马氏沼虾的成虾形态及特征鉴别

马氏沼虾是我国从斯里兰卡新引进的淡水虾类，外观略呈纺锤形，虾体共分为20节，除尾节外，虾体的每一节各具l对附肢，雌虾和雄虾在第五步足基部分别具有“A”和“M”状突起。头胸甲的胃区、心区、触角区表面较粗糙，两侧还有数条与虾体平行的浅棕色斑纹。虾苗时期多数个体呈淡褐色，性成熟后体色呈浅褐、淡青偏褐色或淡灰色。额角尖端微微上翘向前伸展，但不超出第二触角的触角片末端，上翘高度不超过额角上缘鸡冠状隆起的顶端，齿式为7～13／4～6。其生物学特性与罗氏沼虾和日本沼虾相比有许多相似之处，但在体色、额角、头胸甲和腹甲侧片等形态特征上差异十分明显。本文描述了马氏沼虾的外部形态及结构，比较了上述几种虾的主要特征，并就“雄虾特化”现象以第二步足与体长之比作为依据提出了质疑。

Morphology and character differentiations of adult prawn Macrobrachium malcolmsonii

Monsoon river prawn Macrobrachium malcolmsonii is an exotic freshwater prawn species recently introduced from Sri Lanka . The external appearance of the prawn is that of a spindle . The prawn consists of 20 pieces. Except telson , each piece has a pair of appendixes. Females and males have - shaped and Mshaped protuberances on the bases of f ifth walking legs. The surface of the gastric , cardiac and antennal areas of the carapace is rather coarse and there are several light brown mottles paralleled with prawn body on the both sides. During the fry ( 1- 3 cm) period, the body color of most individuals is light brown. Af ter sexually matured, the body color turns light brown, light blackish brown and light black. The tip of the rostrum slightly slants upward and extends forward, but neither going beyond the end of the antenna squama of the antenna seconda nor slanting higher than the tip of the coronal apophysis on the upper edge of the rostrum. The dental formula of rostrum is 7- 13/ 4- 6. Monsoon river prawn M. malcolmsonii belongs to the same genus as M. rosenbergii and M. nipponense. Though there are many similarit ies in their biological characteristics, there are also many differences in body color, rostrum, carapace and sternite pleurons, which can be obviously ident ified. This paper describes the external features and structures of M. malcolmsonii in detail, compares major characteristics of M. malcolmsonii and the other two species mentioned above. In addit ion, the questions are raised on the / male prawn specialization0 based on the second chelipod/ body length ratio.