Discovered in July 2009 by Koichi Shibukawa, an expert working at the Nagao Natural Environment Fund (Japan) in the tributary canal of the Hau river of the Mekong river system in Cu Lao Dung district, Soc Trang province, Vietnam. Together with his colleagues at Can Tho University, Dr. Tran Dac Dinh and Master Tran Xuan Loi, all 3 published this new fish species in the journal Zootaxa No. 3363 (July 2012).

This fish has a special feature that males have gonads under the chin, just under the mouth, which looks like a pectoral fin. There is also a serrated saw and rod for grasping females. This species attains about 25 mm (0.98 in) in standard length and is translucent white. When mating, the heads of the female and the male will be placed close together, forming a 45-degree angle.

Phallostethus cuulong is the 22nd species in the family of cephalopods discovered.

According to Wikipedia.