Ichthyophis griseivermis, Poyarkov & Skorinova & Bragin & Kolchanov & Gorin & Trofimets & Yuzefovich & Le & Nguyen & Skutschas, 2025

Poyarkov, Nikolay A., Skorinova, Dana D., Bragin, Andrey M., Kolchanov, Veniamin V., Gorin, Vladislav A., Trofimets, Alexey V., Yuzefovich, Alexander P., Le, Dac Xuan, Nguyen, Tan Van & Skutschas, Pavel P., 2025, Integrative taxonomy reveals a new unstriped Ichthyophis Fitzinger, 1826 from Vietnam and provides new data on diagnostic osteological traits for Asian tailed caecilians (Gymnophiona: Ichthyophiidae), Vertebrate Zoology 75, pp. 405-440 : 405-440

Ichthyophis griseivermis sp. nov.

Table 1; Figures 2 , 3 , 4 , 5 , 6 , 7 , 8, S 1 – S 16

Holotype.

ZMMU A-8208 (field tag NAP-15224), an adult female, from Xuan Lien National Park , Bat Mot Commune, Thanh Hoa Province, Vietnam ( elevation 800 m a. s. l.; geographic coordinates: 19.985°N, 104.974°E), collected by A. P. Yuzefovich and A. M. Bragin from a bank of mountain stream on October 28, 2023 .

Paratype.

VRTC NAP 08953 (field tag NAP-08953), adult male, from Pu Hoat Nature Reserve , Tien Phong Commune, Nghe An Province, Vietnam (elevation 815 m a. s. l.; geographic coordinates: 19.755°N, 104.796°E), collected by N. A. Poyarkov from the bank of a river on May 15, 2019 .

Etymology.

The specific name “ griseivermis ” is a Latin noun in the nominative singular, given in apposition, derived from the Latin adjective “griseus” for “grey” and the Latin noun “vermis” for “worm.” The new species is named in reference to its characteristic uniform grey body coloration. The specific epithet also alludes to Grey Worm, the commander of the Unsullied, the warrior-eunuchs of Astapor with an unparalleled reputation for combat in George R. R. Martin’s fictional work “A Song of Ice and Fire” (also known as “Game of Thrones”). We suggest the following common names for the new species: “ Grey Worm Caecilian ” (in English), “? ch giun xám B? c Trung B? ” (in Vietnamese), and “Seryi rybozmey” (“ ????? ????????, ” in Russian).

Diagnosis.

The new species Ichthyophis griseivermis sp. nov. differs from other members of the genus Ichthyophis by the following combination of the morphological characters: unstriped body lacking lateral yellow stripe; adult total length 206–242 mm (based on two available specimens); snout blunt and rounded (snout length / head length ratio 0.06–0.08); tentacle aperture located closer to eye than to naris (tentacle aperture-naris distance / tentacle aperture-eye distance ratio 2.1–2.2); premaxillary and maxillary teeth 44–48, vomero-palatine teeth 43–48, dentary teeth 38, inner mandibular teeth 25–33; tail very short, acuminate, ending in a nipple-like cap; annuli angulate, total 301–306 (dorsal count), four interupted by cloacal disc, one posterior to cloacal disc, the degree of annuli angulation decreasing from head to cloaca with grooves appearing almost orthoplicate at mid-body and posteriorly; vertebrae 111–112; scales in one series per annulus (dosolaterally), present only in the posterior half of body.

Description of the holotype.

