The correct identification of species is an essential step before any study on biodiversity, ecology or genetics. Keratella is a genus with a predominantly temperate distribution and with several species being endemics or restricted geographically. Its diversity may be underestimated considering the confusing taxonomy of species complexes such as K. cochlearis. In this study, we examined genetic diversity and morphology among some Keratella populations from Mexico in order to determine if these populations represent different species. We analyzed a dataset of previously published and newly generated sequences of the mitochondrial COI gene and the nuclear ITS1 marker. We conducted phylogenetic analyses and applied three methods of species delimitation (ABGD, PTP and GMYC) to identify evolutionary significant units (ESUs) equivalent to species. Morphological analyses were conducted through scanning electron microscope (SEM) and morphometry under a compound microscope. In the present study, three new species Keratella cuitzeiensis sp. nov., Keratella huapanguensis sp. nov., and Keratella albertae sp. nov., are formally described. These species were collected in high-altitude water bodies located in the Central Plateau of Mexico. Combining DNA results through COI and ITS1 molecular markers and morphology it was possible to confirm the identity of the new species.

In this review, we include rotifers, copepods, and cladocerans, including other groups not usually deemed as zooplankters: i.e., protists, acari, and large branchiopods. The objectives of this study were to integrate the dispersed literature on the taxonomy and diversity of these freshwater zooplankton groups and to explain (1) how these contributions can be arranged in distinct historical periods and (2) how this knowledge has allowed the detection of exotic and threatened species. We divided the freshwater zooplankton studies in Mexico into three historical periods: the first one comprised the 1840s to the 1940s when foreign researchers carried out most studies during several expeditions. Spanish researchers promoted surveys on different zooplankton taxa at the end of this first period. The second period, from the early 1950s to the end of the 1990s of the XX century, showed a remarkably increased research activity in its last ten years only (that is, during the 1990s to 2000), represented by contributions of a new generation of Mexican zooplanktologists. This period yielded more complete zooplankton listings and detailed morphological descriptions of rotifers, cladocerans, copepods, and large branchiopods. The third period started from the year 2000 to date. During this time, listings and online faunistic baselines based on integrative taxonomy have been the primary trend. An account of exotic zooplankters and conservation issues of several native species are discussed. The results of this review show that the knowledge of the freshwater zooplankton of this country has increased significantly over the last 40 years, with at least 408 first records of species for Mexico. Currently, the knowledge of Mexican freshwater zooplankton is among the most complete in the world. However, it is estimated that only a small fraction of the true diversity has been documented.

Brachionus quadridentatus is a morphologically variable species distributed worldwide. Its taxonomy is confusing due the numerous infrasubspecific variants described in the taxon. Here we explore genetic diversity of certain B. quadridentatus populations, using sequences of COI mtDNA and 18S rDNA genes. With traditional morphology (taxonomic keys), the specimens identified fell into three recognized variants: B. quadridentatus quadridentatus, B. quadridentatus f. brevispinus and B. quadridentatus f. cluniorbicularis. The coalescent species delimitation analysis highly supports the presence of at least three putative species within B. quadridentatus complex in agreement with the phylogenetic result and GMYC analysis with the 18S gene. Nevertheless, the morphological and mitochondrial information show that the variation within each of the three putative species is much more extensive, finding seven monophyletic and highly divergent genetic groups (>10%) that have congruence with the morphotypes found in this study and ABGD analysis, which display clear morphological differences mainly in the diagnostic characters.

The littoral rotifer Lecane bulla is one of the most eurytopic members of the Lecane genus and is found in a wide variety of water bodies around the world. Taxonomic orthodoxy dictates that all specimens of this widespread taxon represent a single morphospecies. We analyzed a dataset of previously published and newly generated sequences of the mitochondrial COI gene of the L. bulla complex to examine cryptic diversity in the taxon. We undertook phylogenetic analyses and applied 3 methods of species delimitation (ABGD, PTP and GMYC) to identify cryptic species within L. bulla. Our results revealed the existence of 13 cryptic species based on the agreement of the different delimitationmethods. Genetic distances between the 13 cryptic species ranged from 4.6 to 16.8%. We found a barcoding gap where the intraspecific divergences (within cryptic species) were smaller than interspecific divergences (among cryptic species), thus supporting the 13 cryptic species delimited by the species delineation methods as independent entities. Our work reveals high levels of cryptic diversity in L. bulla and highlights the need to further studies to resolve the taxonomic status of these cryptic species (and genetic lineages).

Rotifer samples were obtained from 29 localities in northern Guatemala and central-southern Belize during March 2000 and June 2001. A total of 119 species were identified. Ten selected taxa are illustrated and commented: Euchlanis semicarinata, Lepadella apsicora, L. cryphaea, Lecane curvicornis f. lofuana, L. whitfordi, Monommata maculata, Scaridium bostjani, Trichocerca elongata f. braziliensis, and Z. hollaerti. The species Lepadella rhomboidula is a first record for the American Continent. The species are 71% cosmopolitan, 6 % tropicopolitan, and 4.2 % restricted to the subtropics. The Guatemala species number range was Petén-Itza lake (53 taxa), and Raxruja pool (three). La Democracia pool (49 taxa), and the Blue Hole sink-hole (six species) were the extremes in Belize. In total, 68 of the recorded taxa are new for Guatemala and 91 for Belize. Additionally, 47 species are registered by the first time in Central America. A comparison between these two countries and Mexico revealed that the south part of the latter conform a cluster with them, emphasizing the transitional character of this region between the Nearctics and the Neotropics. Furthermore, Guatemala and Belize have differences in species assemblages, as a response to the nature of their particular environments and topographical accidents.