nostrils, (Fischer in Peters 1880, Wilkinson and Nussbaum 1999, Zug et al. 2001). On the lower jaw, the second row of teeth generally has 12 - 14 teeth (Fischer in Peters 1880). Typhlonectes natans only have primary annuli that are generally indistinct and disappear on the dorsal side, they may have pseudo-secondary annuli (Fischer in Peters 1880, Vitt and Caldwell 2013). Dermal scales are generally absent in grooves (Vitt and Caldwell 2013). The Rio Cauca Caecilian does not have a tail and the body is laterally compressed especially when approaching the posterior end.

Juveniles of the Rio Cauca Caecilian may be 64 mm in length (Kleinteich 2010).

DIAGNOSIS:

Other caecilians generally lack a right lung, but typhlonectids generally have a well-developed right and left lung, with the lung possibly extending to the cloacal region (Wake and Donnelly 2009).

They have numerous distinct features that distinguish them from other members of Typhlonectidae. Those features are four anterior cloacal denticulations (as opposed to 5 or more), a more narrow and curved postorbital bone, a well-developed and elongated vomerine process at the posterior margins with the vomers, basibranchial cartilage that forms the shape of a “V” as opposed to the typical “Y”), and an elongated capitulum (Wilkinson and Nussbaum 1999). Typhlonectes natans superficially resembles Typhlonectes compressicauda, which as of 2024 is the only other known member of the genus. However, T. natans can be distinguished from T. compressicauda by the former having a wider head width than body, relatively wider body, sharp-tipped tooth shape (vs. broadly dilated crowns in T. compressicauda), and having roughly nine cloacal denticulations compared to 10 - 11 in T. compressicauda (Sheehy et al. 2021).

From reduced limbed aquatic salamanders, Siren lacertina and Amphiuma means, Prabha et al. (2000) notes that all have narrow and elongated lungs, but only T. natans has the anterior trachea connect the buccal cavity to the tracheal lung and the posterior trachea connect the tracheal lung to the left and right posterior lungs (S. lacertina and A. means have the trachea connect the buccal cavity to the tracheal lungs). The trachea is a respiratory structure in S. lacertina and A. means. Conversely, in T. natans the trachea is an air channel to the tracheal lung. Furthermore, all three species have right lungs, but in T. natans and A. means the right lung is generally longer than the left (Prabha et al. 2000).

COLORATION:

Presumed in life, Typhlonectes natans is a uniform brown gray color. They can be a little lighter ventrally (Fischer in Peters 1880).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Colombia, Venezuela. Introduced: United States.

U.S. state distribution from AmphibiaWeb's database: Florida

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (5 records).

Typhlonectes natans is distributed across western and northern Columbia and northeastern Venezuela, at a likely elevation range of 100 - 1000 m (Tapley and Agosta-Galvis 2010, IUCN 2020). They are mostly associated with the drainage basins of the Magdalena and Cauca Rivers in Colombia and the Lake Maracaibo Basin in Venezuela, but Tapley and Acosta-Galvis (2010) believe they can also be found further south to the headwaters of the Urrá River. They are associated with warm, lotic systems during the wet season and then migrate to marshes and lakes before the beginning of the dry season when stream flow is low. Typhlonectes natans can be found during the day taking refuge in the dense root of floating vegetation (Tapley and Acosta-Galvis 2010).

In 2021, Sheehy et al., reported the first occurrence of a caecilian in the United States of America. An individual T. natans found in a canal in Miami-Dade County, Florida in 2019 (Sheehy et al. 2021).

Life History, Abundance, Activity, and Special Behaviors
Highly aquatic, T. natans is known to migrate over the floodplains of the Cauca and Magdalena rivers, moving upstream during the wet season. In the dry season, when flooded river basins shrink to shallow pools, they can be found in deeper streams (Parkinson 2004, Tapley and Acosta-Galvis 2010). Tapley and Agosta-Galvis (2010) state that they are exclusively found in flowing waters, sometimes wrapped within the dense roots of floating vegetation mats (Tapley and Acosta-Galvis 2010).

Typhonectes natans is nocturnal, and can be caught free swimming at night (Tapley and Acosta-Galvis 2010).

Parkinson (2004) speculates that T. natans consumes carrion, evident by their presence near riverside fishing villages of northern South America eating gutted fish. These caecilians may also be unpalatable or toxic to predators. In captivity, T. natans consumes earthworms, pre-killed crickets, defrosted mussels and fish, and bloodworms (Barbon et al. 2017).