Adult female (Figs 6 – 8 ), specimen in a good state of preservation (Fig. S 15); a small oblique scar on the dorsal surface of body above the cloaca (Fig. 7 E, G ), small (< 15 mm) midventral longitudinal incision at midbody with some viscera protruding, including yellowish round mature ova (ca. 6 mm in diameter). Body subcylindrical; head, nuchal region, and trunk slightly dorsoventrally compressed. Body tapering posteriorly, more abruptly at about one-fifth of body length (Fig. 6 C – D ), ending in blunt tail tip, with a small nipple-like terminal cap (Fig. 7 E – H ). Tail downturned towards tip, very short ( TL / TAL ratio 85.5), slightly longer than tentacle-snout distance ( TAL / STTA ratio 0.68). Head longer than wide ( HW / HL ratio 0.70); head dorsal surface slightly flattened (Fig. 7 A – B ). Head somewhat more like V- than U-shaped in dorsal view (Fig. 7 C ). In dorsal view, head width at the level of mouth corner notably smaller than the width of the first collar ( HW / BW 1 ratio 0.92); head narrowing towards the tentacles and gradually tapering from the tentacles to the snout (Fig. 7 C ). In lateral view, head conically tapering on the distance between the first collar and nares (Fig. 7 A – B ). Nares located much closer to the tip of the snout than to eye ( ES / EN ratio 1.4; Fig. 4 A – B ). Lip margin flat and straight; corners of mouth notably closer to the throat than to top of head (Fig. 7 A – B ); mouth subterminal, with the upper and lower lips nearly identical in length ( SP / UJL ratio 0.10; Fig. 7 D ); in ventral view, gular region flat (Fig. 7 D ). Eyes very small ( ED / HL ratio 0.07), eye diameter slightly larger than that of naris and subequal to tentacle aperture; covered by grayish-white semitranslucent skin; eyes round, surrounded by narrow whitish ring, forming a dark-gray central disc, with a very small round pupil visible through the skin (Fig. 7 A – B ). In lateral view, eyes located almost equidistant from lip and top of head ( EL / ETH 0.91) (Fig. 7 A – B ). Tentacle apertures located over two times closer to eye than to naris ( EN / ET ratio 2.6; TN / ET ratio 2.2; Fig. 7 A – B ), almost reaching the edge of the upper lip; subequal in size to the eye (Fig. 7 A – B ). Tentacular papilli elevated above the adjacent skin and visible in dorsal, lateral, and ventral views (Fig. 7 A – D ). Naris small, oval with anterolateral orientation (Fig. 7 A – B ). Teeth small, notably recurved, almost hook-shaped, located in two rows on upper and lower jaws ( PMM 44, VP 43, DE 38, IM 25); outer mandibular tooth series approximately the same length as vomero-palatine tooth series. Tongue triangular with an acuminate tip, plicate posteriorly, lacking a distinct longitudinal medial groove; choanae narrow. The first collar slightly wider than the head at the mouth corner level ( HW / BW 1 ratio 0.92); the second collar gradually widens posteriorly; collar grooves widely incomplete dorsally, more distinct on the ventral surface (Fig. 7 D ) and on the sides (Fig. 7 A – B ); medially, anterior and posterior borders of collar region not well discernable, edged by the anteriormost body annuli (Fig. 7 C – D ); transverse nuchal grooves on dorsal surface of collar absent; in ventral view, second collar slightly longer than first ( C 1 / C 2 ratio 0.91); the anteriormost annuli complete in both ventral and dorsal aspects (Fig. 6 C – D ); body grooves encircle venter by forming an angle pointing towards tail, with the degree of angulation decreasing from head to cloaca: grooves distinctly angulated in the anterior one-third of body length (Fig. 6 D ) and appear almost orthoplicate at mid-body and posteriorly, with only a small medial portion of groove (ca. 0.5 mm in length) forming a shallow angle (Fig. 6 B ). Total number of annuli TAD 306, TAV 298 (dorsal and ventral counts, respectively); vertebrae 112. Cloacal slit longitudinal, located in an oval cloacal disc, interrupting four annuli on both sides (Fig. 7 H ). Tail bearing two annular grooves delimiting a single annulus and terminating in a distinct nipple-like terminal cap (Fig. 7 G – H ); scales in one series per annulus (in dorsolateral view), present only in the posterior half of body; scales oval in shape.

Coloration.

In life (Figs 6 – 8 ), body uniformly grey-brown; somewhat lighter on venter; with a slight pinkish-purple tint on lower flanks and belly (Fig. 8 ); annular grooves dark-grey, annuli greyish; margins of nares, lips, nares and tentacles whitish-beige; eyes dark-blue with a narrow whitish circle around. After 15 months in preservative (Fig. S 15), dark grey on dorsum and somewhat lighter ventrally; cloacal disc white; tail cap white; eyes, tentancles, and nares encircled by a narrow white margin.

Variation.

Variation in measurements and meristic characters of the type series is presented in Table 1. The paratype ( VRTC NAP 08953 , adult male) was found as a desiccated specimen and is in a moderate condition of preservation (Fig. S 16). Paratype body significantly dorsoventrally flattened; a large transverse incision present in the posterior one-third of the specimen length on the ventral side. The copulatory organ was extruded from the cloaca and damaged prior to specimen collection; the remains of the everted organ are visible on the ventral and lateral aspects of the specimen (Fig. S 16 A, B), but do not allow us to provide a description of its morphology. Overall, the male paratype VRTC NAP 08953 is generally very similar in most morphological traits to the holotype; however, it is c. 17 % longer than the holotypeis ( TL 242 mm), and has a slightly lower number of annuli ( TAD 301, TAV 292), one less vertebra ( VERT 111), and a greater number of teeth in all tooth series ( PMM 48; VP 48; DE 38; IM 33) all within the range of intraspecific variation expected for an Ichthyophis . It is identical to the holotype in in the number of annuli interrupted by the cloacal disc ( AV 4) and the number of annuli posterior to the cloacal disc ( TAT 1); and similar in body proportions. Due to desiccation and storage in ethanol for over five years, the original dark coloration of the paratype has significantly faded; the specimen is uniformly brown; the head and ventral surfaces are light-brown (Fig. S 16).

Comparisons (external morphology).

