Starlet anemone (Nematostella vectensis)
N. vectensis genome facts: sequenced 2004-5; annotated 2006 475 million base pairs 27,000 genes Nematostella feeding series   ↓ general and genome resource links ↓

Nematostella vectensis, the starlet sea anemone, is a burrowing animal found in estuarine environments in the coastal U.K. and North America. Sea anemones belong to the phylum Cnidaria, a group characterized by a sac-like body plan with two germ layers (the ectoderm and the endoderm), radial symmetry and stinging cells called nematocytes. Nematostella is special among the cnidarians because is possesses swimming congregations of nematocytes called nematosomes, that are found throughout the gut and in the hollows of the tentacles and are delivered in the egg sacs to protect the developing embryos.

The Nematostella adult is a sedentary polyp that feeds on small zooplankton using its tentacles. Food enters the gut through the pharynx and is digested externally in the body cavity, which is lined by infoldings of the endoderm, the mesenteries. Male and female animals spawn to produce sperm and eggs. Upon fertilization, the zygote develops into a blastula that gastrulates by invagination and ingression and then results in a swimming larva called the planula. The planula then settles and transforms into a juvenile polyp. Unlike its more glamorous cousins, the jellyfish, anemones don’t have a swimming medusa stage in their life history.

Anemones and corals together make up the class Anthozoa that diverged away from other classes (Scyphozoa, Hydrozoa and Cubozoa) early in the evolution of the cnidarians. This position within the Cnidaria makes the study of anthozoans essential to understanding the common ancestor of cnidarians, and through that, the ancestor cnidarians share with all other true metazoans (all multicellular animals except for sponges).

Juvenile polyp, stained to show nuclei