Tenuibaetis peudofrequentus 

General appearance
Body size small, probably up to 4 mm long (excluding antennae & cerci)
Body spindle-shaped, head without a 'rigid' between antennae (found in Labiobaetis & Alainites)

Head
Antennae about 2 to 3 times as long as head width
Labium palp slender (cf. bat-like palp in Baetis illiesi or B. qiweiae)

Thorax
Hindwing pads present
Villiopore present
Nota brown to dark gray; mesonotum with several pale spots laterally & one w-shaped pale marking posteriorly

Abdomen
Gills I - VII, single & untracheated
Acute spines on posterior margin of terga
3-tailed, terminal filament about 0.6 times as cerci (cf. terminal filament minute giving an impression of 2-tailed in early stage)

 

Distribution:
In Hong Kong, specimens are recorded from Shing Mun, Tai Po Kau Forest Stream, Tong Min Tsuen & Pak Ngau Shek (Lam Tsuen River), Ma Po Mei Ysuen (nr. Lam Kam Road), Ha Wan Yiu, Tan Shan River, Tan Chuk Han, Ho Chung, Luk Keng Lam Uk (Nam Chung River) and Tai Shui Hang (Ma On Shan).

References:
Tong, X. & Dudgeon, D. (2000) Baetiella (Ephemeroptera, Baetidae) in Hong Kong, with descriptions of a new species. Entomological News 111: 143-148.
Kang, S.C., H.C. Chang & C.T. Yang (1994) A revision of the genus Baetis in Taiwan (Ephemeroptera, Baetidae). Journal of the Taiwan Museum 47(2): 9-44.

Remarks:
It was formerly known as Baetiella peudofrequentus.