The new species lacks light lateral stripes, so it can be easily distinguished from all striped members of the genus Ichthyophis , and its comparisons with the unstriped congeners are the most pertinent. We will first compare Ichthyophis griseivermis sp. nov. with seven currently recognized unstriped species of the genus Ichthyophis from the Indochinese region (including Vietnam, Cambodia, Laos, and Thailand) and China; the main diagnostic characters separating the new species from these species are summarized in Table 1.

Ichthyophis griseivermis sp. nov. is a comparatively small-sized species ( TL 206.0–242.0 mm): though only two specimens of the new species are known to date and it is impossible to be confident about its maximal body size, the presence of mature ova in the holotype at least indicates that this specimen is adult at the TL of 206.0 mm. This can arguably distinguish the new species from its sister species I. yangi (endemic to Yunnan Province, China) ( TL 307.4–329.5 mm) and, with less confidence, from I. laosensis (known only from northern Laos) ( TL of the only known holotype 318.0 mm).

In body proportions, by the relatively longer eye-snout distance ( ES / HL ratio 0.46–0.48), the new species can be further distinguished from I. yangi , in which the snout is much shorter ( ES / HL ratio 0.33–0.39), and, though with less confidence, from I. acuminatus (distributed in northwestern Thailand and northwestern Laos) ( ES / HL ratio 0.40; however, this comparison should be taken with caution as its calculation is based on the ES measurement by Taylor 1960). At the same time, I. laosensis and, arguably, I. cardamomensis (endemic to the Cardamom Mountains, southwestern Cambodia) have a comparatively longer snout than the new species ( ES / HL ratios 0.58 and 0.51–0.60, respectively). Ichthyophis griseivermis sp. nov. has the tentacle aperture being situated comparatively farther from the eye ( TN / ET ratio 2.1–2.2) than in most other unstriped Indochinese Ichthyophis , including I. acuminatus ( TN / ET ratio 2.4–2.9), I. cardamomensis ( TN / ET ratio 2.8–3.2), I. catlocensis (endemic to Lam Dong Province of southern Vietnam) ( TN / ET ratio 4.5), I. laosensis ( TN / ET ratio 2.7), and I. youngorum (endemic to northwestern Thailand) ( TN / ET ratio 2.5). At the same time, in the new species, the tentacle aperture is situated comparatively closer to the eye than in I. yangi , where it is located almost in between the nostril and the eye ( TN / ET ratio: 1.1). Relative eye size is larger in the new species ( HL / ED ratio 14.5–15.5) than in I. chaloensis (endemic to Quang Binh Province, central Vietnam) ( HL / ED ratio 31.3) and, arguably, in I. acuminatus ( HL / ED ratio 20.9; however, this comparison should be taken with caution as its calculation is based on the ED measurement by Taylor 1960), but is smaller than in I. laosensis ( HL / ED ratio 10.9) and generally smaller than in I. cardamomensis ( HL / ED ratio 11.5–13.2). Ichthyophis griseivermis sp. nov. has a relatively shorter distance between eye and lip ( EL / HL ratio 0.08) than in I. laosensis ( EL / HL ratio 0.16), but this distance is greater than in I. yangi ( EL / HL ratio 0.04–0.06). The new species has a relatively more projecting snout ( SP / HL ratio 0.06–0.08) than I. acuminatus ( SP / HL ratio 0.01–0.05) and I. youngorum ( SP / HL ratio 0.01), and a slightly more projecting snout than I. yangi ( SP / HL ratio 0.04–0.05), but a shorter snout projection than I. chaloensis ( SP / HL ratio 0.14). The new species has a comparatively shorter tail ( TL / TAL ratio 66.7–85.5) than I. chaloensis ( TL / TAL ratio 58.3). Ichthyophis griseivermis sp. nov. has a comparatively wider body ( TL / BW 2 ratio 21.1–21.6) than I. cardamomensis ( TL / BW 2 ratio 23.2–37.4), I. catlocensis ( TL / BW 2 ratio 25.8), and I. chaloensis ( TL / BW 2 ratio 28.4); though this character should be taken cautiously, as a significant variation in body width has been reported earlier for a larger sample size of I. glutinosus ( Nussbaum and Gans 1980) .

