Opinions and declarations Rendered by the International Commission on Zoological Nomenclature

The genus Hypergastromyzon is revised based on fresh topotypic specimens and two other locations in Borneo. Hypergastromyzon humilis is redescribed, along with descriptions of H. abditus, new species, from upper Katingan basin; and H. sambas, new species, from upper Sambas basin. A new genus, Engkaria, is erected to accommodate H. eubranchus. Engkaria differs from Hypergastromyzon in having very distinct sexual characters where males have heavy tuberculation over the opercle and modified pectoral-fin rays, the pelvic fins are not completely fused, and other characters. Engkaria eubranchus is redescribed based on a series of fresh specimens. An artificial key is provided for all species of Hypergastromyzon.

Opinions and declarations Rendered by the International Commission on Zoological Nomenclature

A freshwater mussel in the genus Hyriopsis Conrad, 1853 is described from the Chao Phraya Basin in central Thailand as Hyriopsis panhai, new species. This new species was once included in Hyriopsis bialata Simpson, 1900, but morphological investigations and multi-locus phylogeny based on concatenated data of COI, 16S, and 28S genes retrieved it as a distinct species, being separated from H. bialata 8.30% by uncorrected COI p-distance. The new species is conchologically similar to its sister H. bialata sensu stricto, but can be distinguished by being more laterally compressed in anterior portion; a more elongated and rounded posterior margin; and anterior adductor muscle scars that are distinctly separated from pedal retractor muscle scars.

Opinions and declarations Rendered by the International Commission on Zoological Nomenclature

Calamaria albiventer (Gray, 1835) is rediscovered at its type locality on Penang Hill on Penang Island, Malaysia after a six-decade absence of recorded sightings in the country. The species is known from only six locations in Peninsular Malaysia, Singapore, and Sumatra. A description of the new specimen is provided along with the first ever illustrations of the species in life and observations of its natural history. An updated taxonomic key to the Calamaria species of Peninsular Malaysia is included

Calamaria albiventer (Gray, 1835) is rediscovered at its type locality on Penang Hill on Penang Island, Malaysia after a six-decade absence of recorded sightings in the country. The species is known from only six locations in Peninsular Malaysia, Singapore, and Sumatra. A description of the new specimen is provided along with the first ever illustrations of the species in life and observations of its natural history. An updated taxonomic key to the Calamaria species of Peninsular Malaysia is included.

The primary purpose of this study is to successfully identify and characterise the tadpoles of Pelobatrachus stejnegeri in terms of colouration, external morphology, and oral disc morphology. In this study, a detailed description of the tadpoles through photographs and sketches is provided. Their different stages from stages 25 to 41 were also identified through a stereomicroscope. They were then photographed individually, and 20 different morphometric variables were measured using ImageJ software. The results showed that tadpoles of Pelobatrachus stejnegeri are small to medium in size and have an oblong and depressed body shape, dorsolateral eye position, round pupils which are oval in shape, and a dark brown line that runs to the eye. The vent tube is medial, having a pointed dorsal fin, and a relatively longer lower fin height than its upper fin. It also has an orange to brown pigmentation and possesses jade-like green speckles on the ventral body; after preservation, it eventually turns grey and the speckles are no longer present. The total length of the tadpole ranges from 28.19 to 37.14 mm from stages 25 to

41. The oral disc structure is umbelliform, with a bi-triangular to star-like shape, which it uses to filter food and attach to debris. This makes Pelobatrachus stejnegeri tadpoles unique among the tadpoles in the area. However, they are often overlooked because most studies only concern their adult stages. As only a few tadpoles in the country have been described, this study would still greatly contribute to tadpole research in the country

Recent studies of Rhacophorus reinwardtii in Southeast Asia split this species into five different species: R. norhayatiae, R. borneensis, R. kio, R. helenae, and R. reinwardtii. Meanwhile, the Sumatran Rhacophorus reinwardtii var. lateralis could not be ascribed to either R. norhayatiae or R. reinwardtii due to the poor condition of the specimen. Therefore, it was considered conspecific with R. norhayatiae. To identify the population of Norhayati’s Gliding Frog in Sumatra, we collected a specimen of R. cf. norhayatiae and three R. cf. reinwardtii and performed phylogenetic analyses using the 16S rRNA gene using Maximum Likelihood Analysis and Bayesian Inference. The results show that the specimen of Rhacophorus cf. norhayatiae from Sumatra is grouped with R. norhayatiae from Peninsular Malaysia and the Sumatran specimens of Rhacophorus cf. reinwardtii grouped with Javan R. reinwardtii. Based on morphology, we found that the Sumatran specimen of R. norhayatiae possessed the diagnostic features of R. reinwardtii var. lateralis. However, considering the presence of the senior homonym Rhacophorus lateralis Boulenger 1883, R. reinwardtii var. lateralis is here treated as a junior synonym of R. norhayatiae.