Caenis bicornis

General appearance
Body size small up to about 4mm long (excluding antennae & cerci)
Body densely covered with fine setae

Head
Antennal pedicles without long stout setae, only short fine setae if present
The details for mouthparts illustrated in the following pictures

Thorax
*Anterolateral corner of mesonotum with a distinct process
Fore fermora with a transverse row of 6-8 long stout setae on distal one-third place

Abdomen
Operculate gill II enlarged touching along midline to form a flap covering the posterior gills III - VII
Three caudal filaments subequal in length and about two-third of body length

Legs

 

Its mouthparts of labrum, mandibles, maxillae and labium are illustrated as follow (hypopharynx is excluded).

Labrum

Maxillae

Mandibles

Labium

 

Distribution:
In Hong Kong, specimens are recorded in Lam Tsuen River, Pokfulam, Tang Chuk Han, Ha Wun Yiu (Tai Po), Chuen Lung, Ng Uk (Tan Shan River), Ho Chung, Tai Mong Tsai, Ham Tin, Sha Kok Mei (Sai Kung), Wang Lung Hang and Shek Mun Kap (Lantau Island).

Habitat: Larvae are found in slow flowing current in streams.