Differences between the new species and its congeners observed in meristic characters should be taken with caution due to a small sample size available for our examination. Nevertheless, I. griseivermis sp. nov. has notably fewer total annuli both in dorsal count ( TAD 301–306) and in ventral count ( TAV 292–298) than I. catlocensis ( TAD 342; TAV 340), I. chaloensis ( TAD 344; TAV 342), I. laosensis ( TAD 346; TAV 345), I. cardamomensis ( TAD 322–364; TAV 320–359), and I. yangi ( TAD 369–372; TAV 367–369). The new species has generally fewer annuli interrupted by the cloacal disc ( AV 4) than in I. acuminatus ( AV 5–7), I. youngorum ( AV 5–7), and I. yangi ( AV 6), slightly fewer annuli interrupted by the cloacal disc than I. catlocensis ( AV 5), and slightly more than I. chaloensis ( AV 3) and I. laosensis ( AV 3). By having only a single annulus posterior to the cloacal disc ( TAT 1), the new species is distinguished from I. acuminatus ( TAT 2–3), I. cardamomensis ( TAT 2–6), I. catlocensis ( TAT 5), I. chaloensis ( TAT 5), and I. youngorum ( TAT 4). The new species has a slightly higher number of labial premaxillary-maxillary teeth ( PMM 44–48) than I. acuminatus ( PMM 37–43), I. cardamomensis ( PMM 23–38), I. chaloensis ( PMM 37), I. laosensis ( PMM 33), and I. youngorum ( PMM 22–28), but fewer premaxillary-maxillary teeth than in I. yangi ( PMM 51–53). Ichthyophis griseivermis sp. nov. has slightly fewer vomero-palatine teeth ( VP 43–48) than I. catlocensis ( VP 51) and I. chaloensis ( VP 54), but more than in I. laosensis ( VP 36), I. cardamomensis ( VP 28–29), and I. youngorum ( VP 33–40; note that the lower value was obtained from a partially damaged specimen and may be erroneous). The new species has more dentary (labial) teeth ( DE 38) than I. catlocensis ( DE 27), I. chaloensis ( DE 26), and I. youngorum ( DE 28–29; note that these values were obtained from partially damaged specimens and may be erroneous), but fewer than I. yangi ( DE 48–49). At the same time, the new species has more inner mandibular teeth ( IM 25–33) than I. catlocensis (16), I. chaloensis ( IM 11), I. youngorum ( IM 18–19; note that these values were obtained from partially damaged specimens and may be erroneous), and I. cardamomensis ( IM 19–22). Ichthyophis griseivermis sp. nov. further differs from I. cardamomensis by fewer vertebrae (VERT 111–112 vs. 120).

Furthermore, I. griseivermis sp. nov. can be readily diagnosed from the following unstriped species of Ichthyophis which occur outside the Indochinese Region and southern China. In particular, the new species differs from I. lakimi (Sabah, Borneo) by having more premaxillary-maxillary (labial) teeth ( PMM 44–48 vs. 16–25) and by having more inner mandibular teeth ( IM 25–33 vs. 14) (though the tooth counts for I. lakimi reported by Nishikawa et al. 2012 appear to be much lower than are typically known for Ichthyophis and require a re-examination); from I. billitonensis Taylor, 1965 (Belitung Is., Indonesia) by having more inner mandibular teeth ( IM 25–33 vs. 2); and by having more annuli in dorsal count ( TAD 301–306 vs. 251–254); from I. dulitensis Taylor, 1960 ( Sarawak, Borneo) by the absence of scales in the anterior half of body (vs. present); by having more inner mandibular teeth ( IM 25–33 vs. 8); and by the absence of a light marking on the throat (vs. present); from I. glandulosus Taylor, 1923 ( Basilan Is., Philippines) by having more annuli in dorsal count ( TAD 301–306 vs. 273–286); and by a higher number of vertebrae (VERT 111–112 vs. 102); from I. javanicus Taylor, 1960 ( Java Is., Indonesia) by having less annuli both in dorsal count ( TAD 301–306 vs. 351), and in ventral count ( TAV 292–298 vs. 348); and fewer annuli posterior to the cloacal disc ( TAT 1 vs. 10); from I. larutensis (Peninsular Malaysia) by the presence of inner mandibular teeth (vs. absent); and by a slightly higher number of vertebrae (VERT 111–112 vs. 107); from I. mindanaoensis (Mindanao Is., Philippines) by having more inner mandibular teeth ( IM 25–33 vs. 16–22); from I. monochrous (Bleeker, 1858) (Borneo Is., Indonesia) by having more annuli in dorsal count ( TAD 301–306 vs. 247); by having more inner mandibular teeth ( IM 25–33 vs. 8); and by a greater number of vertebrae (VERT 111–112 vs. 103); from I. orthoplicatus ( Sri Lanka) by having fewer annuli posterior to the cloacal disc ( TAT 1 vs. 7); and by having slightly more inner mandibular teeth ( IM 25–33 vs. 18–20); from I. sikkimensis Taylor, 1960 (northeastern India) by having more annuli in dorsal count ( TAD 301–306 vs. 276–292); by a greater number of vertebrae (VERT 111–112 vs. 106–108); and by having slightly more inner mandibular teeth ( IM 25–33 vs. 18–20); from I. singaporensis Taylor, 1960 ( Singapore) by the absence of scales on the anterior half of body (vs. present); by having more annuli in dorsal count ( TAD 301–306 vs. 260–273); by having fewer annuli posterior to the cloacal disc ( TAT 1 vs. 7); and by having more inner mandibular teeth ( IM 25–33 vs. 6–10); from I. sumatranus Taylor, 1960 ( Sumatra Is., Indonesia) by the absence of scales on the anterior half of body (vs. present); and by having fewer annuli posterior to the cloacal disc ( TAT 1 vs. 7); from I. weberi Taylor, 1920 ( Palawan Is., Philippines) by the presence of inner mandibular teeth (vs. absent); and by having fewer both in dorsal count ( TAD 301–306 vs. 313–329), and in ventral count ( TAV 292–298 vs. 304–322).

