Hypogeophis pti, Gower, 2017

Gower, David J., 2017, A new species of small and highly abbreviated caecilian (Gymnophiona: Indotyphlidae) from the Seychelles island of Praslin, and a recharacterization of Hypogeophis brevis Boulenger, 1911, Zootaxa 4329 (4), pp. 301-326 : 313-320

Hypogeophis pti sp. nov.

urn:lsid:zoobank.org:pub:02AA8E2E-FA54-4C32-ACA9-3890C3839C8C ( Figs. 1 , 7 , 9–11 ; Table 2)

Holotype. BMNH 2005.1825 ( Figs. 7 , 9 ), adult female, collected from Fond Peper region of Praslin National Park, Praslin island, Seychelles (04°20’04.9”S, 055°44’24.9” E, ca. 178 m /asl) by S.T. Maddock on 4 February, 2014.

Paratypes (n = 13). BMNH 2005.1826–1833 (3 females: 4 males: 1 sex not determined) collected from Fond Peper region of Praslin National Park, Praslin island, Seychelles (04°20’04.9” S, 055°44’24.9” E, ca. 178 m /asl) by S.T. Maddock on 22 March 2013 (2005.1826), 3 February 2014 (2005.1830–1832), 4 February 2014 (2005.1827) and 5 February 2014 (2005.1828–1829, 2005.1833) . BMNH 2005.1834–1837 (2:0:2) collected from Glacis Noir (adjacent to Fond Peper ) region of Praslin National Park, Praslin island, Seychelles (04°20’23.3” S, 055°44’37.5” E, ca. 342 m /asl) by S.T. Maddock, D.J. Gower and Julia J. Day on 13 February 2014 . BMNH 2005.1838 , adult female, collected from Ma Katrine , Praslin Island, Seychelles (04°20’43.9” S, 055°44’36.7” E, ca. 333 m /asl) by S.T. Maddock, D.J. Gower and Matthieu Labuschagne on 5 March 2014 (see Fig. 1 ).

Referred specimen (n = 1). BMNH 1987.2109, adult female, from “Granitic Seychelles, probably Mahé ”. This is considered a referred rather than paratype specimen because it lacks precise locality data.

Diagnosis. A Hypogeophis with fewer than 70 vertebrae. Differs from its most similar congener ( H. brevis : 71–75 vertebrae in available sample: Fig. 8 ) in having tentacular apertures relatively closer to the eye (E-TA/E-N 0.5–0.63 versus> 0.75 in known specimens: Fig. 8 ). See below for information on substantial morphometric and genetic differentiation between the two species.

Identification. The new taxon is a species of Hypogeophis because (following the generic diagnosis provided by Wilkinson et al. 2011) it is an indotyphlid with eyes not covered by bone, tentacular grooves covered by bone, and mesethmoid not exposed dorsally between frontals (data from microCT scans, not shown). It differs from species of the other Seychelles genera ( Praslinia , Grandisonia ) in having a small pointed head and far anterior tentacular apertures, anterior to the mouth. The new species differs from H. rostratus most obviously in having secondary annular grooves on most primary annuli (versus on only posteriormost primary annuli) and in having fewer than 95 vertebrae.

Grandisonia diminutiva Taylor, 1969 was described based on a holotype and paratype from an unspecified locality (or localities) on Praslin. Both specimens are small, with reported total lengths of 95 and 64 mm, respectively. We are confident that Taylor’s species is not the same as H. pti sp. nov. because there are substantial differences in the number of PAGs (80–83 versus 61–64), and in the number of anterior PAs without SAGs (>10 versus 0). Grandisonia diminutiva was placed in the synonymy of G. sechellensis ( Boulenger 1911) by Wilkinson & Nussbaum (2006).

Description of holotype. Some meristic and morphometric data are given in Table 2. Condition good; ca. 10 mm longitudinal ventral incision into coelom ca. 24 mm anterior to vent, another ca. 4 mm incision ca. 50 mm anterior to vent; mouth preserved slightly open with head flexed upwards forming a dorsal fold at NG1; constriction of body ca. 50 mm anterior of vent caused by field tag string; broad, shallow midventral groove on anterior half of body; small sections of few scale pockets opened dorsally.

_antvent = incomplete AGs immediately anterior to vent and disc; AG_incomp = incomplete AGs in vicinity of vent and disc; LT = tip of lower jaw; MC = midbody circumference;

PAG_SAG = PAGs anterior to first SAG; PAG_SAGd = PAGs anterior to first dorsally complete SAG; PAG_SAGv = PAGs anterior to first ventrally complete SAG; TL = Total length; WH = maximal width of head; WM = width at midbody. See Materials and Methods for other abbreviations. Values separated by comma are given in left, right order. * indicates holotype; all other individuals are paratypes except specimen BMNH 1987.2109 (referred specimen). Tooth counts in parentheses are from x-ray CT reconstructions.

