SUBGENERIC DIFFERENCES IN HEAD SHIELD AND EPHIPPIA ULTRASTRUCTURE WITHIN THE GENUS BOSMINA BAIRD (CRUSTACEA, CLADOCERA)

Using S.E.M. techniques, we compared head pore and ephippia ultrastruc tures in 115 different populations of the four subgenera: Bosmina, Eub osmina, Neobosmina and Sinobosmina. We differentiated three types of h ead pores: median, lateral and frontal pores. The pattern of lateral p ores conforms to previously published descriptions. The frontal pore w ithin the subgenus Eubosmina is horseshoe-shaped, except in B. longisp ina and B. oriens, in which they are oval. In the subgenus Bosmina, th e frontal pore is oval with the longer axis perpendicular to the anima l plane of symmetry. Within the subgenera Neobosmina and Sinobosmina, the frontal pores are either circular or slightly oval. Ephippial surf ace sculpture does not differ noticeably among species within the genu s. In species with pronounced reticulation of the carapace, the same p attern appears on the ephippial surface. The function of the median an d frontal pores are unknown. The pores seem to be connected with the s upraoesophageal ganglion. The lateral pores are connected to a tissue of glandiform cells, and a narrow band or rope-like protrusion from th e pore is sometimes visible in preserved specimens.