ABSTRACT Aeginecta longicauda n. gen., n. sp. is described from material collected from a seasonally astatic aquatic habitat in Argentina. It is only known from the type locality and two male specimens; at this point the female remains unknown. Specific unique gonopod and genital segment features demonstrate that this taxon represents a unique genus within the Thamnocephalidae. Aeginecta n. gen most closely resembles Phallocryptus Biraben, 1951 and Thamnocephalus Packard, 1877. This new genus is easily diagnosed by the compound eye peduncle being extremely short, the frons and anterior surface of antennae II broadened laterally, with an intervening slit through which the compound eye may view the area forward on the animal, and the cercopods are as long as the abdomen. The gonopod proximal portion is bulbous with a transverse cleft, and projects ventrally from the segment. The gonopod distal eversible portion is minute, lamellar, and lies within proximal portion cleft. This is the fifth thamnocephalid genus reported from South America. The Neotropical region has the greatest thamnocephalid generic diversity in the world.

Abstract Dendrocephalus riograndensis n. sp., a new species of fairy shrimp, is described from a single temporary pool in Santa Vitória do Palmar, Rio Grande do Sul, Brazil. Males are readily separated from all other DendrocephalusDaday, 1908species by the form of the frontal appendage and the form of the first thoracopods. This new species is most similar to Dendrocephalus goiasensis Rabet & Thiéry, 1996 and could be confused with this species. This new species appears to be endemic to Rio Grande do Sul.