There are very few studies that have looked at T. natans in the wild despite their reported abundance (IUCN 2020); however, they are common in the pet trade so there are several behavioral studies of individuals in captivity (see "Comments" section below). There have also been numerous studies examining morphological characteristics of T. natans that provide insight into their wild behaviors.

Typhlonectes natans, like all caecilians, have unique jaw mechanics compared to other vertebrates. They have two muscle mechanisms on both sides of the jaw that are used to create a high closing force at varying gape angles. Above a critical gape angle, some muscles will open the jaw and destabilize the jaw joint. These mechanisms allow them to consume prey of various sizes, facilitating their generalist predatory feeding behavior (Kleinteich et al. 2008). Juveniles display a similar feeding mechanism (Kleinteich 2010).

Visual cues are not often associated with caecilians but in T. natans the eyes are secondarily well developed relative to other fossorial caecilian species. The skin that covers the eyes of T. natans is almost transparent and absorbs minimal light in the visible spectrum of 400 - 750 nm. Their rod photoreceptors express Rh1 opsins and show a peak absorbance at 493 nm, which correlates with twilight wavelength and numbers seen in deep-water vertebrates. This suggests that their eyes have evolved for predator and prey detection in deep water when diurnal and nocturnal species are both potentially active (Mohun et al. 2010).

Their nostrils are closed and tentacles are used to detect odors (Vitt and Caldwell 2013).

In addition to foraging, T. natans uses chemosensory as a means of communication. Typhlonectes natans uses chemicals to differentiate between genders, kin, sexual receptiveness, and mate recognition (Warbeck and Parzefall 1997, Wells 2007, Vitt and Caldwell 2013). During non-reproductive periods males and females used chemical signals to aggregate with conspecifics of the same sex, and during the mating season females will actively search for male scented water. Females may be influenced by kin recognition in mating choices, potentially as a means to avoid inbreeding, whereas males are less choosy. Males are not territorial but can be highly aggressive towards other males when they form large aggregations around receptive females for several weeks during the mating periods before copulation (Warbeck and Parzefall 1997, Wells 2007). When males are close to a female they display a head shake behavior followed by mating attempts. When copulation begins, it may last up to four hours. Mating attempts and copulations are rarely interrupted by other males, more often by the female, which suggests that there is female choice in mate selection (Warbeck and Parzefall 1997).

Parkinson (2004) believes T. natans is a dry season breeder that mates annually during the mid-dry season and gives birth early in the dry season the following year. Seasonal temperature fluctuations may be a reproductive trigger (Tapley and Agosta-Galvis 2010). Typhlonectes natans is viviparous and, assumed like Typhlonectes compressicauda, may have between 2 - 10 offspring with a gestation period of 7 - 11 months (Wake 1977, Wake 2015, Parkinson 2004, Reinhard and Kupfer 2022). Female reproductive anatomy consists of a pair of elongated ovaries and a pair of oviducts that differentiate into uteri (Barbon et al. 2017).

These caecilians are a “K” selected species, with a long life span, gestation of approximately 11 months (noted in captivity), late maturity, low rate of reproduction, and high maternal investment (indicated by female/offspring ratio) (Parkinson 2004, Reinhard and Kupfer 2022). Raising young is very energetically expensive for T. natans females. To feed the young, oviductal epithelium proliferates and secretory epithelium produces uterine milk (Wake 1977).

Typhlonectes natans uses lateral swimming undulations to propel themselves through the water. Lateral undulation involves static push-points being used to generate a force vector pointing forward that creates a reactive static friction force. This force launches forward motion of the body (Summers and O’Reilly 1997). Fossorial species use internal vertebral undulations, known as internal concertina, to navigate narrow burrows that do not allow for lateral undulation. Typhonectes natans has completely lost the ability to move via internal concertina, reflective by an inability to move forward in channels that are approximately one body width across, and is likely inefficient in its ability to burrow in the sediment during times of low water (Summers and O’Reilly 1997). This stresses the importance of their migratory pathways to lakes and marshes during the dry season (Tapley and Acosta-Galvis 2010).

