Eventually, I replaced it with a full-size tire, but I've always wondered why manufacturers say you shouldn't use the spare for longer than necessary. Since the spare tire is used so infrequently, carmakers have switched to narrow, compact spares to save space and weight. Of course, a spare tire is a lifesaver when regular tires go pop, but leaving the temporary tire on for longer than the manufacturer recommends invites a host of problems. First, a temporary spare isn't as durable as a normal tire.
Cells have become specialized and form true tissues and cnidarians are the first group to have B nerve cells organized into a nerve net B sense organs (statocysts and ocelli) B extracellular digestion Cnidarian Body Plan The diploblastic cnidarians are radially or biradially symmetrical with oral and aboral ends.
There are about 10, 000 species of Cnidarians. Cnidaria have no organs like hearts or lungs. They have an internal cavity used for respiration and a gastrovascular cavity (a stomach) with a mouth but they do not have an anus.They possess a body wall made from two layers (the ectoderm and the endoderm) separated by a jelly-like layer called the mesoglea.here are two major body forms among the Cnidaria-the polyp and the medusa. Sea anemones and corals have the polyp form, while jellyfish are typical medusae. When you look at them, you can see that these body forms are the same except that one is upside down.