several hours and then poked, a wave of soft bluish 

 light spreads over the whole surface of the colony 

 from the point touched. Renillas feed on small ani- 

 mals and larvae, stinging and swallowing them after 

 the prey has become entangled in a mucous net se- 

 creted over the surface. They are themselves known 

 to be eaten by nudibranch mollusks, one of the few 

 animal groups with a taste for the coelenterates. 



SEA ANEMONES AND CORALS 



(Subclass Zoantharia ) 

 This somewhat heterogeneous group includes the 

 sea anemones, solitary and without a skeleton; the 

 true or stony corals, with a skeleton and usually co- 

 lonial; the black corals; the zoanthids; and the "tube 

 anemones" or cerianthids. Not all fit the most com- 

 mon body pattern of parts repeated in multiples of 

 six; but none fits the neat alcyonarian model of just 

 eight feathery tentacles and eight internal partitions. 



THE SEA ANEMONES 



Though named for the Ipvely "windflowers" of 

 mountains and woodlands, the familiar anemones of 

 tide pools and rocky ledges more often suggest dahl- 

 ias and chrysanthemums. There are about a thou- 

 sand species of sea anemones, and most have a 

 broad, flat, rayed disk crowning the free end of a 

 stout muscular body. At the center of the rayed disk, 

 which gives the group its order name, Actiniaria, is 

 an elongate mouth, usually with a flagellated groove 

 at each end for directing a current of water to the in- 

 terior. Surrounding the mouth are one or more circles 

 of tapering hollow tentacles that belie their harmless, 

 petal-like appearance, wafting minute animals into 

 the mouth or cramming it with worms, crabs, and 

 fishes. 



The common colorings in temperate waters are 

 white, tan, salmon pink, orange, bro.vn, olive, or 

 green, but temperate-zone anemones may also be 

 vividly red or striped and dotted in contrasting and 

 breath-takingly beautiful geometric patterns of reds, 

 blues, grays, greens, and purples. Even in tropical 

 waters, where all groups put on a spectacular show, 

 the anemones distinguish themselves by their bril- 

 liance of color. 



Sea anemones unfold their disks in every sea, 

 growing larger and more numerous from the poles to 

 the equator, though any one species may not con- 

 form to the general trend. Mostly creatures of shore 

 and shallow waters, they extend to all depths. Un- 

 derwater photography has revealed an area 2100 

 feet deep, off the American Atlantic coast, where sea 

 anemones are the most abundant form of life. On 

 such mud bottoms they are anchored by a bulbous 

 base, attached to manganese nodules on the floor, or 

 cling to shrublike gorgonians or tall branching corals. 

 The Danish Galathea expedition hauled up a hith- 



erto unknown anemone from the Philippine trench, 

 about 30,000 feet down, and very appropriately 

 named it Galatheanthenmm. From 15,000 feet the 

 Galathea dredge yielded white anemones attached 

 to the long stalks of Hyalonema-like glass sponges. 



Entirely tropical are the floating minyads, many 

 of them a lovely blue color like that so often seen in 

 other floating coelenterates of warm surface waters. 

 The giant stichodacytyline anemones are also ex- 

 clusively tropical. These include Stoichactis, with a 

 disk up to 3 feet across, a full complement of plant- 

 like cells in its tissues, and an interesting set of small 

 crustacean and fish friends. Best known of its animal 

 commensals is the little pomacentrid "damsel fish," 

 Amphiprion, that darts among the tentacles of Stoi- 

 chactis in Indo-Pacific waters. Vividly banded in 

 black and orange, with fins edged in black and white. 

 it is very conspicuous as it plays about its anemone 

 host; and it is said to lure other fishes to the host's 

 disk or even to bring in offerings of food. At the least 

 threat the fish darts quickly to the safety of the wav- 

 ing tentacles. The fish is apparently immune to the 

 anemone's stings and perhaps becomes so by its 

 habit of mouthing and nibbling the tentacles. In any 

 case, a fish once acclimated to its host no longer in- 

 cites the discharge of stinging cells on contact with 

 the tentacles. Working at the Marineland of the Pa- 

 cific, an exhibition aquarium in California, and using 

 Stoichactis and Amphiprion imported from the Phil- 

 ippines, Davenport and Norris found that the protec- 

 tion of the fish seemed to reside in the mucous cover- 

 ing of its skin. The Dutch investigator Verwey, who 

 studied this anemone from Djakarta Bay, off Java, 

 has shown that at least in the conditions of an aquar- 

 ium, the big anemone does not flourish without its 

 small fish associate. Stoichactis is the upper limit of 

 the size range. At the other extreme are minute pol- 

 yps only a fraction of an inch long, some of them also 

 tropical, like Gonactinia prolijera of the eastern At- 

 lantic, which swims by waving its tentacles. 



In temperate waters few anemones are as wide- 

 spread as the plumose anemone. Metridiiim. which 

 lives mostly below low-tide mark. The soft, rounded, 

 feathery masses of tentacles, colored white, pink, 

 orange, or brown, decorate wharf pilings and the un- 

 derside of floating docks, or rise on broad muscular 

 bodies, usually of the same color, in rocky caves or 

 crevices where they can be seen at the very lowest 

 tides. The large lobed and frilled feeding disk, cov- 

 ered with many hundreds of tentacles and with very 

 little bare area around the mouth, is vaguely sugges- 

 tive of the many-petaled chrysanthemum (Plate 18). 

 Fine tentacles capture only minute plankton animals, 

 which are swept toward the mouth by beating cilia on 

 tentacles and disk. Metridittin extends pretty well 

 around the world in the northern hemisphere. It 

 flourishes in cool European waters, and on the Amer- 



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