Relative to other caecilians T. natans, like other typhlonectids, has very large lungs. This increased lung capacity is likely how T. natans was able to colonize aquatic habitats (Wilkinson and Nussbaum 1999). This caecilian both has a long and well-developed right lung and a tracheal lung between the anterior trachea and heart, which provides more surface area for gas exchange (Wells 2007). Typhlonectes natans uses a unique ventilatory mechanism with bout-breathing mechanics, involving an expiratory phase, inspiratory phase, followed by a long non-ventilatory period. They exhale the contents of their lungs at the surface through a single prolonged exhale, with only the snout tip and nares above the water, and refills them through a series of 10 - 20 buccal pumps (Prabha et al. 2000, Gardner et al. 2000). The first buccal compression cycle is adapted to lung emptying at a large volume, whereas the inspiratory oscillations are specialized for lung inflation (Gardner et al. 2000). This mechanism efficiently eliminates any mixing of expired gasses in the buccal cavity, keeping lung emptying separate from lung filling (Prabha et al. 2000, Gardner et al. 2000). In deep water, hydrostatic pressure is used to help remove gas from their lungs. Their relatively low ventilatory frequency (5 - 8 breaths per hour) may be an adaptation for their seasonally fluctuating habit (Prabha et al. 2000). Breathing frequency increases and inspiratory oscillations per breath decreases during aquatic hypercapnia, whereas breathing frequency increases and inspiratory oscillations per breath increases during aerial hypoxia (Gardner et al. 2000). Pulmonary gas exchange is prominent during exercise recovery, whereas cutaneous gas exchange is prominent during resting, thus sustaining the resting metabolic rates. Skin is the major avenue for CO² elimination (Smits and Flanigan 1994).

This aquatic habitat colonization probably occurred fairly recently as is suggested by its nitrogenous waste excretion. Typhlonectes natans excretes nitrogenous waste in about equal molar quantities of ammonium and urea. Most ammonia and urea is excreted through the skin, rather than kidneys. In general, fully aquatic organisms excrete nitrogenous waste mostly through ammonium, terrestrial organisms excrete nitrogenous waste mostly through urea, and amphibians transition from ammonotelism to ureotelism after metamorphosis. Typhlonectes natans is still transitioning to an aquatic lifestyle, as demonstrated by half of its nitrogen being secreted by urea, whereas most aquatic amphibians secrete most of their nitrogen through ammonia (Stiffler 1994, Wells 2007).

Larva
Fetuses are approximately 40 - 60% of their mother’s total length. When they hatch internally, like T. compressicauda, they develop specialized dentition, featuring flattened crowns topped by a single row of rounded knobs, that changes slightly during ontogeny (Wake 1977, Kleinteich 2010, Wake 2015). Initially, embryos depend on yolk mass, but once exhausted, they feed on secretions and cells from the uterine wall, a process known as prenatal intrauterine feeding (Kleinteich 2010, Barbon et al. 2017, Reinhard and Kupfer 2022). Dentition is used to scrape the oviductal mucosa, and these teeth are shed after birth with adult dentition erupting around 48 hours after birth (Wake 2015).

Neonates of T. natans are about 100 - 150 mm and about 5 mm in diameter (Parkinson 2004, Reinhard and Kupfer 2022). Newborn T. natans may retain their external gills, but will likely lose them within hours after birth (Parkinson 2004, Wake 2015). Larvae of T. natans are precocial, and born with the ability to independently feed (Reinhard and Kupfer 2022).

Larvae have large, sac-like, and paired gills that result from fusion of three rami, which form in the final stages of embryo development (Wake 2015, Barbon et al. 2017). These gills are likely flattened against the oviduct’s mucosal walls. Persumed like T. compressicauda, these gills may be specialized for uptake of oviductal mucosa secretions, such that they are “pseudo-placental”; nutrients are still observed through oral ingestion of oviductal mucosa and secretions as well (Wake 2015).

Trends and Threats
No threats are listed for the Rio Cauca Caecilian, as this caecilian is tolerant of disturbance and some level of degraded habitat (e.g., water pollution) (IUCN 2020). Typhonectes natans has been observed in Venezuela in eutrophic waters contaminated by the oil industry (Gower and Wilkinson 2005, Flach et al. 2020).

Typhonectes natans is the most common caecilian in the pet trade. Despite this they are still abundant in the wild (Gower and Wilkinson 2005, IUCN 2020)

There have been several instances of chytridiomycosis presences in wild caecilian populations (Churgin et al. 2013).

The Rio Cauca Caecilian has been introduced in Florida (Sheehy et al 2021).

Relation to Humans
Typhlonectes natans is one of the most common caecilian species in the pet trade, particularly in Europe and North America, and has been so since 2005 (Gower and Wilkinson 2005, IUCN 2020).

In the wild, these caecilians are commonly found in polluted urban waters, and are often found in fishing villages feeding on discarded fish scraps. Local fishermen in Colombia described catching T. natans with fishing nets and not encountering them during dry seasons.

