A new species of Microcaecilia (Amphibia: Gymnophiona: Caeciliidae) from Guyana
Author
Wilkinson, Mark
Author
Kok, Philippe J. R.
text
Zootaxa
2010
2719
35
40
journal article
10.5281/zenodo.199833
91a4267a-9600-4e24-a71c-2d61a3990722
1175-5326
199833
Microcaecilia iyob
sp. nov.
(
Figs. 1
;
Table 1
)
Gymnopis unicolor
(
Duméril, 1864
)
in part;
Dunn (1942: 471–472)
Microcaecilia unicolor
(
Duméril, 1864
)
in part;
Taylor (1968: 542–546, fig. 297)
Holotype
.
FMNH
35117, a mature male from “Oko River at Cuyuni River”
Guyana
; collected by Neal A. Weber in
June 1936
.
Diagnosis.
A
Microcaecilia
that differs from
M. taylori
Nussbaum & Hoogmoed, 1979
and
M. grandis
Wilkinson
et al.
,
2009
in having fewer PAs (<110); from
M. rabei
(
Roze & Solano, 1963
)
in having fewer PAs undivided by SAGs (<65) and more complete SAGs (> 8); and from
M. albiceps
(
Boulenger, 1882
)
,
M. supernumeraria
Taylor, 1970
, and
M. unicolor
(
Duméril, 1864
)
in having more numerous premaxillary-maxillary teeth (>20) in long series that extend posteriorly beyond the posterior margin of the choanae, and bicuspid vomeropalatine teeth.
Description of the
holotype
. Some morphometric and meristic data are given in
Table 1
. In poor condition in places, incisions extending from CMs across C1 and C2, almost broken into two parts at the 12th PA, less substantial breaks at about 25th and 60th PA, small (
5mm
) midventral incisions just anterior and posterior to second of these breaks, a
12 mm
incision beginning
45 mm
in front of terminus, some open scale pockets and patches of abraded skin, rusty hole on 36th PA another
20 mm
anterior to vent. An arthropodan exoskeletal element embedded in the skin of the lower jaw on the left side. Mature male with multiple large testis lobes.
Body dorsoventrally flattened throughout, relatively uniform, narrowing slightly onto collars anteriorly and more substantially behind the level of the vent; L/W = c. 32. In dorsal view, sides of head straight, converging steadily to level of nares, snout tip between nares rather blunt. In lateral view, top of head weakly convex; margins of upper jaw (lip) concave especially anterior to the level of the TAs; ridge bearing vomeropalatine teeth just visible close to CM; lower jaw half the height of upper jaw at CM. In ventral view, mouth moderately recessed, margins of lower jaw and upper lips not much more blunt than tip of snout. Eyes not visible. TAs very slightly elevated, the elevations visible dorsally and ventrally, lie just above imaginary lines between nares and CMs, distinctly closer to CMs than to nares. Nares small, dorsolateral, circular depressions with anteroventral ovate aperture, somewhat closer to level of AM than to ST, much closer to top than to bottom of snout in lateral view, not visible from below. Teeth pointed, gently recurved, lacking serrations or flanges; elements of outer series much smaller posteriorly, monocuspid, dentaries largest, premaxillary-maxillary teeth large; vomeropalatines much smaller, more uniform in size, bicuspid, about as many in front of the anterior margins of the choanae as behind, vomerine series forming gentle arch anteromedially; distance between vomeropalatine and premaxillary-maxillary series anteriorly almost equal to projection of snout; series converging posteriorly to about half that distance, upper series extending posteriorly well (5–7 elements or more on each side) past choanae, approaching CMs, palatine series extending slightly further posteriorly. Palate moderately arched. Choanal apertures subcircular, separated from each other by twice their individual widths, anterior margins approximately level with tentacles; valves not visible. Tongue simple (no surface architecture) with broad attachment anteriorly. Nuchal region barely more massive than adjacent body. C1 shorter than C2, well-marked, NG1 and NG2 completely encircling body, bending slightly anteromedially on dorsum, NG3 incomplete ventrally; substantial TG on dorsum of C2, just visible laterally. Behind collars, 97 PAs and a small unsegmented terminal cap. AGs slightly raised posteriorly, complete or nearly so dorsally, mostly separated mid-ventrally, 31 AGs complete ventrally anterior to vent; no AGs posterior to vent on venter. First SAG present mid-dorsally on 52nd PA, all PAs behind 55th divided by mid-dorsally complete SAGs, 12 of which are complete ventrally (on PAs 84–95) anterior to vent region. Vent region interrupts last four to five AGs.
