National Geographic : 1961 Nov
National Geographic, November, 1961 And from Paul, thoughtfully: "Why are they green?" Lowering my hand into the aquarium, I brushed the tentacles of a bloom fully eight inches across. The green flower quivered but did not contract. The only sensation I felt was a slight stickiness. These creatures, I said, were coelenterates - members of the same animal phylum as the Portuguese man-of-war. Characteristic of the group is the presence of thousands of microscopic sting cells in the outer skin layer. Sting cells of the Portuguese man-of-war in ject a poison dangerous to man, but those of most anemones are harmful only to small marine animals, which comprise the main diet of the flowerlike creatures. Their green color, I explained, was due to tiny chlorophyll-laden algae living inside the anemone tissues. These specimens, com ing from a habitat of low light, were definitely less green than those I had seen in open, sun lit tidal pools. In shade-grown Anthopleura the internal algae are evidently less prolific, or produce less chlorophyll, than in those ex posed to direct sunlight.* Simple Intercom Transmits Stimuli Each of our captives now had its base glued to the floor of the aquarium, but meas urements made at hourly intervals would have revealed movement. Most anemones are capable of a slow, slow glide over the sur face to which they seem so securely fixed. *See the author's article, "How the Sun Gives Life to the Sea," NATIONAL GEOGRAPHIC, February, 1961. KODACHROMEBY PAUL A. ZAHL, NATIONALGEOGRAPHICSTAFF N.G.S.