Our long-running series of articles highlighting emerging model organisms continues in September with three entries, The Starlet Sea Anemone (Nematostella vectensis), Cephalochordates (Amphioxus or Lancelets) and The Western Clawed Frog (Xenopus tropicalis).

The slow rate of sequence evolution, the presumed high degree of preservation of ancestral traits, the ease of culturing, and the availability and experimental tractability of the early embryos have made Nematostella a prime cnidarian model for a number of biological studies. It serves not only as a model system for cnidarians, but also as an important representative of its phylum in comparisons with other lower Metazoa or Bilateria. Ulrich Technau and colleagues provide an overview of Nematostella, and protocols for spawning, in situ hybridization, antibody and phalloidin staining and BrdU labeling.

Cephalochordates, commonly called amphioxus or lancelets, are marine invertebrate chordates. Studies on cephalochordates have answered some long-standing questions concerning the evolution of vertebrates from their invertebrate ancestors and have also generated interesting avenues for further investigation of the evolutionary origin of developmental mechanisms that led to the emergence of the vertebrate body plan. Linda Holland and colleagues provide background on Cephalochordates, along with detailed methods for Amphioxus embryo collection, in situ hybridization, DNA extraction, and RNA extraction and extracting RNA from small amounts of tissue for RT-PCR.

Xenopus tropicalis is a small, wholly aquatic frog that is a diploid relative of Xenopus laevis. It shares many of the advantages of X. laevis as a model organism for studying aspects of vertebrate biology, particularly the genetic, biochemical, and environmental factors that influence vertebrate development from embryonic stages through adulthood. X. tropicalis is also finding uses as an important test species for assessing the impact of environmental toxins and disease on amphibians, which are in decline in many areas of the world due to water-borne pollutants and infectious agents such as the chytrid fungus. Frank Conlon and colleagues have contributed an overview of X. tropicalis, along with protocols for natural mating, in vitro fertilization, and tissue sampling and genomic DNA preparation.