C. thonglonyai resembles the Rhinopomatidae in some features of the nose, leading edge of the wing, absence of the calcars, inflated nasals and maxillaries, free premaxillae, and many aspects of the dentition. It differs from this family notably by the unspecialised nature of the nostrils, large unconnected ears, specialized tragus, modified and uniquely structured wing, absence of the tail, and structure of the scapula, humerus, radius, and pelvis (Hill &Smith, 1981).

Craseonycteris resembles bats of the family Emballonuridae by the structure of the nostrils and the presence of rostral swellings; to a limited extent the structure of the premaxillae is similar. The structure of the tragus, lack of a tail, absence of postorbital processes and elaborate basioccipital pits, the dentition, and organization of the shoulder joint distinguish C. thonglongyai from emballonurids (Hill & Smith, 1981).

It is unclear whether the Myanmar and Thai populations are reproductively isolated. In terms of echolocation, the calls of the Myanmar populations are clearly distinct, whereas morphologically they are similar to populations in Thailand.

Myanmar population may form a monophyletic clade. However, this needs to be confirmed through the collection of further material. A more detailed study involving microsatellites is also desirable because of the faster mutation rate of these genetic markers and because bi-parentally inherited nuclear markers have been shown to support an alternative phylogenetic relationship, which cannot be observed using only maternally inherited mitochondrial DNA (Roca et al., 2004).

C. thonglongyai constitutes the sole known representative of the Family Craseonycteridae. Typically, C. thonglongyai has a thickened snout with two clearly defined, crescent-shaped nostrils. The eyes are minute and appear to be concealed by hair. The ears are large with a well-developed tragus. The tail and calcar are absent but there is a well-defined, dark interfemoral membrane, which is also wide and this may reflect an adaptation to foraging at low level or amongst vegetation (Lekagul and McNeely, 1977). There is a large glandular swelling on the lower part of the throat (Bates & Harrison, 1997). Females are noted to have a single pair of pectoral and a single pair of pubic nipples. The pelage colour is a light buffy brown above, slightly paler below, although there are seemingly two colour phases: one displays brown to reddish brown upper parts; in the other, the upper parts are grey (Lekagul & McNeely, 1977). The skull is characteristically small but with a relatively bulbous braincase. The premaxillae are fused at the dorsal and ventral midline and ring the nasal aperture. There is a total of 28 teeth.

The upper incisors are large and possess a strong cingulum at the base; they are separated from the canine by a wide diastema. The lower incisors, which are roughly equal in size, are long, narrow, and tricuspid, the central cusp being largest; between the canine and lower incisors there is a narrow diastema. The canines, which have a narrow cingulum, are long and slender; the upper canine has a small, prominent cusp on the inside edge, the same visible in frontal view; there are no accessory cusps present on the lower canine. The upper premolar is large, with a wide shelf on the inside and a prominent anterior cingulum cusp; the first lower premolar is large, longer than it is wide, and somewhat narrower and shorter than the second lower premolar. The molars have no special characters; the third is the smallest molar in both upper and lower dentition (Lekagul & McNeely, 1977).

Myanmar: Saddan-Sin Cave, Kayon Hill, 13 km. north-east of Mawlamyine (Moulmein), Mon State (Bates et al., 2001) and nine other sites adjacent to the Thanlwin and Ataran Rivers (Pereira et al., 2006)

Thailand: Sai Yok National Park, Kanchanaburi Province, western Thailand (Bates et al., 2001).

At Saddan-Sin Cave near Moulmein in Myanmar, a single specimen was collected at 6.25 p.m. on 11th. March in a 6 m. wide mist net extended over the upper of two exits. Despite two subsequent surveys on 14th. and 16th. March, no other individual was seen although echolocation calls thought to be those of C. thonglongyai were detected (Bates et al., 2001). Saddan-Sin Cave has an irregularly shaped roof structure and a number of Mega- and Microbats were observed roosting in different areas of the chamber. Craseonycteris was noted to leave the cave soon after sunset.

C. thonglongyai was found in Sai Yok National Park in Thailand only in small caves, far from the entrance in the most remote caverns, hanging high on the roof with individuals well separated from each other. Bats have been noted to take flight immediately on being disturbed. Individuals have been observed flying round the tops of bamboo clumps and teak trees, indicating that they may be foliage gleaners as well as taking small insects on the wing (Lekagul & McNeely, 1977).

Human disturbance has led to caves being abandoned by C. thonglongyai in Thailand (Hutson et al., 2001).