In Hacienda La Condesa, Columbia, it is said that if a woman’s hair is cut, put into a bottle, and then submerged the bottle, T. natans will appear in the bottle the next day (Tapley and Acosta-Galvis 2010).

Comments

PHYLOGENETIC RELATIONSHIPS:

As of 2024, T. natans is sister to T. compressicauda, the next closest species being Potomotyphylus kaupii, based on Maximum Likelihood analysis on 12S, 16S, and CO1 mitochondrial DNA along with CXCR4, H3, SIA, Slc8a3, and Rag1 nuclear genes (Maciel et al. 2017).

In urban areas of Columbia and Venezuela its local name is "Anguila", which is Spanish for eel (Tapley and Acosta-Galvis 2010). Typhlonectes natans is often mislabeled as a “rubber eel” (IUCN 2020).

OTHER INTERESTING INFORMATION:

General medical problems of captive caecilians are reported to be chytridiomycosis, bacterial and fungal infections, renal failure, liver disease, and nutritional secondary hyperparathyroidism (Barbon et al. 2017). Common causes of death for captive caecilians include renal disease (chronic and affecting tubules or glomeruli) and skin disease (especially oomycete or bacterial dermatitis) (Flach et al. 2020, Kane et al. 2021). In Kane et al. (2021), reproductive and cardiovascular disease was uncommon for their studied population. Skin lesions, poor gut-fill, tissue nodules, granulomas, mineralization, cloacitis, stomatitis, lung lesions, liver lesions, kidney lesions, and gastrointestinal lesions may be observable postmortem in T. natans. Specimens of T. natans with skin lesions may demonstrate excess-abnormal sloughing, skin erosion, and epidermal hyperplasia (Flach et al. 2020). Flach et al. (2020) also observed a variety of micro- and macroparasites in T. natans postmortem, including Aeromonas hydrophilaa, A. hydrophila, Vibrio alginolyticus, Escherichia coli, and nematodes.

There have been two cases of captive T. natans populations being infected by chytridiomycosis, but one population was cured without casualty. There have been several instances of chytridiomycosis in wild caecilian populations (Churgin et al. 2013).

Hartigan et al. (2016) described how only captive populations of T. natans have been observed with infections from the myxozoans C. axonis.

Barbon et al. (2017) described the use of tricaine methanesulfonate solution for caecilian anesthesia, in addition to successful cesarean sections on T. natans.

References
Barbon, A. R., Goetz, M., Lopez, J., and Routh, A. (2017). Uterine rupture and cesarean surgery in three Rio Cauca caecilians (Typhlonectes natans). Journal of Zoo and Wildlife Medicine, 48(1), 164-170. [link]

Churgin, S. M., Raphael, B. L., Pramuk, J. B., Trupkiewicz, J. G., and West, G. (2013). Batrachochytrium dendrobatidis in aquatic caecilians (Typhlonectes natans): a series of cases from two institutions. Journal of Zoo and Wildlife Medicine, 44(4), 1002-1009. [link]

Flach, E. J., Feltrer, Y., Gower, D. J., Jayson, S., Michaels, C. J., Pocknell, A., Rivers, S., Perkins, M., Rendle, M. E., Stidworthy, M. F., Tapley, B., Wilkinson, M., and Masters, N. (2020). Postmortem findings in eight species of captive caecilian (Amphibia: Gymnophiona) over a ten-year period. Journal of Zoo and Wildlife Medicine, 50(4), 879-890. [link]

Gardner, M. N., Smits, A. W., and Smatresk, N. J. (2000). The ventilatory responses of the caecilian Typhlonectes natans to hypoxia and hypercapnia. Physiological and Biochemical Zoology, 73(1), 23-29. [link]

Gower, D. J., and Wilkinson, M. (2005). Conservation biology of caecilian amphibians. Conservation biology, 19(1), 45-55. [link]

Hartigan, A., Wilkinson, M., Gower, D. J., Streicher, J. W., Holzer, A. S., and Okamura, B. (2016). Myxozoan infections of caecilians demonstrate broad host specificity and indicate a link with human activity. International Journal for Parasitology, 46(5-6), 375-381. [link]

Kane, L. P., O'Connor, M. R., Langan, J. N., and Delaney, M. A. (2021). Review of histologic lesions and mortality in rio cauca caecilians (Typhlonectes natans) over a 22-year period. Journal of Zoo and Wildlife Medicine, 52(3), 901-908. [link]

Kleinteich, T. (2010). Ontogenetic differences in the feeding biomechanics of oviparous and viviparous caecilians (Lissamphibia: Gymnophiona). Zoology, 113(5), 283-294. [link]

