Taxonomic treatment Open Access
Wilkinson, Mark; Reynolds, Robert P.; Jacobs, Jeremy F.
Holotype. United States National Museum of Natural History, Smithsonian Institution (USNM) 320729, a female collected by Jeremy F. Jacobs and Robert P. Reynolds from Finca Virgen La Dolores, at km 57 sign on Hollin-Loreto Road (E20), Orellana, Ecuador, c. 0 degrees 43' 50" South and 77 degrees 30' 25" West,and c. 1000m above sea level, 16th August 1990. According to the map available at the time (titled "Republica Del Ecuador" and "Compilado Por El Instituto Geografico Militar," Escala 1:1'000.000, published by the Ministerio De Relaciones Exteriores in Quito, Ecuador, dated 9 November 1981), the type locality, which was in the Province of Napo (Orellana having been established in 1998), is in the vicinity of the "Cordillera Galeras" and featured hillsides through cutover forest with abundant epiphytes. The "Hollin-Loreto road" was not on the map but was provided by the driver, Ramiro Donoso. This is shown as E20 on modern maps.
Diagnosis. As for the genus.
Identification. Based on external morphology alone, the new species is readily distinguished from all other rhinatrematids by having very few (less than four) annular grooves interrupted by the vent. Further, the combination of low number of annular grooves (<275) and its uniform colour distinguishes it from all other rhinatrematids except E. colombianus (Rendahl & Vestergren, 1938), the only known specimen of which has even fewer annular grooves (<225).
Description of holotype. Good condition, an c. 20 mm midventral longitudinal incision c. 30 mm anterior to tail tip, some open scale pockets, mouth preserved open. Total length 173 mm. Body subcylindrical, mostly somewhat dorsoventrally compressed (at midbody: width 7.3 mm, depth 4.5 mm, circumference 20 mm), less so posteriorly, not compressed (width 4.0 mm, depth 4.0 mm) at level of vent, fairly uniform,narrowing slightly anteriorly and more notably posteriorly. Tail moderately long, 7.6 mm, slightly laterally compressed, 3.0 mm wide and 3.5 mm deep c. half way between vent and tail tip, tapering more strongly in dorsal than in lateral view, tip much more broadly blunt in lateral than in dorsal view, dorsal and ventral margins symmetrical in lateral view, ventral surface not flat.
Head 7.0 mm from snout tip to corner of mouth, 9.0 mm from snout tip to first nuchal groove behind corner of mouth, in dorsal view slightly more V- than U-shaped, dorsoventrally compressed, as wide (6.1 mm) and deep (4.9mm) as adjacent nuchal region posteriorly,narrowing gently anteriorly up to about a third of the way between eyes and nares in front of the eyes. In ventral view, lower jaws virtually as wide as head, tip more bluntly rounded than snout anteriorly, mouth marginally subterminal (anterior of mouth to snout tip 0.7 mm). In lateral view, head tapers very gently anterior to eye level, sharply from level of nares, edges of mouth (lips) fairly straight, slightly downturned at corner of mouth, corner of mouth slightly further from top than from bottom of head,lower jaws robust, almost as deep as upper jaws at eye level.
Circular eyes small (diameter 0.4 mm), central grey lens and darker periphery clearly visible through skin, elevated above adjacent skin, equidistant from top of head and lip in lateral view, inset by almost one diameter from outline of head in dorsal view. Tentacular apertures small (0.6 mm) almost horizontal arc-like slits, curving ventrally at their ends, extending anteriorly from the middle (i.e., at three o’clock) of the anterior edge of eye, their margins slightly elevated, the tips of the paired tentacular ducts of each side (leading from the tentacle to the vomeronasal organ) visible through the skin adjacent to the anterior end of the tentacular apertures. Nares small (0.3 mm), subcircular on lef, more tear shaped on right, deeper and broader anteriorly,visible dorsally inset about one and a half diameters from outline of head; in lateral view, slightly closer to tip than to top or bottom of snout; slightly closer to lips (0.7 mm) than are eyes (0.8 mm), visible in anterior but not ventral views. Distance between nares (1.5 mm) half the distance from naris to eye (3.0 mm).
