Arndt's Torrent-frog, Arndt's Toothed Frog
Species Description: Barej MF, Schmitz A, Penner J, Doumbia J, Sandberger-Loua L, Hirschfeld M, Brede C, Emmrich M, Kouame N'G, Hillers A, Gonwouo NL, Nopper J, Adeba PJ, Bangoura MA, Gage C, Anderson G, Roedel M-O 2015 Life in the spray zone -- overlooked diversity in West African torrent-frogs (Anura, Odontobatrachus). Zoosyst. Evol 91:115-149. Authors of species: Barej, Schmitz, Penner, Doumbia, Sandberger-Loua, Emmerich, Adeba, Bangoura, Gage, Anderson, Roedel.
The forelimbs are robust and muscular. The fingers are slender, and the relative finger lengths are III > IV > II > I. The fingertips are enlarged, triangular in shape, and notched at the center. The nuptial pads are present on finger I, but not very distinct. The subarticular tubercles are present, large, and subconical. The supernumerary tubercles are not present in O. arndti (Barej et al. 2015 Zoosyst).
The hind limbs are also robust and muscular. The femoral glands are enlarged, and are positioned posteroventrally to the femur. On the tibia, there are small circular glands that create a nearly continuous line. Like the fingers, the toes are slender, and the relative toe lengths are IV > III > V > II > I. The toe tips are dilated, triangular, and notched at the center, just like the fingertips. The inner metatarsal tubercle is elliptical and very distinct, but the supernumerary tubercles are absent. Subarticular tubercles are subconical, and distributed across toes I - V as follows: 1, 1, 2, 3, 2 (Barej et al. 2015 Zoosyst).
On the posterior side of the feet, there is a prominent skin fold. The webbing is fully developed, and nearly concave in all extremities, and the formula is (0 - 0/0 - 1/0 - 0.75/0.75 - 0). The flanks and dorsum are covered in ridges. The dorsal skin is granulated, as is the venter (Barej et al. 2015 Zoosyst).
A tadpole description is given by Doumbia et al. (2013) of 16 tadpoles in Gosner stages 25 - 43. The average total length was 36.19 mm, and ranged from 18.3 - 49 mm. The body length averaged 10.75 mm, and ranged from 5 - 15.1mm. The tail length averaged 25.27 mm, ranging from 12.5 - 35.1 mm. The body is flattened dorsolaterally, and appears boxy with a wide, round snout. Larval O. arndti has a large sucker-like oral disc, which allows it to latch onto nearby rocks. The keratodont formula is ⅘. The upper jaw has a wide M-shaped, and lower jaw is in the shape of a large V. The spiracle is located at the mid-body area, and is positioned sinistrally and directed dorsocaudally. It has a long tail with narrow fins that are not very distinct. The dorsal fin is nearly straight, originating at the first quarter of the tail, and its height is about ¾ of the tail’s length. The ventral fin is very narrow, originates from the tail-body junction, and is about the same height as the dorsal fin (Doumbia et al. 2018).
The webbing of O. arndti is similar to O. smithi and O. ziama, although O. smithi has less webbing on the inside of the toe II, and is more extensive than that of O. fouta and O. natator. Odontobatrachus arndti is smaller in snout-vent lenght than O. ziama, but larger in head width, tympanum diameter, orbital diameter, forelimbs, and hind limbs. Odontobatrachus arndti is smaller than O. fouta and O. smithi in snout-vent lenght. The glandular lines of O. arndti have small to average sized glands, which create barely-interrupted lines. Similar to O. arndti, the glandular lines in O. ziama have tiny glands that create nearly-continuous lines. However, the other three species differ significantly. The glands of O. fouta vary greatly in size, from small to large, and are interrupted. The glands of O. natator vary similarly in size, and are also fairly interrupted. The glands of O. smithi are small to average in size, and are mainly interrupted (Barej et al. 2015 Zoosyst).
In life, dorsal coloration varies from almost black and beige with longitudinal reddish-brown spots in a line. Male femoral glands are yellow (Barej et al. 2015 Zoosyst).
In preservative, the dorsum and hind limbs of O. arndti are dark brownish, and are marbled with lighter brownish streaks. The throat of O. arndti is colored inversely to the dorsum: pale brown with dark brownish marbling. The rest of the coloration of O. arndti is pale, with some small markings along the femoral glands (Barej et al. 2015 Zoosyst).
In life, larval O. arndti are light to dark brown with lighter yellowish and black spots all over. There are sometimes orange spots present on the flanks, back, and dorsal tail, but not on the ventral side of the tail. The tip of the tail is sometimes white (Doumbia et al. 2018).