Comparisons (cranial features).

Overall, the holotype specimen of I. griseivermis sp. nov. ( ZMMU A-8208 ; for detailed osteological description see above) is characterized by the following combination of cranial and dental characteristics: cranium more like V-shaped in the dorsal view; circumorbital present as a small bone, crescent-shaped and widely open ventrally; circumorbital and frontal not in contact; tentacular canal is open laterally and confluent with the orbital aperture; frontals in contact one another along about one-third of their lengths (i. e., short midline contact of frontals following Wilkinson et al. 2014); the posterior edge of vomer is situated slightly anteriorly to the center of the palate (at about 44–45 % of the cranium length); ventral edge of the posterior process of pterygoid is situated barely below the level of premaxillary-maxillary teeth; the anterior part of the parasphenoid portion of os basale is wide; occipital condyles are widely spaced in ventral view; retroarticular process of pseudoangular elongated, with its rounded posterior end oriented nearly dorsally; and teeth are moderately sized, with gently posteriorly curved tips.

Below, we compare the cranial features of I. griseivermis sp. nov. with the few congeners for which skull morphology reconstructions are available via MorphoSource or from previous publications: I. asplenius , I. kohtaoensis , I. tricolor , I. multicolor , I. nguyenorum , and I. supachaii (based on Wilkinson et al. 2014; McGrath-Blaser et al. 2025 and our data, see the Data Availability Statement below). Comparisons with I. sikkimensis are limited because only the dorsal aspect of the skull has been shown for this species ( Gower et al. 2017: fig. 2 A). Additionally, we examined skull descriptions and illustrations of I. beddomei , I. glutinosus , I. larutensis , I. mindanaoensis , I. nigroflavus , I. singaporensis , and I. weberi presented in Taylor (1969: figs 2–11). Table S 5 summarizes the comparative morphological data on skull morphology for the new species and 14 other members of the genus Ichthyophis .

The new species differs from all other Ichthyophis species examined in having a small, crescent-shaped circumorbital, lacking the ventral portion, and bordering only the upper posterior corner of the orbital aperture (vs. a larger circumorbital with a posterior ventral process). The smooth, gradually tapering retroarticular process with its posterior end oriented dorsally is also a characteristic feature of the new species. Additionally, the new species differs from I. asplenius , I. beddomei , I. glutinosus , I. kohtaoensis , I. larutensis , I. mindanaoensis , I. multicolor , I. nguyenorum , I. nigroflavus , I. singaporensis , I. supachaii , I. tricolor , and I. weberi , but resembles I. sikkimensis in having a weakly zygokrotaphic skull (vs. the stegokrotaphic or weakly stegokrotaphic condition of the skull). Furthermore, the new species differs from I. asplenius , I. kohtaoensis , I. tricolor , I. multicolor , I. nguyenorum , and I. supachaii in lacking the stapedial foramen (vs. present in all these species; for other species the structure of the stapes has not been described or illustrated).

Additionally, I. griseivermis sp. nov. further differs from I. kohtaoensis in having a more like V-shaped cranium in the dorsal view (vs. more like U-shaped), in having the posterior edge of the vomer situated slightly anteriorly to the center of the palate, about 44–45 % of the cranium length (vs. the vomer is situated around the center of the palate, about 50 % of the cranium length), and by the laterally expanded foramen magnum with widely spaced occipital condyles (vs. dorsoventrally expanded foramen magnum with closely positioned condyles). The new species further differs from I. tricolor in having a laterally open tentacular groove confluent with the orbital aperture (vs. a laterally closed tentacular groove not confluent with the orbital aperture), by having moderately sized teeth with gently posteriorly curved tips (vs. enlarged teeth with strongly curved tips), by the ventral edge of the posterior process of the pterygoid situated barely below the level of premaxillary-maxillary teeth (vs. far below the level of premaxillary-maxillary teeth), and by the absence of the contact between circumorbital and frontal (vs. present). The new species further differs from I. multicolor in having the posterior edge of the vomer situated slightly anteriorly to the center of the palate, about 44–45 % of the cranium length (vs. vomer situated around the center of palate, about 50 % of the cranium length), and in the absence of the contact between circumorbital and frontal (vs. present). The new species further differs from I. asplenius in having a more rounded tip of the snout (vs. more blunt), in more ventrally located nostrils in lateral view (vs. more dorsally), in having a laterally open tentacular canal confluent with the orbital aperture (vs. partly laterally closed tentacular canal not confluent with the orbital aperture), in rounded choanae (vs. subtriangular), and in the absence of the lateroventral process of the squamosal (vs. present). The new species further differs from I. nguyenorum in having widely spaced occipital condyles in ventral view (vs. almost confluent) and in a comparatively wider anterior part of the parasphenoid portion of os basale (vs. narrow). The new species further differs from I. supachaii in having widely spaced occipital condyles in ventral view (vs. almost confluent) and in having a laterally open tentacular groove confluent with the orbital aperture (vs. partly laterally closed tentacular groove not confluent with the orbital aperture). The new species differs from I. sikkimensis in having a longer contact between the frontal and prefrontal (vs. shorter, L-shaped contact). The new species further differs from I. beddomei in having a more like V-shaped cranium in the dorsal view (vs. more like U-shaped), in lacking the contact between frontal and circumrobital (vs. wide contact), in having oblique and narrow posterior edge of prefrontal in dorsal view (vs. transverse), and in having long anterior process of pterygoid (vs. short).

