Freshwater Macroinvertebrates in Hong Kong

Torleya arenosa

General appearance
Body color dark brown; size small medium up to 5mm long (excluding antennae & cerci)
A robust impression given by expanded mesonotum, enlarged femora & widened abdomen; covered by numerous hairs

Head
The details for mouthparts illustrated in the following pictures

Thorax
Thorax yellowish brown with numerous dark brown marks
All legs robost covered by dense hairs, a whorl of long setae across forefemora dorso-submedially
Distinct half of tarsi darken proximally

Abdomen
Abdominal segments IV - IX with postero-lateral projection
Terga yellowish brown with a pair of purplish brown spots and dark smear on terga I - IX, but absent on tergum V (looks paler)
Gills III - VII -- gill III operculate, largest covering parts of succeeding gills
Three caudal filaments subequal in length, but less than half of body length; whorls of setae present at each segment of filaments

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 from Bride's Pool, Sha Lo Tung, Wang Shan Keuk, Tai Tso Stream (Tai Mo Shan), Shing Mun, Ng Uk (Tan Shan River), Tai Po Kau Forest Stream, Mui Tsz Lam, Tai Tsui Hang (Ma On Shan), Sam Tsuen, Shek Mun Kap and Sam A Shui Tsuen (Lantau Island).

Habitat: Larvae are found in shaded riffles associated with sand and gravel substrates in shallow and moderate to fast flowing streams.