Species: Rhithrogena siamensis  Braasch & Boonsoong, 2009
Classification
Phylum: Arthropoda
 Class: Insecta
  Order: Ephemeroptera
   Family: Heptageniidae
    Genus: Rhithrogena
Collection specimen
Holotype:
 - male in Museum für Naturkunde der Humboldt-Universität Berlin
Paratype:
     - males, females in Dietrich Braasch, Potsdam, Germany; 2 males, 2 females in Senckenberg Museum Frankfurt am Main, Ephemeroptera; 2 males, 1 female in Zoological Museum, Kasetsart University, Bangkok

Morphology:
Adult:
 Male of this species resembles that of Rhithrogena (Tumungula) unica Zhou & Peters, 2004 with hypertrophied foretarsal claw, basal tarsal segment roughly 1.4x longer than second, deeply excavated genital segment, styliger exhibiting remarkable projections and penis without titillators. In contrast to R. (T.) unica, the blunt part in the middle and hind claw is conspicuously longer than that in R. (T.) unica; the extended styliger projections of R. (T.) siamensis are not straight, but directed inwards, while the penis lobes are more elongated, being apically without reversed hook but having round gonopores (Braasch and Boonsoong, 2009).
Larva:
 Larva, differences are seen in mouthparts: labrum at outer rim without distinct medial emargination and dentate corners as in Rhithrogena (T.) unica; glossae are placed more distantly, leaning in laterad position; mandibles with outer incisor somewhat longer and narrower than in R. (T.) unica, inner incisor apically pointed; gill 1 differs in being pointed-crenulate and having longer plica more flatly rounded, whereas that of R. (T.) unica has a few unpointed crenulations and a shorter, more strongly rounded plica (Braasch and Boonsoong, 2009).


Figure


Larva of Rhithrogena siamensis (Source: Braasch and Boonsoong, 2009)
Habitat: Rhithrogena siamensis larvae cling to rock surfaces in medium- to fast-flowing water. Collections over most of the year revealed that the flight season at altitudes of 600 m was mainly during March/April, just before the beginning of the monsoon rains in May

Distribution:
 - Mae Hong Son province, Chiang Mai province, Chiang Rai province, Loei province

Work cited:
 - (1) Braasch, D. and Boonsoong, B. 2009. A new Notacanthurus Tshernova, 1974 and a new Rhithrogena Eaton, 1881 (subgenus Tumungula Zhou & Peters, 2004) from Thailand (Heptageniidae,Ephemeroptera). Zootaxa 2166: 33–44.
 - (2) Boonsoong, B. and Braasch, D. 2013. Heptageniidae (Insecta, Ephemeroptera) of Thailand. ZooKeys 272: 61–93.

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