Scattered small scales in a single incomplete row present dorsally as far anterior as 25th PA, near terminus scale pockets as deep as the width of a PA, with multiple (8–9) rows of either slightly ovate or rhomboidal (largest 1.0 x
0.8 mm
) scales. No subdermal connective tissue scales. Body terminus acuminate with no indication of terminal keel. In lateral view, ventral surface concave/indented at level of vent. Vent within a fairly discrete, approximately circular, depressed cloacal disc, with slightly transverse opening, its lips formed by about 13 somewhat irregular, short denticulations; a pair of cloacal papillae on anterior denticulations.
Gray-brown, more brown anteriorly and where superficial epidermis missing, darker, more plumbous grey posteriorly, perhaps slightly paler on lateral flanks especially posteriorly where each annulus has a paler anterior and darker posterior half. Head paler than body especially ventrally, except for narrow darker lines approximately level with medial aspect of mandibles, central pale colour extending onto C1. Collar grooves and AGs edged in white, especially laterally. TAs and nares lie within small pale spots. Cloacal disc, including small ventral area of terminal cap, pale.
FIGURE 1.
Preserved holotype of
Microcaecilia iyob
sp. nov.
(FMNH 35117). Scale bar gradations = 1 mm. Arrows indicate first (top) and second (bottom) nuchal collar grooves.
Etymology.
The species is named to commemorate the International Year of Biodiversity (2010) to serve as a reminder that much biodiversity is undescribed and much sampled biodiversity is poorly understood taxonomically. The epithet
iyob
is designated a genderless noun in apposition.
Suggested English common name.
Commemorative
microcaecilia
.
TABLE 1.
Morphometric and meristic data for the holotypes of
Microcaecilia iyob
sp. nov.
and
M. unicolor
and data ranges for a series of
M. unicolor
from French Guiana. All measurements are in mm. Values in parentheses are from Taylor (1968).
|
M. iyob
sp. nov.
Holotype
|
M. unicolor
Holotype
|
| FMNH |
MNHNP ranges |
| Sex |
35117 M |
581 (
n
= 12) F
|
| Total length |
172 (170) |
190 105–201 |
| PAs PAs divided by SAGs |
97 43 (46) |
107 107–117 69 52–74 |
| SAGs complete ventrally |
10 (13) |
44 23–52 |
| Vertebrae Distance between ST and CM |
- 4.2 |
112 112–122 4.3 3.2–5.0 |
| Head width at CM |
4.1 |
3.3 2.5–4.2 |
| Distance between ST and NG1 (laterally) Head width at occiput |
6.2 (6) 4.4 |
5.4 3.8–6.2 3.6 2.9–4.5 |
| Width at mid-body |
5.3 (4.7) |
5.4 2.9–6.0 |
| Distance between ST and AM Body behind vent |
1.1 1.0 |
1.0 0.9–1.5 1.1 0.8–1.6 |
| Intertentacular distance |
3.5 |
2.9 2.3–3.6 |
| Internarial distance Distance between naris and CM |
1.4 3.9 |
1.1 1.0–1.5 4.0 2.9–4.2 |
| Distance between TA and CM |
1.7 |
2.0 1.4–2.2 |
| Distance between naris and lip Distance between TA and lip |
1.1 0.4 |
1.0 0.8–1.1 0.5 0.4–0.5 |
| Distance between TA and naris |
2.5 |
1.9 1.4–2.2 |
| Length of C1 Length of C2 |
1.9 2.4 |
2.3 1.3–2.3 2.4 1.7–2.6 |
| Premaxillary-maxillary teeth |
33 (35) |
16 14–16 |
| Vomeropalatine teeth Dentary teeth |
32 (33) 24 (26) |
25 22–27 20 19–25 |
| Discussion |
Edward Harrison Taylor was by far the most important figure in the history of caecilian taxonomy. In his then comprehensive taxonomic study of caecilians,
Taylor (1968)
provided accounts for some 158 species, of which he was the authority for almost half (73). These and other prodigious feats of species description led to Taylor having a reputation as something of a “splitter”, and a not insubstantial number of his species have been subsequently relegated to synonyms. Although Taylor occasionally explicitly held back from describing possible new species for variant specimens, this was the exception rather than the rule.
