TERMS OF USE This pdf is provided by Magnolia Press for private/research use. Commercial sale or deposition in a public library or website is prohibited. Accepted by S. De Grave: 14 Nov. 2009; published: 26 Feb. 2010 37 ZOOTAXA ISSN 1175-5326 (print edition) ISSN 1175-5334 (online edition) Copyright © 2010 · Magnolia Press Zootaxa 2372: 37–52 (2010) www.mapress.com/ zootaxa/ Article On two new genera of Asian prawns previously assigned to Macrobrachium (Crustacea: Decapoda: Caridea: Palaemonidae)* DAISY WOWOR 1 & PETER K. L. NG 2 1 Division of Zoology, Research Center for Biology, Indonesian Institute of Sciences (LIPI), Jalan Raya Jakarta Bogor Km 46, Cibinong 16911, Indonesia. E-mail: daisy_wowor@yahoo.com 2 Tropical Marine Science Institute and Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 119260, Republic of Singapore. E-mail: dbsngkl@nus.edu.sg * In: De Grave, S. & Fransen, C.H.J.M. (2010) Contributions to shrimp taxonomy. Zootaxa, 2372, 1–414. Abstract Two new genera of palaemonid prawns are described from South and Southeast Asia. The new genera are allied to Macrobrachium Bate, 1868, but can easily be separated by having a slender and glabrous second pereiopod, a long fifth pereiopod which is distinctly longer than the second pereiopod, a bilobed posterolateral margin of the fifth abdominal pleurite, the presence of one or two pairs of plumose setae at the ventroposterior margin of the telson, the absence of anterior lobes on male thoracic sternite 8 and distinctly larger adult females than males. Arachnochium gen. nov. (type species Palaemon mirabilis Kemp, 1917), can be distinguished from Tenuipedium gen. nov. (type species Macrobrachium palaemonoides Holthuis, 1950) by having a relatively shorter branchiostegal groove running from the base of the hepatic spine to the antennal carapace margin below the antennal spine, and having plumose setae which are longer than the inner pair of spines on the ventroposterior margin of the telson. Key words: Crustacea, Decapoda, Palaemonidae, Arachnochium, Tenuipedium, new genera, Asia Introduction When Kemp (1917) described Palaemon mirabilis from India, he stated that this species was quite different from typical members of the genus Palaemon by having a peculiar rostral form and extremely slender appendages, especially the fourth and the fifth pereipods which are unusually long. However, the presence of a hepatic spine made Kemp (1917) put the species in Palaemon. He was in doubt about the classification of his new species and believed that it was probably closer to Leander (presently known as Palaemon Weber, 1795) than to Palaemon (= present Macrobrachium Bate, 1868). Chace & Bruce (1993) agreed with Kemp (1917) and suggested that this species should be assigned to a new genus. The comparatively longer posteroventral branchiostegal suture behind and below the hepatic spine of Macrobrachium palaemonoides Holthuis, 1950, also led Chace & Bruce (1993) to consider that this species should be assigned to the genus Palaemon s. str., although the presence of a hepatic spine would exclude it. Chace & Bruce (1993) retained it in Macrobrachium with considerable reservation. For the present study, the available material of Palaemon mirabilis Kemp, 1917, and Macrobrachium palaemonoides Holthuis, 1950, has been re-examined and following Chace & Bruce (1993), two new genera are here established for these two species. Macrobrachium kulsiense Jayachandran, Lal Mohan & Raji, 2007, an Indian species allied to P. mirabilis , is also transferred to Arachnochium. Specimens examined are deposited in the Museum Zoologicum Bogoriense (MZB), Indonesian Institute of Sciences, Cibinong, Indonesia; the Zoological Reference Collection (ZRC) of the Raffles Museum of Biodiversity Research,