2005. 2005. 2005. 2005. 1987. 2005. 2005. 2005. 2005. 2005. 2005. 2005. 2005. 2005. 2005. Specimen 1825 * 1827 1835 1837 2109 1826 1838 1829 1832 1834 1836 1833 1828 1830 1831 Slightly dorsoventrally compressed, uniform throughout except for tapered posterior- and anteriormost (including head) ca. 10 mm. Head small, head length less than midbody width, head width much less than body width. In dorsal view head strongly V-shaped, sides straight and converging substantially from back of head to distinct bulges of TPs, continuing with straight edges in front of TAs to narrowly rounded snout tip. In ventral view lower jaw and upper lip slightly more broadly rounded than snout, upper jaws visible from slightly anterior to CMs forwards. In lateral view upper lip slightly concave, apex approximately halfway along lip; lower lip straight. Snout very prominent in lateral view, projection anterior to mouth more than half as long as upper lip.

Eyes slightly inset from edges of head in dorsal view (by distance less than diameter of eye), approximately halfway between snout tip and back of head; faintly visible as dark spots; much larger than TAs, slightly larger than TPs. TAs subcircular to oval, approximately on (right) or slightly below (left) imaginary lines between nares and CMs; closer to imaginary lines between eyes and nares than to lips; closer to lip than to nares. In lateral view, CMs closer to bottom than top of head. Nares oval, in lateral view approximately equidistant from top, bottom, tip of snout. In dorsal and ventral views nares not visible. TPs visible in dorsal and ventral views, TAs not visible dorsally.

All teeth bicusped, PMs extend only a short distance posterior to choanae; PM row slightly longer than VP row (though extending less far posteriorly). No diastema between vomerine and palatine teeth. The distance between PM and VP rows anteriorly approximately one third of the distance AM-ST. Palate only slightly concave transversely, generally pale but slightly pigmented anterior to choanae. Tongue unattached anteriorly, tip rounded and slightly darker, plicae very few and restricted far posteriorly, no distinct posterolateral grooves, narial plugs large and prominent with clearly delimiting grooves medially. Choanae subcircular, interchoanal distance approximately one and a half times the width of each choana, valves not deeply set (visible).

C2 slightly more massive than first PA, C1 less massive than C2, more massive than back of head. C1 approximately same length as first PA, distinctly shorter than C2. NG1, NG2 and NG3 clearly marked and complete, generally orthoplicate, NG1 and NG2 with slight anterior bend ventrally (where each is slightly thicker), NG3 with slight posterior bend both dorsally and (more clearly) ventrally. Two TGs clearly indicated on C2, both extend across more than half width of dorsum, anterior TG more extensive, almost to edges of C2.

AGs clear but not very conspicuous to naked eye, slightly more conspicuous posteriorly; under microscope well marked throughout. PAGs complete throughout, SAGs dorsally complete throughout, midventrally narrowly incomplete on anterior two fifths, complete from 18th PA. No substantial regional variation in lengths of PAs. SAGs on all PAs. AGs generally orthoplicate, approximately 12 posteriomost AGs with slight anterior bend ventrally. Each AG with irregular row of closely packed, pale, small and larger glands posterior to narrow darker band. Posterior edges of annuli increasingly raised posteriorly, thin whitish line (scales) appears between darker band and paler glands, whitish line not visible on anterior one quarter to one third of body.

Posteriorly (within 15 AGs from TT) four rows of scales in pockets as deep as approximately two thirds to three quarters the length of a PA at this point; anteriorly (15 PAGs behind collar region) three scale rows in pockets approximately half to two thirds the length of a PA. All observed scales oval, wider than long.

Small terminal cap, slightly longer than three quarters length of adjacent PAs. Posteriormost AG transversely narrow, restricted to dorsum, approximately level with back of disc surrounding vent. No AGs on venter behind centre of the vent. Terminus bluntly rounded, much more so than head; inconspicuous terminal ‘keel’ visible as pale narrow line from behind disc onto posteroventral surface of TT. Disc not well circumscribed, subcircular (diameter ca. 1.2 mm), very slightly depressed, with nine (four posterior, two lateral, three anterior) fairly bilaterally symmetrical denticulations, those lateral and posterior longest, those posteromedial much the largest; vent circular to slightly transverse, somewhat V-shaped.

Body brown to brown-grey in preservative, uniform along length, notably paler ventrally, meeting darker middorsal band, transition fairly abrupt and lying more dorsolaterally than laterally, except last 10 mm where darker dorsum progressively more ventrally extensive. Disc pale with grey flecks on all denticulations, not extending to their edges. Head greyish brown, more grey than adjacent body. Faint, slightly pale patch barely broader than eye taper and extend anteriorly towards TPs as very inconspicuous eye-tentacle stripes (less inconspicuous on left). ST pale, abruptly whitish dorsally; underside of rostrum whitish anteriorly, grey posteriorly. Nares entirely within whitish area of snout tip; TPs pale. Pale upper and lower lip lines. Broad pale irregular stripes on ventrolateral surfaces of mandibles, separated from pale lip line by irregular greyish band.

