CHAPTER III 



Hydroids ( at left ) and jellyfish 



Hydioicls, Jellyfishes, Sea Anemones, 



and Corals 



R 



/ADIALLY symmetrical, often gorgeously col- 

 ored, and festooned with one or more circlets of 

 graceful tentacles, coelenterates are indeed the "flow- 

 ers of the animal kingdom," but they are animals 

 nevertheless, and carnivorous at that. Their elegant 

 symmetry is an eflfective design for snaring prey from 

 any direction and passing it on to a centrally placed 

 mouth. 



Fleshy sea anemones hang tentacles downward 

 in rocky grottoes or hold their delicate petaled disks 

 upright in tide pools or on shaded rocks. Their coral 

 allies rise, like minute anemones, from rigid cups of 

 limestone, either singly or in massive colonies that in 

 tropical waters form huge reefs. Feathery sprays of 

 delicately colored hydroids soften rocky crevices and 

 tide pools or are seen as bedraggled brown plumes in 

 the beach flotsam. 



In warm temperate waters the sea floor below 

 low-tide mark is a colorful garden of foot-high sea 

 fans, sea whips, and sea feathers, displaying plume- 

 like or latticed branches of vivid reds, pinks, yel- 

 lows, and purples. Soft corals thrust up spongy lobes 

 like ghostly hands, and a little farther out the lovely 

 sea pens anchor by their fleshy quills in the sand or 

 mud. The deeper waters are a fairyland of tall and 

 flexible gorgonians that sway with the currents. 

 Through every opening and into every crevice of 

 these coelenterate thickets dart fishes and inverte- 

 brates of all kinds, seeking food and taking shelter 

 as do the animals in our woods. In the water above, 

 jellyfishes pulse gently about or drift with the cur- 



(Phyhnn Coeloitcrala or Cnidarici\ 



rents as minute little saucers or frighteningly large 

 bowls of jelly. 



At night the sea is lighted with new splendor by 

 the many coelenterates that luminesce when stimu- 

 lated. Millions of small jellyfishes flash with every 

 wave, making the dark water sparkle. Now the sub- 

 marine gardens reveal themselves as softly lighted, 

 scintillating pathways that fade and then sparkle 

 anew as the sea pens and other sessile coelenterates 

 react to the touch of wandering fishes and bottom 

 creatures. 



Of more than nine thousand species of coelenter- 

 ates, only a few small members, all belonging to the 

 most primitive class, the Hydrozoa, have managed to 

 invade fresh waters. These include the little hydras 

 of ponds and streams, an uncommon hydroid, a tiny 

 parasite in the eggs of the sturgeon, and two small 

 jellyfishes that turn up sporadically. Some hydroids 

 and sea anemones penetrate into brackish waters, 

 where sea water is diluted by fresh, but the coelen- 

 terates as a group, and the reef corals in particular, 

 flourish only in fully marine habitats and are notice- 

 ably absent near the mouths of rivers. 



The great banks of reef-forming corals, and the 

 luxuriant growth of other coelenterates that live on 

 these reefs, are not found outside the tropics and 

 subtropics. Yet many coelenterates, and even cer- 

 tain kinds of tall branching corals, are so abundant 

 in temperate and cold waters that one can hardly 

 think of this as a warm-water phylum. 



Beyond the depths to which the aqualung or div- 



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