TULANE STUDIES IN ZOOLOGY AND BOTANY Volume 18, Number 3 March 16, 1973 THE SYSTEMATICS AND EVOLUTION OF THE GENUS CHIROSTOMA SWAINSON (PISCES, ATHERINIDAE; CLYDE D. BARBOUR 1 Department of Biology, University of Utah, Salt Lake City, Utah 84112 Abstract The genus Cliirostoma is composed of 18 species and six subspecies not including C. compressum, thought to be extinct. Except for a few populations of C. jordani near Durango City, Durango, it is restricted to the Mesa Central of Mexico where it makes up approximately 20 percent of the fish fauna. The following names in current usage are herein synonymized: Otalia = Cliiro-stoma; C. ocampoi, C. regani = C. hum-boldtianum; C. diazi = C. sphyraena; C. ocotlanae =: C. lucius. No subspecies of C. jordani are recognized. C. reseratum is recognized as a subspecies of C. consocium. The name C. attenuatum Meek is reapplied to the populations in Lakes Patzcuaro and Zirahuen currently designated as C. bar-toni. Five individuals from the lake at Balneario Cointzio, Michoacan are referred to C. charari De Buen. C. aculeatum is described as new. Chirostoma is divided into two species groups. The jordani group generally has high meristic values, the lateral line scales with canals, scales with laciniate margins and includes C. jordani, C. patzcuaro, C. chapalae, C. consocium, C. humholdtianum, C. estor, C. grandocule, C. lucius, C. sphy-raena and C. promelas. The arge species group generally has low meristic values, the lateral line scales with round pores (except for the last two species named below ) and scales with smooth margins and includes C. arge, C. melanoccus, C. charari, C. riojai, C. hartoni, C. attenuatum, C. laharcae and C. aculeatum. The similarity between C. arge and Me-laniris crystallina and the primitive nature 1 Present address: Division of Fishes, Mu-seum of Zoology, The University of Michigan, Ann Arbor, Michigan 48104. of C. jordani is noted. The evolution of Chirostoma is best explained by consider-ing the genus to be diphyletic; a Menidia-like ancestor of the jordani group invaded the Mesa Central first, followed at a later time by the Melaniris-like ancestor of the arge group. The evolution of the species is summarized in a hypothetical phylogenetic tree. Contents Introduction 98 Methods ... 98 Acknowledgments ... 99 Diagnostic Characters ... 100 Key to Species of the Genera Chirostoma AND Melaniris 101 The Jordani Group _ ... 102 Chirostoma jordani 102 Chirostoma patzcuaro ... 107 Chirostoma chapalae 107 Chirostoma humboldtianum 108 Chirostoma consocium consocium _ 110 Chirostoma consocuim reseratum _ 110 Chirostoma grandocule 112 Chirostoma compressum . 114 Chirostoma estor estor 114 Chirostoma estor copandaro .... 116 Chirostoma lucius 118 Chirostoma sphyraena 118 Chirostoma promelas 120 The Arge Group . ... 120 Chirostoma arge 122 Chirostoma melanoccus .... .... 122 Chirostoma riojai 122 Chirostoma charari 126 Editorial Committee for this Paper: Dr. Ernest A. Lachner, Curator, Division of Fishes, National Museum of Natural History, Washington, D. C. 20560 Dr. Robert R. Miller, Curator of Fishes, Museum of Zoology, The University of Michigan, Ann Arbor, Michigan 48104 97
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