In his account of
Microcaecilia unicolor,
Taylor (1968: 544)
gave data for seven specimens from
French Guiana
, including the
lectotype
, and for a single specimen from
Guyana
that is now the
holotype
of
M. iyob
. These data reveal substantial differences in annulation and dentition between the
M. unicolor
from
French Guiana
and the
Guyana
specimen, that result in some very high ranges for these characters in Taylor’s diagnosis of
M. unicolor
. Of these differences
Taylor (1968: 546)
writes only that the
Guyana
specimen “differs in having a primary count of about eight less than the lowest
French Guiana
specimen, and 18 lower than the highest count. The secondaries are reported to be more erratic, varying from 22 to 74? (
fide
Dr. E. R. Dunn), the number of complete secondaries” [sic]. Thus,
Taylor (1968)
was following
Dunn (1942)
in including the
Guyana
specimen with the species
unicolor
, and was perhaps dissuaded from considering the distinctiveness of the
Guyana
specimen within his sample any further by Dunn’s report of a very wide range in secondary annuli. Uncharacteristically,
Taylor (1968)
did not comment on the clear differences in the numbers and disposition of teeth in the upper jaw that are evident in his data and that, by themselves, are strong evidence that the samples from
French Guiana
and from
Guyana
are not conspecific. Two years later, Taylor (1970: 313) highlighted that the
Guyana
specimen differed from the
type
in the number of premaxillary-maxillary teeth and cautioned “Material from this area should be acquired and carefully examined, as I may have erred in so disposing of this specimen.”
Unfortunately,
Taylor (1968)
used the
holotype
of
Microcaecilia iyob
as the basis for his descriptive account of
M. unicolor
and, as
Wilkinson
et al.
(2009)
noted, this has contributed to taxonomic confusion regarding
M. unicolor
(e.g.
Nussbaum & Hoogmoed 1979
).
There are some minor differences between the data reported by
Taylor (1968)
and those reported here on the
holotype
of
Microcaecilia iyob
(
Table 1
). Additionally,
Taylor (1968)
reported that the PAGs are mostly incomplete dorsally whereas we find them to be mostly complete or nearly so, and he also reported that the first and second nuchal grooves curve forward ventrally whereas we find them to be mostly straight (Fig. 21.
A syndrome of dental characters seemingly divides
Microcaecilia
into two groups.
Microcaecilia albiceps
,
the
type
species, and
M. unicolor
have short premaxillary-maxillary teeth series that do not extend posteriorly beyond the choanae, bicuspid vomeropalatine teeth and serrated dentary teeth. The enigmatic
M. supernumeraria
, known only from its
holotype
, appears to belong with these species. It shares the first two of these dental characters but the condition of the third is unknown. Differently,
M. iyob
resembles
M. rabei
,
M. grandis
and
M. taylori
in having long premaxillary-maxillary teeth series and all teeth are monocuspid and unserrated. The new species is readily distinguished from these other
Microcaecilia
by its pattern of annulation with relatively few PAs and many SAGs and consequently relatively small numbers of undivided PAs.
Several museum specimens of
Microcaecilia
that we have seen, including the
holotype
of
M. iyob
,
have pointed and recurved arthropodan exoskeletal remains embedded in the skin of the head. We suspect this is evidence of frequent and aggressive encounters with either ants or termites, and possibly the result of preying upon them.
The new species is known from only a single specimen collected more than 70 years ago and, given that there have been no dedicated attempts to recollect or otherwise survey its status in the wild, it must be considered data deficient for conservation purposes. Targeted fieldwork is needed to shed light on the distribution and abundance of this very poorly known species, and to provide material for both morphological and molecular systematic study.
Microcaecilia iyob
is only the third new species of caecilian described from
Guyana
since
Taylor (1968)
. That these descriptions have appeared within the last two years and have been based on both newly collected (
Wake
& Donnelly 2009
,
Gower
et al.
2010
) and older material (this work), suggests both that the caecilian fauna of
Guyana
remains very incompletely known, and that further species new to science probably remain to be discovered from this region.