Aurelia, or Moon Jellies, by the reefs off Lizard Island, Australia. Photo by Chris Meyer. Scyphozoans include most of the jellyfish familiar to beach-goers; other similar organisms are classified in the Hydrozoa and Cubozoa, two other groups of cnidarians. True jellyfish are graceful, and...
THE THEORY of evolution, formalized by Charles Darwin, is as much theory as is the theory of gravity, or the theory of relativity. Unlike theories of physics, biological theories (especially evolution) have been argued long and hard in...
Surely ever since the first fossils of obviously extinct animals were found, humankind has wondered: "Why did they die?" A poignant question, for it has relevance to us if extinct animals were wiped out by some catastrophe, couldn't that just as easily happen to us? Could we be found as fossils...
There are about 900 known species in the phylum Nemertini (also spelled Nemertina or Nemertea by different authors). Nemertines are known as "ribbon worms" because of the great length of many species; the European nemertine Lineus longissimus has been known to reach 30 meters (nearly 100 ft) in...
The Paleozoic is bracketed by two of the most important events in the history of animal life. At its beginning, multicelled animals underwent a dramatic "explosion" in diversity, and almost all living animal phyla appeared within a few millions of years. At the other end of the Paleozoic, the...
These animals, which are commonly called "peanut worms" because some have the general shape of shelled peanuts, are not particularly well studied. Only about 320 species have been formally described, all marine and mostly from shallow...
In 1900, a strange tube-dwelling worm was dredged from deep waters around Indonesia. While somewhat resembling tube-dwelling annelids, it lacked obvious segmentation; even more strangely, it also lacked a mouth, gut, or anus. This was the first discovery of the Pogonophora, an animal phylum...
The Urochordata, sometimes known as the Tunicata, are commonly known as "sea squirts." The body of an adult tunicate is quite simple, being essentially a sack with two siphons through which water enters and exits. Water is filtered inside the sack-shaped body. However, many tunicates have a larva...
The Phoronida is one of the smallest and least familiar phyla; there are about twelve or so living species in two genera, Phoronis and Phoronopsis. However, phoronids -- or "horseshoe worms," as they are sometimes called -- may be abundant in shallow marine sediments at certain localities....
In the early part of the Carboniferous, during the Mississippian Period, crustal plates were pulling apart in the northern Appalachian Mountains of eastern North America. This resulted in the formation of several basins separated by highlands. These basins filled with non-marine sediments that...