Versatile. 

 Powerful. 

 Durable. 

 Incredible. 



With over 50 EF lenses to choose from, here's 

 a closer look at three to use with Canon's 

 35mm full-frame D-SLRs. The large zoom 

 range of the EF 24-1 05mm f/4L IS USM 

 makes it one of our most versatile, easy- 

 to-use stanaard zoom lenses. And with 

 Image Stabilizer technology, camera shake 

 is corrected by up to three stops. Looking for 

 speed? Try the new EF 85mm f/1 .21 II USM 

 medium telephoto lens— perfect for portraits, 

 which uses a high-speed CPU to achieve 

 autofocus speed approximately 1.8x faster 

 than its predecessor. Or, if you really have to 

 see it all the EF 15mm f/2.8 Fisheye can 

 capture an incredible 1 80° angle of view, for 

 intriguing effects. 



Canon isn't just any camera, 

 so don't use just any lens. 



mageANYWARE 



©2006 Canon U.S.A., Inc. Canon is a registered trademark of Canon 

 Inc. in the United States and may also be a registered trademark 

 or trademark in other countries. IMAGEANYWARE is a trademark 

 ot Canon, All rights reserved. For more information, visit us at 

 www.canoneot.com or call 1-800-OK-CANON 



Is. 



THE NATURAL MOMENT 



See preceding two pages 



Hover over the maw 

 of a giant clam and 

 you'll be mesmerized by 

 the life between its 

 shells — far more stunning 

 than any bubbling mer- 

 maid. Intense, kaleido- 

 scopic colors are swirled 

 and stippled into patterns 

 that recall the adage about 

 snowflakes: no two are 

 ever alike. The colorful 

 sheath of tissue, appropri- 

 ately dubbed a mantle, 

 spans the two scalloped 

 shells that it accretes; the 

 shells of some species can 

 exceed four feet in length 

 and several hundred 

 pounds in heft. Truly, 

 they are the behemoths of 

 the bivalves. 



Giant clams (in the 

 subfamily Tridacninae) take years to 

 reach elephantine status, growing 

 throughout a lifetime that sometimes 

 lasts a century. The juvenile pictured 

 here measured only about eight 

 inches across. Photographer Paul 

 Sutherland spied the blue beauty in 

 shallow waters around Layang 

 Layang, an atoll ninety miles from 

 Borneo in the South China Sea. 

 Finding large specimens there or 

 anywhere else has become a chal- 

 lenge, because of overfishing and 

 shrinking habitats. 



Entranced, Sutherland zoomed in 

 on the muscular hole where the clam 

 spews out wastewater: a second anus, 

 you might say. Clams filter-feed by 

 siphoning in surrounding water, rak- 

 ing what they want through their gills, 

 and pumping out the leftovers. Given 

 the blimplike size of species such as 

 Tridacna gigas, which is the largest of 

 them all, the clams have the power to 

 siphon loads of water quickly — 

 enough to collect plenty of food 

 themselves. But, in the marine world, 

 extra bulk can offer valuable real estate 

 for ready profit. Giant clams lease 



their personal space and 

 increase their food con- 

 sumption by taking in 

 algae as tenant farmers. 

 The algae, known as 

 zooxanthellae, live by 

 the millions inside the 

 clams, where they actu- 

 ally provide most of the 

 clams' nutrients. 

 To produce energy for themselves 

 and for the clams, algae need intense 

 sunlight. So, as a precaution for the 

 clam, evolution has ensured that pig- 

 ments screen out ultraviolet rays — 

 which, it turns out, accounts for 

 much of the color variation on the 

 creature's fleshy surface. The clams 

 keep their end of the symbiotic bar- 

 gain by keeping a few "windows" 

 clear of pigment, finding a permanent 

 spot near the surface, and staying 

 open during daylight hours — all to let 

 in some light. (They can still exercise 

 ownership control on the algal popu- 

 lation, often digesting or expelling 

 any unwanted tenants.) But, because 

 the clams' only means of defense is 

 shutting themselves inside their tough 

 shells, staying open leaves the clams 

 vulnerable to attack. 



So, what tells them when to clam 

 up? Motion sensors, for one. Plus the 

 giant clams have eyes — hundreds of 

 rudimentary retinas that rim their 

 mantles. Sutherland was undoubtedly 

 spotted by the eyespots on his subject: 

 the clam winked shut several times as 

 he swam above it. — Erin Espelie 



6 NAT uk A I history June 2006 