Kleinteich, T., Haas, A., and Summers, A. P. (2008). Caecilian jaw-closing mechanics: integrating two muscle systems. Journal of the Royal Society Interface, 5(29), 1491-1504. [link]

Maciel, A. O., Sampaio, M. I., Hoogmoed, M. S., and Schneider, H. (2017). Phylogenetic relationships of the largest lungless tetrapod (Gymnophiona, Atretochoana) and the evolution of lunglessness in caecilians. Zoologica Scripta, 46(3), 255-263. [link]

Mohun, S. M., Davies, W. L., Bowmaker, J. K., Pisani, D., Himstedt, W., Gower, D. J., Hunt, D. M., and Wilkinson, M. (2010). Identification and characterization of visual pigments in caecilians (Amphibia: Gymnophiona), an order of limbless vertebrates with rudimentary eyes. Journal of Experimental Biology, 213(20), 3586-3592. [link]

Parkinson, R. (2004). The care and captive breeding of the caecilian Typhlonectes natans. Herpetological bulletin, 2004(88), 8-10. [link]

Prabha, K. C., Bernard, D. G., Gardner, M., and Smatresk, N. J. (2000). Ventilatory mechanics and the effects of water depth on breathing pattern in the aquatic caecilian Typhlonectes natans. Journal of Experimental Biology, 203(2), 263-272. [link]

Reinhard, S., and Kupfer, A. (2022). Maternal investment in the viviparous caecilian amphibian Typhlonectes natans (Gymnophiona: Typhlonectidae). Zoologischer Anzeiger, 296, 33-36. [link]

Sheehy, C., Blackburn, D., Kouete, M., Gestring, K., Laurie, K., Prechtel, A., Suarez, E. and Talley, B. L. (2021). First record of a caecilian (order Gymnophiona, Typhlonectes natans) in Florida and in the United States. Reptiles and Amphibians, 28(2), 355-357. [link]

Smits, A. W., and Flanagin, J. I. (1994). Bimodal respiration in aquatic and terrestrial apodan amphibians. American Zoologist, 34(2), 247-263. [link]

Stiffler, D. F., and Manokham, T. (1994). Partitioning of nitrogen excretion between urea and ammonia and between skin and kidneys in the aquatic caecilian Typhlonectes natans. Physiological Zoology, 67(5), 1077-1086. [link]

Summers, A. P., and O'Reilly, J. C. (1997). A comparative study of locomotion in the caecilians Dermophis mexicanus and Typhlonectes natans (Amphibia: Gymnophiona). Zoological Journal of the Linnean Society, 121(1), 65-76. [link]

Tapley, B., and Acosta-Galvis, A. R. (2010). Distribution of Typhlonectes natans in Colombia, environmental parameters and implications for captive husbandry. The Herpetological Bulletin, 2010(113), 23-29. [link]

Taylor, E. H. (1968). The caecilians of the world: a taxonomic review. Vitt, L. J., and Caldwell, J. P. (2013). Herpetology: an introductory biology of amphibians and reptiles. Academic press. Wake, M. H. (1977). The reproductive biology of caecilians: an evolutionary perspective. In "The reproductive biology of amphibians" (pp. 73-101). Boston, MA: Springer US. [link]

Wake, M. H. (2015). Fetal adaptations for viviparity in amphibians. Journal of Morphology, 276(8), 941-960. [link]

Wake, M. H., and Donnelly, M. A. (2010). A new lungless caecilian (Amphibia: Gymnophiona) from Guyana. Proceedings of the Royal Society B: Biological Sciences, 277(1683), 915-922. [link]

Warbeck, A., and Parzefall, J. (1997). Sex-specific pheromones in the caecilian Typhlonectes natans (Amphibia: Gymnophiona). Advances in Ethology, 32, 137. Wells, K. D. (2019). The ecology and behavior of amphibians. University of Chicago press. Wilkinson, M., and Nussbaum, R. A. (1999). Evolutionary relationships of the lungless caecilian Atretochoana eiselti (Amphibia: Gymnophiona: Typhlonectidae). Zoological Journal of the Linnean Society, 126(2), 191-223. [link]

Zug, G. R., Vitt, L., and Caldwell, J. P. (2001). Herpetology: an introductory biology of amphibians and reptiles. Academic press.

Species Account Citation: AmphibiaWeb 2024 Typhlonectes natans: Rio Cauca Caecilian <https://amphibiaweb.org/species/1964> University of California, Berkeley, CA, USA. Accessed Sep 14, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 14 Sep 2024.

AmphibiaWeb's policy on data use.