Enigmas: keeping their secrets

Hermatobates singaporensis Cheng, 1976

The genus Hermatobates contains 12 species and is among the most elusive and rarely-encountered group of true bugs. For example, at the time when Hermatobates singaporensis was first described from Singapore in 1976, only three specimens were known. Members of the genus are found exclusively in marine habitats, usually on rocky shores and intertidal corals. They are sometimes known as “coral treaders”.

All species of Hermatobates are unable to fly, being completely wingless throughout their lives. At high tide, they hide in air pockets trapped in crevices or holes under boulders. Scientists also think that a layer of fine water-repelling hairs on their body surface may also help to trap air when they are submerged underwater.

At low tide they emerge, treading on the water surface to feed on small invertebrates. Apart from this scant information, their natural history remains a mystery. Hermatobates singaporensis is probably one of the rarest species in the genus and is found only in ASEAN and is so far only known from Singapore.

Banded Goby
Hemigobius mingi (Herre, 1936)

Most commonly found in mangroves, this fish is often found hovering almost upright above the bottom in small groups. In doing so, they appear very prominent against the bottom because of the silvery lines on their dark grey bodies. This display is unusual because many closely-related species are solitary in habit and remain close to the bottom, or otherwise attempt to appear less prominent. In most natural settings, to be prominent is to become someone else’s dinner. Scientists are still puzzled by this enigmatic behaviour. This species is restricted to ASEAN and is found in Brunei, Indonesia, Malaysia, Singapore and Thailand.

Bornean Flat-headed Frog
Barbourula kalimantanensis Iskandar, 1978

When this frog was first discovered in the Kapuas River (in Kalimantan, Borneo) in 1976, it was the first known species of the family from Borneo. In 2007, scientists were able to study this species in further detail. This led to the remarkable discovery that this frog has no lungs! Complete lunglessness is known only in amphibians and the Bornean Flat-headed Frog is the only known frog without a pair.

This species ‘breathes’ by drawing in oxygen directly through its skin from the cold, oxygen-rich streams in which it lives. Little else is known about its natural history. Furthermore, this species is only found in a small area in Kalimantan and is threatened by human activities that pollute the streams it lives in. This species is only known from ASEAN from Indonesia.

Enigmatic Saddle Oyster
Enigmonia aenigmatica (Holten, 1802)

A species overflowing with the enigmatic is the Enigmatic Saddle Oyster. Its common name and its scientific name (twice!) indicate that it is an enigma. Although recognised as a distinct species in 1802, it was only when animals were first observed alive that the truly remarkable nature of this species became apparent.

The two largest groups of molluscs are the snails (“gastropods”) and clams (“bivalves”). In general, snails crawl around and clams do not. The Enigmatic Saddle Oyster is clam-like but crawls around snail-like!

Charles M. Young made observations on living animals sent to him from Singapore in 1957. On placing the animals on glass slides, he was able to observe their movements from the other side of the glass.

This species can have both light- and dark-coloured forms, and the shell often grows to conform to the surface it is attached to. This has led to scientists naming some of these forms as distinct species. Outside of ASEAN, this species is found in Australia and China. Within ASEAN, it is found in Malaysia, the Philippines and Singapore.