Summary: Echinoids are another class of echinoderms. Echinoderms today are probably most familiar as starfish, but they also include sand dollars and sea urchins, and those groups are part of the class Echinoidea. Fossil echinoids are common in carbonate rocks from the Mississippian Period. The oldest known echinoids are from the late Ordovician. Most of the classes of echinoderms appear to have become established during the Ordovician, and many, including echinoids, have survived to the present. photo by Debivort via Wikipedia, under GFDLModern sea urchins have a globular body with five-fold symmetry, typical of all echinoderms, and a forest of spines encrusting the body. Fossil echinoids usually show only the body, often with a distinct 5-point star design on top. Ancient echinoids probably had spines as well, but they are not usually preserved intact with the body. Echinoids began to decline during the Pennsylvanian or late Carboniferous period, which we’ll cover next month, and by the Permian extinction there were only six species that we know about, and only two survived into the Triassic. But that was enough to give rise to the modern varieties of echinoids, which total about 950 species today. * * * On June 6, 1912 and for several days thereafter, Mt. Katmai in the Alaska Peninsula erupted. The series of eruptions devastated the area and created the landscape known today as the Valley of 10,000 Smokes, for the many steaming and smoking fumaroles and vents that were formed, including one large volcano called Novarupta. The summit of Mt. Katmai collapsed to make a caldera more than two miles across. The eruption was related to the subduction of the oceanic Pacific Plate beneath Alaska, and it was probably the largest volume of material erupted in the 20th century, at about 11 to 13 cubic kilometers, or about 3 cubic miles of ash and lava. That volume is about 30 times the volume erupted by Mt. St. Helens in 1980. The only other 20th century eruption that comes close was that of Mt. Pinatubo in the Philippines in 1991, which is also estimated at about 11 cubic kilometers of ejected material. Today, the Valley of 10,000 Smokes is part of the Katmai National Park and Preserve. —Richard I. Gibson photo by Debivort via Wikipedia, under GFDL