Ichthyophis griseivermis sp. nov. further differs from I. glutinosus in having a more like V-shaped cranium in the dorsal view (vs. more like U-shaped), in having rounded snout tip in dorsal aspect (vs. blunt), in having a laterally open tentacular groove confluent with the orbital aperture (vs. a laterally closed tentacular canal), in having palatine tooth series terminating at the level of the anterior border of the adductor chamber (vs. extends behind the level of the anterior border of the adductor chamber), in having widely spaced occipital condyles in ventral view (vs. closely positioned), in having shorter midline contact between frontals (vs. longer), and in having oblique and narrow posterior edge of prefrontal in dorsal view (vs. rounded). The new species further differs from I. larutensis in having rounded snout tip in dorsal aspect (vs. blunt), in having a laterally open tentacular groove confluent with the orbital aperture (vs. a laterally closed tentacular canal), in having palatine tooth series terminating at the level of the anterior border of the adductor chamber (vs. terminates anterior to the adductor chamber), in having widely spaced occipital condyles in ventral view (vs. closely positioned), in having shorter midline contact between frontals (vs. longer), and in having long anterior process of pterygoid (vs. short), and in a comparatively wider anterior part of the parasphenoid portion of os basale (vs. narrow tapering). The new species further differs from I. mindanaoensis in having a more like V-shaped cranium in the dorsal view (vs. more like U-shaped), in having rounded choanae in ventral view (vs. distinctly triangular), in having a laterally open tentacular groove confluent with the orbital aperture (vs. a laterally closed tentacular canal), in having shorter midline contact between frontals (vs. longer), and in a comparatively wider anterior part of the parasphenoid portion of os basale (vs. narrow tapering). The new species further differs from I. nigroflavus in having a more like V-shaped cranium in the dorsal view (vs. more like U-shaped), in having rounded choanae in ventral view (vs. anteroposteriorly elongated, oval), in having widely spaced occipital condyles in ventral view (vs. in contact), in having long anterior process of pterygoid (vs. short), and in a comparatively wider anterior part of the parasphenoid portion of os basale (vs. narrow tapering).

Ichthyophis griseivermis sp. nov. further differs from I. singaporensis in having a more like V-shaped cranium in the dorsal view (vs. more like U-shaped), in having rounded snout tip in dorsal aspect (vs. blunt), in having rounded choanae in ventral view (vs. subtriangular), in having a laterally open tentacular groove confluent with the orbital aperture (vs. a laterally closed tentacular canal), in having palatine tooth series terminating at the level of the anterior border of the adductor chamber (vs. extends behind the level of the anterior border of the adductor chamber), in having widely spaced occipital condyles in ventral view (vs. in contact), and in a comparatively wider anterior part of the parasphenoid portion of os basale (vs. narrow tapering). The new species further differs from I. weberi in having a more like V-shaped cranium in the dorsal view (vs. more like U-shaped), and in having long anterior process of pterygoid (vs. short).

Finally, a scan of the skull of the I. laosensis specimen from Laos ( NCSM 86611 ) is currently available on MorphoSource ( https://www.morphosource.org/concern/media/000059682); however, unfortunately, the comparison of the new species with this cranial reconstruction appears impossible, since it is likely that the specimen NCSM 86611 is a sub-adult individual with some of the skull elements unossified or not in the definitive condition.

Distribution and natural history notes.

Currently, I. griseivermis sp. nov. is known from two protected areas in northern Vietnam: from Xuan Lien NP in Thanh Hoa Province and Pu Hoat NR in Nghe An Province (Fig. 1 ). Though at present the new species can be considered as endemic to a narrow montane area in the western parts of Thanh Hoa and Nghe An provinces of Vietnam, its occurrence in the adjacent parts of Houaphanh Province of Laos is anticipated; both known localities are located just 3–5 km from the Vietnam-Laos national border. The possible occurrence of the new species in Ben En NP in Thanh Hoa Province and Pu Huong NR in Nghe An Province also cannot be excluded, and further field survey efforts are needed to clarify the extent of its distribution.