Variation among paratypes. Thirteen paratypes, condition generally good. Posterior part of body missing in BMNH 2005.1827; skin damaged dorsally (outer layer missing in parts) and scale pockets open approximately three quarters along length of BMNH 2005.1838. Paratypes agree with description of holotype presented above with following exceptions (see Table 2 for variation in quantitative characters).

Body shape in many specimens less uniform along length than in holotype, especially in larger specimens (BMNH 2005.1834, BMNH 2005.1838, BMNH 2005.1826), in which anterior third of body gently tapered, notably narrower than posterior half. In lateral view upper lip much less notably concave in smaller specimens; eye less visible in larger specimens; TAs on or slightly below imaginary line between naris and CM.

PMs extend further posteriorly and VP rows more angulate anteriorly than in the holotype in BMNH 2005.1835, 1837 and 1838. There is a small gap in the VP series immediately anterior to the choana on the right side only in BMNH 2005.1827. There is substantial variation in the size of the narial plugs and of the choanae, with the distance between the latter ranging from about 1.25 times (in BMNH 2005.1827) to 2 times (BMNH 2005.1834) the width of the choanae. Choanal valves are slightly more deeply set than in the holotype in BMNH 2005.1834. Posterolateral grooves are present or not on the tongue. Pigment is present on the palate and/or tongue or completely absent.

NG1 orthoplicate dorsally in BMNH 2005.1831; NG3 anteriorly bowed midventrally in BMNH 2005.1835; NG3 narrowly incomplete midventrally in BMNH 2005.1834, BMNH 2005.1826, BMNH 2005.1837, BMNH 2005.1829, BMNH 2005.1831. Three TGs on C 2 in BMNH 2005.1835, anteriormost least conspicuous, middle one most extensive; some specimens with only one TG on C2 ( Table 2); BMNH 2005.1835 with row of glands in TG-like line on dorsum of C1.

Some PAGs incomplete midventrally on anterior half of body in BMNH 2005.1831, BMNH 2005.18270, BMNH 2005.1834, BMNH 2005.1835 and especially BMNH 2005.1838. Approximately 8–14 posteriomost AGs with slight anterior bend ventrally.

Posteriormost AG encircles more of the body in BMNH 2005.1828, BMNH 2005.1826, BMNH 2005.1834, BMNH 2005.1835; groove approximately level with centre of vent in BMNH 2005.1837; terminal cap up to almost one and a half times the length of the posteriormost PA in these same specimens except BMNH 2005.1828. Body terminus more pointed in BMNH 2005.1832. The keel-like line on the posteroventral surface of the terminus is sunken rather than level in many specimens (e.g., BMNH 2005.1831).

Head not more grey than body in some, smaller specimens (e.g., BMNH 2005.1830, BMNH 2005.1829, BMNH 2005.1837, BMNH 2005.1833). Little variation in clarity and extent of pale line between eye and TA. Snout tip of BMNH 2005.1826 less pale and transition to pale tip less abrupt. Greyish band on mandibles absent in BMNH 2005.1838, BMNH 2005.1826. Extent of dark flecks on disc surrounding vent varies ( Fig. 10 ).

Etymology. The specific epithet is in reference to the very small size of the species, one of the smallest of known caecilians. ‘Pti’ is a typical spelling in Seychellois Creole of the French petit/petite (small, in English). For nomenclatural purposes the specific epithet is considered to be a noun in apposition.

Suggested ‘common’ name. Petite Praslin caecilian.

Distribution, natural history, and conservation. Hypogeophis pti sp. nov. is known only from Praslin National Park (Fond Peper and Glacis Noir) and Ma Katrine, at approximately 170–350 m elevation, on the island of Praslin. The 14 type specimens were collected during approximately 29 person hours of dedicated caecilian fieldwork in 2013 and 2014. Two additional specimens (not included in this study) were collected by S.T.M, D.J.G and M.W. during 105 person minutes of digging in Fond Peper on 3 March 2014; one of the animals escaped and the other (field tag MW 10584) is among unaccessioned material in the care of the Seychelles Natural History Museum. In another ca. 19 person hours in 2013 and 2014 no further specimens were found at six other localities on Praslin, including in the Valée de Mai, Nouvelle Decouverte, close to the peak of Mount Takamaka, Fond Ferdinand, Zimbabwe, between Anse Kerlan and Zimbabwe, Grand Anse, and between Anse Takamaka and Anse La Blague. No specimens of H. pti sp. nov. were found on Praslin during surveys in 1976, 1977, 1978, 1983 and 1991 at Grand Anse, Anse Bois de Rose, La Point, La Plaine Hollandaise, Ford Azore, Baie Sainte Anne, Vallée de Mai and Nouvelle Decouverte.

