Occurrence of Tetrahedral Eggs in the Streptocephalidae Daday (Branchiopoda: Anostraca) With Descriptions of a New Subgenus, Parastreptocephalus, and a New Species, Streptocephalus ( Parastreptocephalus ) Zuluensis Brendonck and Hamer

Abstract

ABSTRACT Streptocephalus (Parastreptocephalus), new subgenus, comprises *Streptocephalus (Parastreptocephalus) sudanicus, S. (P.) lamellifer. S. (P.) kaokoensis, and S. (P.) zuluensis, new species, Brendonck and Hamer. These species all produce tetrahedral eggs, a unique feature within the family Streptocephalidae, and share a similar male antennal morphology, which differs from that in all other streptocephalids. The designated type species, S. (P.) sudanicus, is extensively redescribed. In addition, the differentiating characters for S. (P.) zuluensis are presented. Both species can be distinguished using features of the morphology of their resting eggs and of the male antennae. A key to the species is also provided. Egg morphology and male antennal morphology appear to be consistent taxonomic criteria for the proposed subgenus. The presence of taxon-related differences in egg morphology raises the question whether or not differently shaped eggs confer any selective advantage. We suggest that selective pressure on the amount of energy allocated to reproduction has resulted in the fact that eggs share a combination of characteristics (hatching response, dispersal ability, drought, and mechanical resistance), which allows them to endure a specific set of environmental conditions.