THE INVERTEBRATE LEGIONS 99 



The last of the hydrozoan groups is that of the Portuguese man-of-war, order 

 Siphonophora. These are not single animals as is commonly supposed, but are 

 floating colonies consisting of several kinds of medusas and polyps living together. 

 One medusa forms the bell or float of the colony. Other medusas form swimming 

 bells, which move the colony through the water. The polyp members of the 

 community contribute the feeding individuals, tasting or feeling individuals, 

 stinging individuals with nematocysts, and reproductive individuals. Thus, a 

 siphonophore is actually a complex colony of manv kinds of individuals all 

 specialized for diff^erent functions. Not all kinds of individuals may be present 

 in a colony. For instance, the Portuguese man-of-war, Physalia QColor Plate 10^, 

 lacks medusoid swimming bells and depends solely on the wind for distribution. 



All of these colonial siphonophores are pelagic. Most are small and delicate, 

 but the purple sail, Velella, and the Portuguese man-of-war are rather large. 

 Of these, the latter is famous for the power of its large nematocysts. Bad stings 

 can cause cramps, nausea, difficulty in breathing, or, very rarely, death. One of 

 the authors received the stings of only two nematocysts in his heel. In very 

 short time, the poison had traveled to the region of the groin, making walking 

 painful. Bad stings should receive immediate medical attention. The man-of-war 

 reaches a size of a foot across the float and with tentacles over 30 feet long. 

 It is thus able to catch a fish the size of a mackerel. 



True Jellyfishes: Class Scyphozoa — Figure 27 



This is a rather small, compact group of only two hundred species. No true 

 jellyfish has a velum as do the hydrozoan jellyfishes. Most have polyp generations 

 of small size, which produce medusas by a type of budding (strobilation) during 

 the warm months. 1 hese are the common, large medusas and are found in all 

 seas, particularly those of temperate and cold zones. They are common objects 

 cast up on beaches. (A typical species, Pelagia, is shown in Color Plate 10.) 



The true jellyfish common in warm or tropical seas are the cubomedusans, 

 which are named for the high, squarish or cuboidal shape of the bell. At each 

 corner of the bell is a single tentacle or group of tentacles. Caryhdea is a common 

 example. It is an inshore jellyfish, a strong swimmer, a fish-eater mainlv, and has 

 a strong sting. Most cubomedusans are only 1 to 2 inches across, but some reach 

 10 inches. Their sting has given them the name of "sea wasps." 



The discomedusans are the typical jellyfishes which are most common in 

 temperate and cold waters. They have round, hemispherical bells and are the 

 largest of all coelenterates. One species, the lion's-mane jellyfish, Cyanea, reaches 

 a diameter of 8 feet or more with tentacles 200 feet long. Huge shoals of this 

 animal are common in arctic or boreal seas, but, luckily, large ones do not range 

 far south. They possess a dangerous sting because of their large size. The blue 

 jellyfish, Aiirelia, is the most common jellyfish of the Atlantic and Pacific. This 

 genus reaches a foot across the bell and can produce an irritating sting. Pelagia 

 and Dactylometra, the speckled jellyfish, are two very beautiful and delicate 

 discomedusans of temperate to tropical waters. Both can produce painful stings. 

 The former is only a couple of inches across, but the latter reaches up to a foot 

 in width. 



The rhizostomes are jellyfishes without tentacles and are common in shallow 