In preservative, the flanks and dorsum of larval O. arndi are light brown with occasional darker brown spots of different sizes. These spots are usually more visible towards the eyes, nostrils, and tail tip. The flanks, venter, and tail tip are whitish, the tail fins are grey, and the tail has a dark line along its axis (Doumbia et al. 2018).
There appears to be sexual dimorphism in O. arndti as females tend to be much larger in overall size than male. However, the proportions are quite similar between males and females. Males also have secondary sexual characters in the form of femeral glands, velvety nuptial excrescences on finger I, and vocal sacs. In both sexes, the webbing formula varies on toe IV with a maximal height of half way up the toe on both sides. The number of dorsal ridges also varies, from 3 - 6 ridges. The coloration of O. arndti, both dorsally and ventrally, varies from lighter shades of brown to darker, and doesn’t seem to be sex-dependent (Barej et al. 2015 Zoosyst).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Cote d'Ivoire
Life History, Abundance, Activity, and Special Behaviors
At its southernmost range at the base of the Nimba Mountains, O. arndti occurs syntopically with O. natator (IUCN 2019)
Trends and Threats
The species is found in some protected areas: Mount Sangbé National Park in Côte d’Ivoire and Mount Nimba UNESCO Biosphere Reserve in Guinea and Côte d’Ivoire. However, habitat conservation and more surveys are needed to determine the true extent of the species range (IUCN 2019).
Possible reasons for amphibian decline
General habitat alteration and loss
Initially, the Odontobatrachus genus was composed of only O. natator, after its distinction from the Petropedetes genus in 2013 (Barej et al. 2015 Zoosyst). However, in 2015, Barej et al. (Zoosyst) found that the Odontobatrachus genus was actually composed of 5 distinct species: Odontobatrachus arndti, O. fouta, O. natator, O. smithi, and O. ziama. By phylogenetic analysis of the 16S, 12S, cyt b mitochondrial genes, and BDNF, SIA, and rag1 nuclear genes, it was found that O. arndti is sister to O. ziama. The clade formed by these two species is sister to O. natator, and the clade formed by these three species is sister to a clade formed by O. fouta and O. smithi (Barej et al. 2015 BMC).
The genus Odontobatrachus is a combination of two Greek words: “Odous,” which means “tooth,” and “batrachos,” which means “frog.” This name is a reference to the long maxillary teeth and lower jaw tusks of O. natator and its, at the time, undescribed congener (Barej et al. 2014).
The species name “arndti” was chosen to honor Dr. Rudolf G. Arndt, a professor who greatly supported studies of the Odontobatrachus genus (Barej et al. 2015 Zoosyst).
Barej, M. F., Penner, J., Schmitz, A., Rödel, M.-O. (2015). ''Multiple genetic lineages challenge the monospecific status of the West African endemic frog-family Odontobatrachidae.'' BMC Evolutionary Biology, 15(67).
Barej, M. F., Schmitz, A., Penner, J., Doumbia, J., Sandberger-Loua, L., Hirschfeld, M., Brede, C., Emmrich, M., Kouamé, N. G. G., Hillers, A., Gonwouo, N. L., Nopper, J., Adeba, P. J., Bangoura, M. A., Gage, C., Anderson, G. and Rödel, M.-O. (2015). ''Life in the spray zone – overlooked diversity in West African torrent-frogs (Anura, Odontobatrachidae, Odontobatrachus).'' Zoosystematics and Evolution, 91(115-149).
Doumbia, J., Sandberger-Loua, L., Schulze, A., Rodel, M-O. (2018). ''The tadpoles of all five species of the West African frog family Odontobatrachidae (Amphibia, Anura).'' Alytes, 36 (1-4), 63-92.
IUCN SSC Amphibian Specialist Group. 2019. Odontobatrachus arndti. The IUCN Red List of Threatened Species 2019: e.T89113671A96091824. https://dx.doi.org/10.2305/IUCN.UK.2019-1.RLTS.T89113671A96091824.en. Downloaded on 05 March 2021.
Originally submitted by: Alice Drozd (2021-03-06)
Description by: Alice Drozd (updated 2021-03-06)
Distribution by: Alice Drozd (updated 2021-03-06)
Life history by: Alice Drozd (updated 2021-03-06)
Trends and threats by: Ann T. Chang (updated 2021-03-06)
Comments by: Alice Drozd (updated 2021-03-06)
Edited by: Ann T. Chang (2021-03-06)
Species Account Citation: AmphibiaWeb 2021 Odontobatrachus arndti: Arndt's Torrent-frog <https://amphibiaweb.org/species/8370> University of California, Berkeley, CA, USA. Accessed Oct 27, 2021.
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Citation: AmphibiaWeb. 2021. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 27 Oct 2021.
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