The type locality is at an elevation of 800 m asl. The holotype was found on the bank of a small forest stream with a stony bottom and steep clay bank (Fig. S 17). The surrounding secondary montane evergreen forest is severely damaged by regular logging, but some old trees remain, including Cunninghamia konishii Hayata ( Cupressaceae ), forming mixed polydominant forests with Symingtonia populnea (R. Br. ex Griff.) ( Hamamelidaceae ), Carallia suffruticosa Ridl. ( Rhizophoraceae ), Engelhardtia roxburghiana Wall ( Juglandaceae ), Guarea excelsa Kunth ( Meliaceae ), Castanopsis ferox (Rosb.) ( Fagaceae ), Michelia mediocris Dandy ( Magnoliaceae ), Pellionia radicans var. grande (Gagnep.) H. Schroter ( Urticaceae ), Ardisia quinquegona Blume ( Primulaceae ), Litsea acutivena Hayata and Litsea yunnanensis Y. C. Yang & P. H. Huang ( Lauraceae ), and Alniphyllum fortunei (Hemsley) Makino ( Styracaceae ). The undergrowth is well developed; soil is densely covered with grasses, sedges, and fern thickets. The holotype was found in a small ravine at the foothill of a low mountain range composed of clays and shales with a limestone base. The holotype was found at night (ca. 23: 00 h) while slowly crawling among the stones on the banks of a small mountain stream during a rain with an ambient air temperature around 19 ° C. The holotype was observed crawling along the unflooded part of the bank covered with silt and large pebbles about 30 cm from the water’s edge. The paratype male was found in the daytime (10: 00 h) as a dead, desiccated specimen on a sandy bank of a river among large stones at an elevation of ca. 815 m asl. The two localities are separated by a direct distance of 31 km.

Though we don’t have direct observations on the new species reproductive biology, we can assume that, like the other members of the genus Ichthyophis , I. griseivermis sp. nov. is oviparous with aquatic larvae, which is also supported by the large size of the eggs in the new species. Like all caecilians, the new species is carnivorous; however, we do not have specific information about its diet. Other species of amphibians recorded at the same habitat in the Xuan Lien NP and in Pu Hoat NR included: Boulenophrys palpebralespinosa (Bourret, 1937) , Leptobrachella eos (Ohler et al., 2011) , Ophryophryne pachyproctus Kou, 1985 , Xenophrys lancangica Lyu, Wang & Wang, 2023 ( Megophryidae ); Polypedates megacephalus Hallowell, 1861 ( Rhacophoridae ); Amolops tanfuilianae Sheridan et al., 2023 , Hylarana cubitalis (Smith, 1917) , Odorrana cf. chloronota (Günther, 1876) ( Ranidae ); Quasipaa ohlera e Pham et al., 2025, Limnonectes bannaensis Ye et al., 2007 , Fejervarya limnocharis (Gravenhorst, 1829) ( Dicroglossidae ); and Tylototriton thaiorum Poyarkov, Nguyen & Arkhipov, 2021 ( Salamandridae ).

Conservation status.

At the present moment, the habitat of the new species at the type locality in Xuan Lien NP is subject to serious anthropogenic pressure. The lowland areas at the foot of the ridges and hills are subjected to overgrazing of cattle, buffalos, and pigs, which destroy the leaf litter and upper layers of soil; pigs also dig up the banks of rivers and streams. In the forested areas along the rivers and in the valleys between the ridges, small mammals, birds, reptiles, and amphibians are actively hunted by locals. Forests at the foot of the mountain are being cut down for firewood; the open territories are subsequently adapted for planting vegetables, establishing paddy fields, or pastures. Xuan Lien NP was established as a protected area in part to protect the last remaining groves of Fokienia hodginsii (Dunn) A. Henry & H. H. Thomas ( Cupressaceae ), also known as “ Po Mu, ” a precious species of timber because of its characteristic aroma and its exceptional density. Despite the protective measures to preserve F. hodginsii and tourist routes to the most impressive old trees, during our surveys we have repeatedly observed illegal logging and transportation of F. hodginsii wood by the local population. These observations suggest that nature conservation measures in the Xuan Lien NP should be strengthened.

Given the information provided above, we suggest that I. griseivermis sp. nov., as with the majority of nominal caecilian species ( Gower and Wilkinson 2005), should be considered as Data Deficient ( DD) following the IUCN’s Red List categories (IUCN Standards and Petitions Committee 2019) pending additional information on its distribution extent and population status.

Figures

Figure 1. Distribution of the unstriped species of the genus Ichthyophis from Indochina and southern China. Symbols indicating Ichthyophis species are identical to those used in Figure 5; a dot in the center of a symbol indicates the type locality of a species. Localities: 1 Xuan Lien NP, Thanh Hoa Province, Vietnam; 2 Pu Hoat NR, Nghe An Province, Vietnam; 3 Maandi, Jinping County, Yunnan Province, China; 4 Cha Lo, Quang Binh Province, Vietnam; 5 Cat Loc, Cat Tien NP, Lam Dong Province, Vietnam; 6 Phnum Dalai, Phnom Samkos WS, Pursat Province, Cambodia; 7 Luang Prabang, the former French administrative centre of “ Haute Laos ” (following Geissler et al. 2015; but see the Discussion for the problem of the I. laosensis type locality); 8 Mae Wang, Chiang Mai Province, Thailand; 9 Muang Liep, Sayaboury Province, Laos; 10 Bhuping summer palace, Chiang Mai Province, Thailand; 11 Doi Ang Khang, Chiang Mai Province, Thailand.