Teeth pointing posteriorly (at angles of 30˚ to 45˚ from the jaws), not strongly recurved, bicuspid, anterior and posterior teeth of each series smaller than those in between, none hypertrophied, outer mandibular (“dentary”) teeth (36) generally a little larger than opposing premaxillary-maxillary teeth (42) and vomeropalatine teeth (40), inner mandibular (“splenial”) teeth (24) a little smaller. Curvature of premaxillarymaxillary tooth series following that of upper lip, vomeropalatine tooth series straighter except anteriorly, extending slightly (about three teeth on each side) beyond the last premaxillary-maxillary teeth, distance between upper series narrowing posteriorly, maximal laterally (about the level of half way between the eye and the naris). Inner mandibular tooth series straightening a little anteromedially, much shorter than the outer mandibular series, about one quarter of the length of the outer mandibular tooth series (about six teeth on each side) posterior to the last inner mandibular teeth.
Based on the CT scan there are nine premaxillary teeth (five right, four lef), 33 maxillary teeth (17 right, 16 lef) for a total of 42 premaxillary-maxillary teeth, 13 vomerine (six right, seven lef) and 26 palatinal teeth (12 right, 14 lef, two on each side posterior to the last maxillary teeth) for a total of 39 vomeropalatine teeth, 37 outer mandibular teeth (19 right, 18 left) and 22 symmetrically disposed inner mandibular teeth, with seven (right) and eight (left) outer mandibular teeth behind the level of the last inner mandibular teeth. Although not identical, numbers of teeth determined from CT scans are reassuringly similar to direct counts.
Tongue with more or less longitudinal plicae over entire surface, margin free not covering any inner mandibular teeth, sides forming an angle of c. 100° anteriorly. Choanae elongate, much longer than wide, distance between them more than eight times their maximal transverse diameters, posterior limit about level with middle of the eye. Palate without plicae.
First groove in the collar region (interpreted as first nuchal groove) poorly marked on dorsum and dorsolaterally, not visible in ventral view. Second nuchal groove faint dorsally, pale and clearly marked laterally and ventrally.Third nuchal groove complete,bows slightly anteromedially on the dorsum and resembles subsequent annular grooves. First nuchal collar much shorter (1.2 mm) than the second (4.5 mm). Four regularly spaced dorsal transverse grooves on second collar bowing slightly anteromedially and of slightly increasing length all ending dorsolaterally. Behind the collars 247 annular grooves,those in the first third and last sixth orthoplicate, otherwise slightly angulate (curving posteromedially) on venter except last complete annular groove before the vent which curves anteromedially mirroring the anterior limit of the disc. First and last (c. 15-20) annuli are a little longer than others. Annular grooves are complete ventrally except for two interrupted by the vent and disc, tail (area behind the vent) with ten complete and one (the last) dorsoventrally incomplete annular grooves.
A single row of small subcircular scales present in shallow pockets (about one quarter the length of a midbody annulus) below the dorsal transverse grooves on the second nuchal collar. At midbody and posteriorly, scales occur in two well-defined rows, a posterior row of larger scales (e.g., 1.1 x 1.0 mm) and an anterior row of slightly smaller scales, in pockets about as deep as the length of an annulus at midbody, about one and a half times the length of an annulus posteriorly. Additional scattered scales may lie below (posterior to) the row of larger scales. The two rows of scales in posterior annuli can be clearly discerned in the CT scan of the tail end (Fig. 4), which reveals that apart from the last rows, scales mostly form complete transverse rings around the body and tail except where these and the associated annuli are interrupted by the vent. Scales in a single row overlap with their neighbours. Midventral scales are superficial to the proximal edges of the adjacent scales on each side, the distal edges of which are superficial to the proximal edges of the succeeding adjacent scale and so on until some mid-dorsal scale with edges that are deep to both its neighbours. Successive scale rows are offset in a brick layout (i.e., shifed half a scale in the transverse direction).
