Ixalus parvulus Boulenger 1893
Creators: name: Köhler, Gunther
name: Dost, Ole
name: Than, Ni Lar
name: Ohler, Annemarie
name: Charunrochana, Panupong Thammachoti
name: Chuaynkern, Yodchaiy
name: Chuaynkern, Chantip
name: Geiss, Katharina
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Amphibia
Anura
Rhacophoridae
Ixalus
Ixalus parvulus

description: Taxonomic identity of Ixalus parvulus Boulenger, 1893
We compared the lectotype of Ixalus parvulus Boulenger, 1893 (i.e., MSNG 29838; Fig. 2; Table 1) with all currently recognized species of Raorchestes from South-east Asia, partly based on data from literature. However, we were unable to confidently assign MSNG 29838 to any of the included taxa. Most notably, MSNG 29838 differs from all South-east Asian Raorchestes species by having distinctly shorter hind legs (ratio SHL / SVL 0.41 vs. 0.44–0.58 in the other taxa). Furthermore, its head is distinctly longer than wide whereas in most South-east Asian Raorchestes species the head is either broader than long or more or less as long as broad. Compared to other female adult Raorchestes, the body of MSNG 29838 appears much more elongate as opposed to the rather stout body of similar sized females of the examined South-east Asian Raorchestes species.
Finally, the tympanum is well visible in MSNG 29838 whereas it is much less distinct or even covered by skin in the majority of the examined South-east Asian Raorchestes. However, this probably is an artefact due to the long preservation time, which is likely because in the original description the tympanum is stated as hidden which we therefore accept as the original character state in the lectotype.
Of the Raorchestes species currently recognized from South-east Asia, five occur in the general geographic region of the type locality of Ixalus parvulus Boulenger, 1893 (i.e., Leiktho, Kayin State, Myanmar; see above): Raorchestes cangyuanensis, R. huanglianshan, R. longchuanensis, R. menglaensis, and our Clade R. sp. 2. Of these, we collected R. sp. 2 and R. longchuanensis at the type locality of I. parvulus. Of these five species, only R. menglaensis has a head that is longer than wide as it is in MSNG 29838 (vs. about as wide as long or wider than long in the other four spcies). Raorchestes huanglianshan differs from MSNG 29838 by having less toe webbing, a larger ratio IOD / EYD, and a generally darker body coloration. Raorchestes menglaensis differs from MSNG 29838 by having a smaller body size in adult females (SVL 23.6 mm vs. 18.9–22.2 mm; n=6). R. sp. 2 differs from MSNG 29838 by having a round inner metatarsal tubercle (vs. oval), and less toe webbing. Raorchestes cangyuanensis differs from MSNG 29838 by having more toe webbing and larger toe discs, especially on Toes I and II. Raorchestes hillisi differs from MSNG 29838 by having a distinct tympanum and a round inner metatarsal tubercle. Also, the only known adult female is just 17.5 mm SVL (vs. SVL 23.0 mm in MSNG 29838). Raorchestes malipoensis differs from MSNG 29838 by having a round inner metatarsal tubercle, a larger ratio IOD / EYD, and a smaller adult size (18.3–19.3 mm in adult females). Raorchestes rezakhani differs from MSNG 29838 in having an indistinct inner metatarsal tubercle, three dark bands on thigh and shank, and longer hind legs. R. sp. 1 differs from MSNG 29838 by having a round inner metatarsal tubercle (vs. oval), a head that is about as long as wide, and less toe webbing. R. sp. 2 differs from MSNG 29838 by having less toe webbing and a head that is about as long as wide.
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Among the other species from South-east Asia currently assigned to Raorchestes, R. gryllus can be excluded from consideration in respect of I. parvulus because it has a distinct calcar tubercle and a series of whitish tubercles along lower arm as well as on foot and tarsus unlike any of the other Raorchestes species in South-east Asia. Poyarkov et al. (2021) have proposed to transfer this taxon to Kurixalus.
Based on its original description, Philautus tytthus Smith, 1940 is similar in external morphology and color pattern to R. dulongensis and its type locality is just about 110 km SSW of the type locality of the latter taxon. Both taxa differ from the parvulus lectotype by having a small tympanum (one-third diameter of eye) and by having longer hind legs that reach to beyond anterior margin of eye (vs. to posterior border of eye in MSNG 29838).
Raorchestes menglaensis agrees in external morphology with MSNG 29838, including shape and relative size of toe discs and in the extend of toe webbing. However, the parvulus lectotype has shorter hind legs and a more elongate body than any R. menglaensis we examined. In a linear discriminant function analysis (LDA) of females with the lectotype of parvulus coded as “undetermined”, it was plotted within the morphospace of R. menglaensis (Fig. 3). The LDA assigns the lectotype either to R. cangyuanensis with a posterior probability of 51.99% or to R. mengalensis with 42.83% (Table 2). Another LDA, of males, including four paralectotypes plotted two of them close to the morphospace of R. annandalii with a posterior probability of 87.40% and 93.80%, respectively, one close to R. cangyuanensis with 79.97%, and one to either R. cangyuanensis (44.01%) or R. sp. 2 (50.64%) (Fig. 4).
In conclusion, of the South-east Asian species of Raorchestes studied, the parvulus lectotype agrees best with R. menglaensis in external morphology, but it does not appear to be a perfect match. Therefore, we refrain from formally synonymizing the two taxa awaiting further study, possibly including DNA sequence data from the parvulus lectotype.
Ixalus parvulus
— Myanmar: Kayin: “ District of the Karin Bia-po ” [= Leiktho]: MHNB 1246, NMW 16528, MNHN 1893.488, MSNG 29838, 50537.
description: Published as part of Köhler, Gunther, Dost, Ole, Than, Ni Lar, Ohler, Annemarie, Charunrochana, Panupong Thammachoti, Chuaynkern, Yodchaiy, Chuaynkern, Chantip & Geiss, Katharina, 2025, A taxonomic revision of the genus Raorchestes in Myanmar and Thailand with the description of two new species from Myanmar (Amphibia, Anura, Rhacophoridae), pp. 47-81 in Zootaxa 5613 (1) on pages 51-78, DOI: 10.11646/zootaxa.5613.1.2, http://zenodo.org/record/15216232