Figure 2. General skull morphology of the holotype of Ichthyophis griseivermis sp. nov. (ZMMU A- 8208, adult female, 206 mm total length). 3 D reconstruction of the skull is shown with colored rendering in dorsal (A), ventral (B), anterior (C), posterior (D) and left lateral (E) views, and of the left lower jaw in labial (F) and lingual (G) views. Scale bar equals 3 mm. Abbreviations: bas – os basale; car – foramen for the carotid artery; ch – choana; corb – circumorbital; fm – foramen magnum; front – frontal; jf – jugular foramen; ltf – lower temporal fossa; mpc - mediopalatinal cavity; mxpal – maxillopalatine; nas – nasal; nos – nostrils; oc – occipital condyles; orb + tc – orbit and tentacular canal; par – parietal; pmx – premaxilla; psa – pseudoangular; prfr – prefrontal; psd – pseudodentary; pt – pterygoid; q – quadrate; smx – septomaxilla; sphen – sphenethmoid; st – stapes; sq – squamosal; utf – upper temporal fossa; vom – vomer; vf – vomeral foramen.

Figure 3. Braincase morphology of the holotype of Ichthyophis griseivermis sp. nov. (ZMMU A- 8208, adult female). 3 D reconstruction of the braincase is shown with colored rendering in dorsal (A), left lateral (B), and right medial (C) views, and of the isolated sphenethmoid in posterior (D) and anterior (E) views. Scale bar equals 1 mm. Abbreviations: Id – incisure for the dorsal branch of the olfactory nerve; Iv – foramen for the ventral branch of the olfactory nerve; II – incisure for the optic nerve; Vop – foramen for the deep ophthalmic branch of the trigeminal nerve; VII – foramen for the trunk of the facial nerve; VIIIa – foramen for the anterior branch of the auditory nerve; VIImd – foramina for the medial branches of the auditory nerve; VIIIp – foramen for the posterior branch of the auditory nerve; bca – basicranial articulation; car + VIIpal – foramen for the carotid artery and the palatal branch of the facial nerve; dmp – dorsomedial process of the sphenethmoid; dv? – incisure for the dorsal vein; fe – endolymphatic foramen; fper – perilymphatic foramen; fv – fenestra vestibuli; jf – jugular foramen; ns – nasal septum; sn – sola nasi (processus conchoides).

Figure 4. 3 D reconstruction of the atlas of the holotype of Ichthyophis griseivermis sp. nov. (ZMMU A- 8208, adult female) in anterior (A), posterior (B), left lateral (C), dorsal (D), ventral (E), and right lateral (F) views. Scale bar equals 1 mm. Abbreviations: acot – anterior cotyles; mo – medial outgrowth; na – neural arch; pcot – posterior condyle; pzp – postzygopophyseal processes; scs – spinal cord support; snf – spinal nerve foramen.

Figure 5. Maximum Likelihood (ML) phylogenetic tree of the genus Ichthyophis derived from the analysis of 3967 bp of cyt b, 12 S rRNA, and 16 S rRNA mtDNA gene sequences. For voucher specimen information and GenBank accession numbers, see Table S 2. Numbers at the nodes correspond to ML UFBS / BI PP support values, respectively. Species symbols and locality numbers correspond to those provided on the map in Figure 1. Unstriped species of Ichthyophiidae are shaded in grey. The thumbnail shows the holotype of Ichthyophis griseivermis sp. nov. in life (ZMMU A- 8208; denoted by an asterisk in the tree); photograph by A. M. Bragin.

Figure 6. The holotype of Ichthyophis griseivermis sp. nov. in life (ZMMU A- 8208, adult female). A Dorsal view of annuli in the middle of the body; B ventral view of annuli in the middle of the body; C general dorsolateral view of the body, right side; D general ventrolateral view of the body, right side. Scale bar equals 5 mm. Photographs by A. M. Bragin.

Figure 7. Details of external morphology of the holotype of Ichthyophis griseivermis sp. nov. in life (ZMMU A- 8208, adult female). A Lateral view of the head, right side; B lateral view of the head, right side; C dorsal view of the head; D ventral view of the head; E lateral view of the tail, left side; F lateral view of the tail, right side; G dorsal view of the tail; H ventral view of the tail. Scale bar equals 5 mm (all photographs shown in one scale). Photographs by A. M. Bragin.

Figure 8. The holotype of Ichthyophis griseivermis sp. nov. in life in situ (ZMMU A- 8208, adult female). Photograph by A. M. Bragin.