Vent slightly longitudinal, bordered by an irregular array of partially subdivided denticulations, perhaps two pairs and one posteromedial denticulations posteriorly, posterior denticulations pigmented and glandular like the adjacent skin especially peripherally, anterior denticulations, pale, with shorter interdenticular grooves. There is no disc other than what is delimited by the denticulations around the vent, approximately eggshaped with the narrow apex anterior formed by the unpigmented denticulations. No indication of papillae. Very small ovarian eggs (largest c. 0.8 mm diameter) are visible towards the front of the ventral incision.There are no melanophores in the viscera.
Almost uniformly dark, brownish lavender, slightly paler on the head, more so on throat. Pale areas around eye, a slightly paler snout tip encompassing nares. Pale, narrow, faint paramandibular stripes (inset from lips) on ventral surface of head, distinctive pale second nuchal groove on ventral collar region. Paler around vent, especially anteriorly. Annular grooves with a light posterior margin and typically slightly longer anterior dark, aglandular area.
Other than the osteological features that distinguish Amazops amazops sp. nov. from the species of Rhinatrema and Epicrionops, the skull and mandibles are typically rhinatrematid (Nussbaum, 1977). Thus they are zygokrotaphic, with the characteristic squamosal notch and associated process of the os basale and medial parietal ridges providing part of the origin of the primary adductor musculature. There are separate septomaxillae but prefrontals and postfrontals are lacking. The os basale forms a continuous bony dorsal margin of the foramen magnum and a well-developed parasphenoidal rostrum separates the vomers. The retroarticular processes of the mandibles are relatively short and straight, not curving medially or dorsally. Different from what has been reported for other rhinatrematids (Nussbaum, 1977; Reiss, 1996), the pterygoids are large and single on each side with posterodorsal processes closely adpressed to the quadrates and there is no indication of any pterygoid process of the quadrate. There are 77 vertebrae of which the last seven are entirely posterior to the vent and differ from more anterior vertebrae in bearing some indication of haemal arches associated with the parasphenes. Bony ribs are absent from the last four of these caudal vertebrae.
Remarks. That the species is known from a single specimen is sufficient reason to suggest that the IUCN conservation status of the species should be data deficient. Effort is needed to identify populations of this distinctive lineage as a precursor to any meaningful study of its natural history. Based on it being a rhinatrematid it is assumed that it will share the reproductive mode of the other rhinatrematids, as far as is known, in being oviparous with an aquatic larval stage (San Mauro et al., 2014, Müller, 2020) and thus being dependent on water bodies for its reproduction.
Etymology. As for the genus. For nomenclatural purposes the specific epithet is considered to be a genderless noun in apposition.
Nussbaum, R. A. (1977) Rhinatrematidae: A new family of caecilians (Amphibia: Gymnophiona). Occasional Papers of the Museum of Zoology, University of Michigan 682, 1 - 30.
Reiss, J. (1996). Palatal metamorphosis in basal caecilians (Amphibia: Gymnophiona) as evidence for lissamphibian monophyly. Journal of Herpetology 30, 27 - 39.
San Mauro, D., Gower, D. J., Muller, H., Loader, S. P., Zardoya, R., Nussbaum, R. A. & Wilkinson, M. (2014) Life-history evolution and mitogenomic phylogeny of caecilian amphibians. Molecular Phylogenetics and Evolution 73, 177 - 189. DOI: 10.1016 / j. ympev. 2014.01.009
Muller, H. (2020) Development and demography of larval Epicrionops bicolor (Amphibia: Gymnophiona: Rhinatrematidae), Neotropical Biodiversity 6, 98 - 108. DOI: 10.1080 / 23766808.2020.1756131]
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