And whereas jellyfish are radially symmetrical, like a flower, ctenophores are rotationally symmetrical, like a yin-yang symbol; their halves only match if you turn one a hundred and eighty degrees. Ctenophores collar their prey with glue-secreting cells called colloblasts that are unique to them.
And they are at their most innovative when it comes to the tiny beating hairs called cilia. We use cilia to clear mucus from our airways. Ctenophores use them as flippers, sense organs, and serrated teeth. One species, the sea walnut, uses its cilia to create imperceptibly subtle water currents that draw fish and other prey into its mouth. It is such an effective predator that, whenever it enters a new body of water, it throws the food webs into disarray. Haddock says that ctenophores are now becoming trendy, in part because they appear to be the sister group of all other animals—that is, the earliest clade to have branched off from the main trunk of animaldom, hundreds of millions of years ago.
For centuries, that honor had fallen to the sponges, but in Dunn, a Brown University biologist, compared genes from twenty-nine animals belonging to several phyla and concluded that ctenophores, not sponges, were the first to diverge. This revised tree, with ctenophores on the earliest branch, complicates several once tidy stories about the evolution of animal traits, notably the nervous system.
Sponges lack neurons entirely, but their genes seem to allow for chemical signalling of some kind. Ctenophores have nervous systems but lack the genes that other animals use to build neurons and neurotransmitters.
If sponges are the earlier of the two clades, the story unfolds neatly: they had the genetic building blocks for a nervous system, which ctenophores elaborated and bilaterians went to town on. But this narrative shatters if ctenophores branched off first. It could mean that they evolved nervous systems independently from all other animals, including us. Meanwhile, sponges either never developed true nerves or started off with nerves and lost them after all, what need does a sedentary filter feeder have for such an extravagance? This is a much tougher reality to accept.
The idea of one group of supposedly primitive animals going off-script and inventing a different nervous system, and then a second group actually losing theirs, is practically unconscionable. Read more in our special package on the lives of animals.
Recommended Stories. Philadelphia, PA: Elsevier; chap Rivlin K, Westhoff C. Family planning. Comprehensive Gynecology. Winikoff B, Grossman D. Goldman-Cecil Medicine. Philadelphia, PA: Elsevier Saunders; chap Updated by: John D. Editorial team.
Webster, N. All locations were coral reef habitat. Unless a woman is sure her partner is disease-free, condoms should be used in combination with the sponge. Figure 8. Author information Author notes These authors contributed equally: Daniel F. New York: Plenum.
Vaginal sponge and spermicides. Spermicides alone do not work very well.
About 15 pregnancies occur out of every women who correctly use this method alone over 1 year. If spermicides are not used correctly, the risk of pregnancy is more than 25 for every women each year.
Using spermicides along with other methods, such as male or female condoms or the diaphragm, will reduce the chance of pregnancy even more. Even by using a spermicide alone, however, you are still much less likely to become pregnant than if you did not use any birth control. How to use spermicide: Using your fingers or applicator, place the spermicide deep into the vagina 10 minutes before having sex. It reappeared in under new ownership, which spent millions to promote the brand before selling it to another company.
That new proprietor declared bankruptcy in late , taking the Today Sponge out of production last year. The new distributor hopes to bring some stability to the brand.
The birth control sponge (aka the contraceptive sponge or “the sponge” for short), is a small, round sponge made from soft, squishy plastic. The sponge covers your cervix and contains spermicide to help prevent pregnancy. The sponge prevents pregnancy two ways: It fits snugly. Using the birth control sponge correctly every time you have sex is important. Luckily, the sponge is easy to get the hang of — it’s similar to putting in a tampon. The birth control sponge starts working as soon as you activate the spermicide with water and put it in your vagina.
This summer, it is scheduled to also go on sale at 6, Walgreens stores. Compared with the birth control pill and condoms , the Today Sponge may generate comparatively little revenue.
It can have a failure rate of more than 10 percent. And it does not protect against sexually transmitted diseases. Mayer said. But he expects significantly decreased sales now. Another reason is that health experts who once thought the spermicide component inhibited sexually transmitted diseases now warn that the material may actually increase the risk of transmission, he said. View all New York Times newsletters. And whatever its business prospects in , the Today Sponge has a cultural status that transcends its role as a mere drugstore convenience.
Originally developed in the s, the Today Sponge was pulled off the market in after inspectors from the Food and Drug Administration found bacterial contamination at its manufacturing plant.