Not familiar creatures to most people, hemichordates form a small phylum (only a few hundred species). Their importance for the study of vertebrate evolution, however, cannot be underestimated. The fossil record of one group of...
Some species are colorless, but the vast majority are photosynthetic. As such, they are particularly important in lakes, where they may be the primary source of food for zooplankton. They are not considered truly autotrophic by some biologists because nearly all chrysophytes become facultatively...
The Ordovician period began approximately 490 million years ago, with the end of the Cambrian, and ended around 443 million years ago, with the beginning of the Silurian. At this time, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the...
Brachiopods are marine animals that, upon first glance, look like clams. They are actually quite different from clams in their anatomy, and they are not closely related to the molluscs. They are lophophorates, and so are related to the...
Most people are unaware of hornworts, though they are a quite common and widespread group of plants which may be found in tropical forests, along streamsides, and in disturbed fields around the world. Most species are small and unassuming greasy blue-green patches, but some tropical species can...
The period of Earth's history that began 2.5 billion years ago and ended 543 million years ago is known as the Proterozoic. Many of the most exciting events in the history of the Earth and of life occurred during the Proterozoic -- stable continents first appeared and began to accrete, a long...
diversity of form. The largest, Noctiluca, may be as large as 2 mm in diameter! Though not large by human standards, these creatures often have a big impact on the environment around them. Many are photosynthetic, manufacturing their own food using the energy from sunlight, and providing a food...
the Brachiopoda, is the outgroup on the above cladogram. Both groups belong to the larger group Lophophorata. Traditionally, the brachiopods have been split into two major groups, the Inarticulata and the Articulata. The Inarticulata got...
Ophiuroids are a large group (over 1600 species) of echinoderms that includes the brittle stars (Ophiurida) and basket stars (Euryalida). The more familiar Ophiurida, or brittle stars, usually have five arms and superficially resemble true starfish (Asteroidea). However, brittle stars have long...
classified together in a group variously known as the Aschelminthes, Nemathelminthes, and/or Pseudocoelomata. Today, these organisms are classified in about ten separate phyla. Nonetheless, it is sometimes useful to retain the name...