Two new species of Macrobrachium Spence Bate (Decapoda: Palaemonidae) from Ayeyarwady River, Myanmar with a note on Macrobrachium lamarrei (H. Milne Edwards 1837)

Abstract

Two new species of the genus Macrobrachium Spence Bate have been described from near Mandalay of Ayeyarwady (Irrawaddy) River, Myanmar (22°2′37″N; 96°2′37″E). Macrobrachium univmandalay sp. nov. is closely related to Macrobrachium spinosum Cai & Ng, 2002 and Macrobrachium yui Holthuis, 1950 and is characterized by the presence of 10–12 dorsal teeth of which 3–4 post-orbital, first tooth at about 1/4th of anterior carapace; second chelate legs are dissimilar in size and shape in which carpus of major leg distinctly shorter than palm, cutting edges of fingers with 2 large and 2–3 smaller denticles at proximal part and without denticles on the distal half. Minor leg in which merus longer than carpus and palm, carpus shorter than palm as well as fingers and fingers without denticles in the cutting edges. M. spinosum and M. yui differ from this species in all these characters above.Macrobrachium ayeyarwadiense sp. nov. shows close affinity with Macrobrachium horstii de Man, 1892 and M. spinosum and can be easily separated on the basis of difference in characters of rostrum, position and arrangement of teeth on upper and lower margins, position of first dorsal tooth, distance between post-orbital edge and first dorsal tooth and its relation to rostrum length, length of antennular peduncle in relation to post-orbital carapace, shape and structure of 2nd cheliped, nature, size and arrangement of spines on outer and inner margins of ischium, merus, carpus, palm and fingers and nature of denticles on cutting edges of major and minor legs. The species can at once be identified on the absence of tubercles at distal half beyond larger denticles on fingers, convex nature of merus, carpus and disposition of spines on them, swollen palm and curved nature of movable finger and crossed nature of fingers distally of major 2nd peraeopod. Nature of long stiff setae on inner side of ischium, merus and carpus of major cheliped is characteristic to the species. Minor 2nd cheliped is also species specific in which the fingers are slender and curved so that a wide gap exists when closed. A note on Macrobrachium lamarrei (H. Milne Edwards 1937) is also given in the text.