In Fond Peper, specimens of Hypogeophis pti sp. nov. were found among vegetation dominated by pandanus ( Martellidendron hornei (Balf.f.) Callm. & Chassot) and coco de mer ( Lodoicea maldivica (J.F.Gmel) Pers. ). All specimens were collected from within ca. 30 m from the nearest water source (streams and/or seepages) and within ca. 3 m of the nearest tree. Specimens were dug from under dense and horizontally expansive layers of dried (especially pandanus) leaves, in clay, silty clay loam or sandy loam soils of pH 5.46–5.64. The specimens were found in the top ca. 15 cm of soil, which often lay immediately below a thin layer of rootlets. In Glacis Noir, specimens were found in a small area, within ca. 10 m of the only small stream/seepage that we found. The vegetation was more mixed here, with a canopy of broadleaf trees as well as coco de mer and other palms. There was also more understorey vegetation than in Fond Peper, and a lack of the thick layer of pandanus leaves that characterised the latter habitat. Specimens here were found mostly in clay loam soil with dense layers of root mat (pH 4.1–5.76) with one specimen (BMNH 2005.1834) collected from within a rotten log. In Ma Katrine, the specimen was found in a marshy area under a canopy dominated by the pandanus M. hornei .

Although it inhabits protected habitat within a National Park, Hypogeophis pti sp. nov. has a very small known distribution. Because the known distribution is smaller than that known for the Seychelles caecilians H. brevis and Praslinia cooperi , and because it is known from one or, at most two, threat-defined locations, the new species would qualify for at least Endangered status on the IUCN Red List if there is any evidence of decline in extent or quality of habitat or declines in numbers of individuals. However, given that H. pti sp. nov. occurs partly in a protected area and that there is no immediate prospect of estimating or monitoring numbers of individuals, it might be expected to be classified, for now, as Near Threatened. Most of our recent fieldwork within the Praslin National Park took place in and above Fond Peper. We would be surprised if H. pti sp. nov. was entirely absent from the adjacent Vallée de Mai (though we failed to find it in ca. 9 person hours of digging there), as well as more widely within the upper slopes of the La Prude catchment surrounding Ma Katrine. Almost nothing is known of the ecology of H. pti sp. nov., and more studies in the field and/or captivity are required to generate even the most basic data on, for example, reproduction and life history mode.

Figures

FIGURE 1. Maps showing sampling distribution: (a) Mahé Hypogeophis brevis (grey symbols): circles indicate collecting localities between 2013 and 2015 (BMNH), and triangles indicate approximate collecting localities between 1976 and 1991 (UMMZ), and (b) Praslin H. pti sp. nov. (red symbols).

FIGURE 7. Holotype of Hypogeophis pti sp. nov. (BMNH 2005.1825). Scale bar increments in mm.

FIGURE 8. (a) Histogram depicting the frequency of the number of vertebrae, (b) box plot summarising variation in the ratio between eye-tentacle / eye-naris distances for Hypogeophis brevis (grey) and H. pti sp. nov. (black), (c) Principal components analysis (PCA), and (d) principal coordinate analysis (PCoA) for all head measurements for H. brevis (grey circles) and H. pti sp. nov. (black squares).

FIGURE 9. The 14 types of Hypogeophis pti sp. nov., showing head and collars in dorsal and right lateral views. All specimen numbers with “ BMNH 2005. ” prefix: (a) 1834, (b) 1831, (c) 1828, (d) 1833, (e) 1836, (f) 1830, (g) 1826, (h) 1838, (i) 1825, the holotype, (j) 1832, (k) 1829, (l) 1827, (m) 1835, (n) 1837. Specimens in (a) – (f) male; (g) – (k) female. Scale bars 2 mm.

FIGURE 10. Twelve of the 13 paratypes of Hypogeophis pti sp. nov., showing posteriormost part of body in ventral view (the posterior end of the body is missing in the remaining paratype). All specimen numbers with “ BMNH 2005. ” prefix: (a) 1834, (b) 1831, (c) 1828, (d) 1833, (e) 1836, (f) 1830, (g) 1826, (h) 1838, (i) 1829, (j) 1832, (k) 1837, (l) 1835. Specimens in (a) – (f) male; (g) – (j) female. Scale bars 2 mm.

FIGURE 11. Hypogeophis pti sp. nov., paratype specimens in life collected from Fond Peper, Praslin, 2014. Specimen on left is BMNH 2005.1830 or 1832; specimen on right is BMNH 2005.1833.