mation of many coral reefs and are very abundant 

 in reefs of the western Atlantic. Another group of 

 hydrocorals, mostly of deeper hues of pink, red, vio- 

 let, or purple, also do best in warm waters but extend 

 into temperate seas as branching species in deep wa- 

 ter or encrusting ones in the more surfy shore waters. 

 A lavender or purple encrusting form, Allopora por- 

 phyra, occurs as calcareous patches encrusting rocks 

 at very low tide levels on the southern California 

 coast. Its white polyps may be glimpsed in the small 

 starlike craters that pock the surface of the massive 

 colony. 



THE SIPHONOPHORES 



The siphonophores are floating hydrozoan colo- 

 nies of great beauty, in which several kinds of polyp- 

 like individuals and a variety of medusa-like indi- 

 viduals are all combined into a single functioning 

 complex that swims or drifts its way about, dangling 

 drift nets of stinging tentacles to catch living prey. 

 Most common in tropical and semitropical waters, 

 they are to be found, especially in summer, drifting 

 even in polar seas. On the Danish cruises of 1908 to 

 1910, an hour's tow in the Atlantic or Mediterranean 

 brought in from six hundred to one thousand of these 

 delicately transparent, milky, or subtly shaded colo- 

 nies. Feeding polyps, contractile stinging tentacles, 

 reproductive individuals, swimming bells, floating 

 medusoids, protective flaps, and still other kinds of 

 coelenterate units share the food netted from the rich 

 animal plankton of surface waters. But many sipho- 

 nophores can release gas from their floats in rough 

 weather and sink below the surface, and some regu- 

 larly live at greater depths, down to nine thousand 

 feet. Even those at the surface are usually incon- 

 spicuous in the water and may escape notice despite 

 their occurrence in immense swarms brought together 

 by winds or currents. Around the globe, tropical and 

 semitropical waters have much the same component 

 of common siphonophores; those restricted to one 

 ocean are the exception. In all warm seas Hippopo- 

 diiis trails delicate strings of polyps from a small 

 cluster of swimming bells at the surface. A little more 

 compact is Physophora, also circumglobal in warm 

 waters but in summer carried northward by currents 

 to southern Greenland. Iceland, and the Barents Sea. 

 Superficially resembling little medusas are the tiny 

 blue or greenish disks of Porpita, which from the 

 deck of a liner in tropical waters can be seen by the 

 thousands, dotting the ocean for many miles. 



The only two siphonophores that are really well 

 known, however, are the usually sky-blue "by-the- 

 wind sailor," Velella (called the "purple sailor" in 

 areas where it tends to be violet ) , and the even more 

 vividly blue "Portuguese man-of-war," Physalia, 

 which may also be tinted with bright pink or orange. 

 In certain years both are carried northward in the 



Atlantic by steady winds and become stranded in 

 great numbers on British, Belgian, French, and 

 American Atlantic shores, far beyond their usual 

 range, where their novelty attracts much attention. 

 The same sort of thing happens in the southern hem- 

 isphere, Dakin says in Australian Seashores. There 

 Velella. Porpita, and Physalia are stranded on the 

 beaches of New South Wales, where the local name 

 for the last is "bluebottle." 



Velella looks like a single flat medusa, 1 to 3 

 inches long according to age or species, with a trans- 

 parent iridescent sail set diagonally across the long 

 axis of an oval float stiffened with horny material. 

 From beneath the transparent gas-filled float is sus- 

 pended the blue or pale purple body, with a single 

 large-mouthed feeding tube at its center and this sur- 

 rounded by rows of reproductive bodies and a circle 

 of stinging bodies that look like tentacles. Their sting 

 is innocuous to man. At intervals of several years 

 countless numbers are washed up on the beaches of 

 Florida, Oregon, California, Sicily, and many other 

 mild parts of the world. Fleets of Velella are accom- 

 panied and fed on by certain moUusks such as the 

 floating purple snail Janthina jaiithiiia. and by nudi- 

 branchs such as Fiona. Great shoals of Velella may 

 at times furnish the main food of the giant sunfish, 

 Mola mola, which is said to live entirely on floating 

 coelenterates. As Velella is swept northward along 

 the American Pacific coast, even sometimes to north- 

 ern Washington, the big fish follows, far beyond its 

 usual range. 



Physalia (Plate 8) occurs in middle latitudes in 

 the Atlantic, Pacific, and Indian oceans. For all the 

 blue and pink iridescent beauty of the gas-filled float, 

 the tentacles trailing downward for 40 to 60 feet, or 

 perhaps even as much as 100 feet, pack a sting that 

 can disable or kill a swimmer. Fatal injuries are said 

 to be due to allergic shock in people who have be- 

 come strongly sensitized by earlier experiences with 

 the proteins of the large stinging threads. Neverthe- 

 less, all swimmers in warm waters should give this 

 most dangerous of coelenterates a wide berth, and 

 even those who examine Physalia from a boat or 

 when the colony is stranded on a beach should use 

 care. So many may accumulate on beaches as to turn 

 the sand blue, and people suffer painful stings from 

 the dead tentacles in beach sand or on fishing gear. 

 We well remember the fiery welts on the arms of a 

 laboratory helper in Bermuda who cleaned an aquar- 

 ium that had housed a physalia weeks before and 

 apparently still contained tentacle fragments that 

 had dried on the walls. Oddly, there are animals that 

 can exploit Physalia without suffering harm. A small 

 fish, Nomeiis, has never been found except in the 

 company of Physalia, venturing away briefly, but al- 

 ways darting back to the safe harbor of the tenta- 

 cles so deadly to other fishes, even those as big as the 



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