Behningiidae and Potamanthidae (Insecta, Ephemeroptera) in Thailand Author Kwanboon, Sedtawut https://orcid.org/0000-0002-3858-9522 Animal Systematics and Ecology Speciality Research Unit (ASESRU), Department of Zoology, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand Author Sartori, Michel https://orcid.org/0000-0003-3397-3397 Museum of Zoology, Palais de Rumine, Place Riponne 6, CH- 1005 Lausanne, Switzerland & University of Lausanne (UNIL), Department of Ecology and Evolution, CH- 1015 Lausanne, Switzerland Author Boonsoong, Boonsatien https://orcid.org/0000-0002-8166-0021 Animal Systematics and Ecology Speciality Research Unit (ASESRU), Department of Zoology, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand fscibtb@ku.ac.th text ZooKeys 2021 2021-10-29 1067 57 82 http://dx.doi.org/10.3897/zookeys.1067.72779 journal article http://dx.doi.org/10.3897/zookeys.1067.72779 1313-2970-1067-57 8DB9C8FE9DF7438D92BA4B40E81F5DE1 921145FDEC60583E831A6266908B4BCD Rhoenanthus (Rhoenanthus) distafurcus Bae & McCafferty, 1991 Figures 10E , 11D , 14 , 15 Materials examined. 1 larva , Thailand , Kanchanaburi province , Sai Yok district , Pueng Wahn Resort , 14°12'08.9"N , 99°03'36.0"E , 15.X.2015 , B. Boonsoong leg ; 2 larvae , Ratchaburi province , Suan Phueng district , Pha Chi river , 13°30'57.3"N , 99°20'40.1"E , 19.IX.2016 , B. Boonsoong leg ; 1 larva , Nan province , Bo Kluea district , Sapan waterfall, 19°11'25.8"N , 101°11'56.3"E , 800 m , 28.XI.2020 , B. Boonsoong leg. Diagnosis. The larvae of Rhoennanthus distafurcus can be distinguished from those of other Rhoenanthus (Rhoenanthus) species based on the following characteristics: i) subapical spine of the mandibular tusk well developed laterally (Fig. 10E ), with a simple, short spine, ii) 16-20 medial rounded setae on mandibular tusk (Fig. 10E ) iii) length of the mandibular tusks ca 1.7-1.9 x length of head, iv) length of foretibiae ca 1.19-1.25 x length of the forefemora and about 2.5-2.8 x length of the foretarsi, (v) leg with colour marking as in Fig. 11D, and vi ) lack of bipectinated setae on the mandible ( Soldan T and Putz M 2000) . Distribution. Kanchanaburi, Ratchaburi, and Nan provinces. Remark. Bae and McCafferty (1991) described R. distafurcus based on imaginal specimens from Thailand, India, and Vietnam. The larva of R. distafurcus was described by Soldan T and Putz M (2000) based on specimens from Vietnam. In Thailand, a male adult of this species was found in Khao Yai National Park ( Bae and McCafferty 1991 ). In the present study, larval specimens of this species were found in western and northern Thailand.