THE INVERTEBRATE LEGIONS 



95 



budd 



barbed, poisonous +Kr£Q.d 



eicloderm 



POLYP 

 (asexual) 



MEDUSA 

 (sexual) 



AFTER 

 DISCHARGE 



Fig. 26. The alternation of generations of a typical hydrozoayi coelenterate is shown 

 on the left. The asextial polyp and sexual medusa exhibit the same general hody plan 

 except that the medusa is greatly shortened, inverted, and has much more jelly than 

 the polyp. Coelenterate nematocysts, on the right, fire a poisonoiis thread into prey or 

 enemies on contact. 



skeleton). These are among the most common of seashore animals, but they 

 usually go unnoticed because of their small size. Among the many genera of 

 small hydroids is Ohelia, which shows, among its branches, two kinds of polyp 

 animals, a feeding one with tentacles and a reproductive one which produces 

 the sexual medusas by budding. At some times of year these little hydroid 

 medusas are very plentiful. 



There are many species of small hydroids like Ohelia. One of these is 

 Hydractinia, which is commonly found on the shells of hermit crabs (fig. 38^, 

 a case of mutualism in which the crab receives protection from enemies because 

 of the presence of the stinging hydroid tentacles and Hydractinia gets free 

 transportation. Most hydroids are too small to sting man, but a few have very 

 large nematocysts which are painful to touch. Phillips and Brady (1953) 

 list Lytocarpus of the eastern coast of Florida and southward as one of these. 

 This is a small colonial species like Ohelia and grows on rocks and pilings 

 among seaweeds. Treatment for the sting consists of thorough washing with 

 soap, followed by application of ammonia or calamine lotion to soothe the burn. 



Tuhularia, of temperate waters, is a beautiful reddish-pink hydroid that grows 

 unbranched out of a mat and reaches a height of almost 6 inches. The most 

 common small hydroid of the West Indies is Pennaria Cfig. 29), which looks 

 like a small Christmas tree. Not all hydroids are small, however. One gigantic, 

 noncolonial polyp, Branchiocerianthiis, reaches 6 feet in length and lives in the 

 ocean depths. 



The stinging coral, or fire coral, Millepora Qfig. 28 and fig. 144^, is not a true 

 coral, but is a hydrozoan related to hydroids. It grows in a great variety of 

 forms— branching, erect and bladelike, massive, or encrusting (often on sea fans). 

 They have dense, limy skeletons with very small pores through which the polyps 

 project. Stinging corals are major contributors to the formation of reefs in all 

 tropical seas. The sting of the West Indian species is only moderately painful 

 and the effects usually wear off in a few hours. Indo-Pacific fire coral can 

 produce more painful stings. 



