THE INVERTEBRATE LEGIONS 103 



Gorgonians are secondary reef builders and are largely tropical in distribution. 

 Several animals live in their bushy branches. Among these are the basket star, 

 Gorgoncephahis, hydroids, oysters, and some others. 



Dead man's fingers, Alcyonium, is representative of a group of anthozoans 

 called "soft corals." It is usuallv found in rather deep water, but it reaches up 

 to the low-tide mark. It has a flabby, mushroomlike texture supported by 

 calcareous spicules. Soft corals vary in shape from squat, spongy masses to erect, 

 treelike, branching forms and are found in all seas, but they tend to keep to 

 fairly deep water. 



The pennatulaceans include the very beautiful sea pansies, ReniUa, and sea 

 feathers, Pennatula. Both of these have a long single polyp that forms the axis 

 of the colony and which serves to anchor the colony in soft substratum. This 

 axis can move the colony slowly or withdraw the colony into the bottom when 

 it is disturbed. These are the most active of the anthozoans. On both sides 

 of the axis, there are extensions that carry the small feeding polyps. Most species 

 are beautiful shades of yellow, red, or purple and inhabit shallow, tropical, and 

 subtropical waters of all seas. Many of them are luminescent and will give off 

 light when disturbed. 



The anemones form a fairly compact group of anthozoans. They are devoid 

 of a skeleton and are noncolonial and flowerlike. Their distribution is world-wide 

 in all seas, and they are almost always found attached to hard, rocky, or coral 

 reef bottoms, where they sit waiting for prey to blunder into their tentacles. 

 The size range is from less than an inch to 2 feet in diameter. Anemones usually 

 avoid bright light and can move slowly on their bases more or less like a snail. 

 They like to attach themselves in crevices, with only the tentacles exposed. Their 

 colors are often extremely beautiful, ranging from bright green to white or dark 

 brown with delicate blues and reds. Anemones are able to contract greatly 

 in size, and when they do so the tentacles are drawn inside, which makes them 

 difficult to spot. (The common West Indian anemone is shown in a color 

 photogra'ph.^ Metridiuin is the most common temperate Atlantic species. The 

 west coast green anemone, Crihina, owes its color to the presence of zoochlorel- 

 lae. Adainsia (/tg. 38) is a remarkable anemone that lives in a mutualistic 

 relationship on the shells of hermit crabs, giving the crab protection by means 

 of its nematocysts and even patching holes in the shell the crab occupies 

 (Hyman, 1940). The anemone benefits by receiving food and transportation. 

 Several other anemones live in similar mutualistic svmbiosis with crabs. 



The true or madreporite corals are like small anemones but are colonial and 

 secrete calcium carbonate (lime) around their bodies for protection. (Their 

 environmental requirements are discussed in Ghapter 2 under coral reefs.) 

 Gorals are found north to temperate waters, but form reefs only in the tropics. 

 Star coral, Astrangia, is one that is found north to Cape God. Gorals show a 

 great variety in form. Some are small like star coral, some are massive like several 

 kinds of stone coral Qcolor photograph'), and the brain coral, Meandra Qfig. 31 

 and color photograph), some are stump-shaped like pedunculate corals Cf^g. 

 30), and some are branching like the staghorn coral, Acropora cervicornis 

 Cfig- 31), or the antler coral, Acropora palmata Ccolor photograph). There are 

 many species of small decorative corals. One is Eusmilia (fig. 30), an extremely 

 beautiful coral, which has large polyps even though the colonies are quite small. 



