No abstract

Resumen. Se estudiaron 13 localidades de las cuencas Copalita, Zimatán y Coyula, Oaxaca. En 4 muestreos se capturaron más de 3 200 crustáceos decápodos representando 3 familias, 4 géneros y 13 especies, y 3 posibles nuevas especies de los géneros Atya y Pseudothelphusa. Las especies se analizaron de acuerdo con su abundancia, frecuencia de aparición y distribución en las cuencas, y se comparó la composición de especies y distribución altitudinal de las localidades. La familia mejor representada fue Palaemonidae con 1 género y 8 especies, le siguieron Atyidae con 2 géneros y 3 especies y Pseudothelphusidae con 1 género y 3 especies. Potimirim glabra y Atya sp. 1 fueron las especies más abundantes; A. margaritacea y P. glabra las más frecuentes, pues se detectaron en 10 de 13 estaciones; Macrobrachium michoacanus se detectó en 9, y M. americanum y M. occidentale en 8 estaciones. Los juveniles de langostino tuvieron una alta frecuencia en 9 de las localidades. La riqueza y el índice de diversidad de especies se incrementaron hacia la porción baja de los ríos; en la porción alta, los valores fueron bajos y en la media de moderados a altos. Las localidades de muestreo se asociaron en 3 grupos de acuerdo con su altitud.

Lobithelphusa Rodriguez, 1982 is endemic to southern Mexico. Assigned to this monotypic genus is the freshwater pseudothelphusid crab, L. mexicana Rodriguez, 1982. The original description based on an old, dry, male specimen in the collections of the Natural History Museum, London, is brief and the crab was only partially figured. Lobithelphusa mexicana has subsequently never been recorded from Mexico and, consequently, the conservation status of this species is unknown. The type specimen has a complete, but detached left chela; is devoid of the left ambulatory pereiopods 1–3, with the fourth missing the carpus, propodus and dactylus; and its left first gonopod detached but retained in a glass tube kept adjacent to the crab. In spite of this damage the crab is still in remarkably good condition for a specimen registered in 1860. The purpose of this study is to apply computed tomography (CT) scanning techniques on the extant type, including its first gonopod, in order to provide detailed illustrations of the crab. These, in turn, shall be used to re-describe the species in order to help establish the current distribution status of L. mexicana in Mexico, and clarify its systematic position within the Pseudothelphusidae Ortmann, 1893.

ABSTRACT-The first formal report of Tertiary portunid crabs for Mexico is based on two new species, Portunus atecuicitli and Necronectes tajinensis, from the middle Miocene beds of the Tuxpan Pormation in Veracruz, east-central Mexico. Associated crustacean remains include fragments of calappid fingers, calappid carapace fragments possibly assignable to Matuta Pabricius, and callianassid hands. Low tolerance to osmotic variations of recent species of Portunus confirms paleoenvironmental interpretations for shallow, euryhaline, tropical waters during deposition of the Tuxpan Pormation.

A new species of Nebalia is described from Ría Lagartos in the Yucatán Peninsula, Mexico, increasing the number of described species in this genus to 13. The species closely resembles a complex of species recognized for the tropical western Atlantic that will need further study. The importance of the shape of the denticles on the dorsal plconal segments 6 and 7 as a taxonomical character is discussed.