178 INVERTEBRATE ZOOLOGY 



ANTHOZOA 



A SEA ANEMONE (Metridium) 



This animal, which is the largest sea anemone along the North 

 Atlantic coast, is often plentiful on rocks, shells, and docks in 

 shallow water. Place an expanded individual in a deep dish of 

 water and observe its shape, color, and method of attachment. 

 The upper end of the columnar body is called the disc, and in its 

 center is the elongate, slit-like mouth, surrounded by the numer- 

 ous tentacles. The lower end of the animal is called the foot. It 

 is often expanded and is not permanently attached to the sub- 

 stratum ; the animal has some locomotory powers and can slowly 

 move from place to place. 



Study the form of the mouth. Note the thickened lips at 

 each angle of the mouth; these form a ciliated groove, called 

 the siphonoglyph, through which the genital products reach the 

 outside. In some individuals only one siphonoglyph is present. 



Study the surface of the disc and the tentacles. The former 

 is frequently expanded and thrown into folds and lobes. The 

 tentacles are elongated diverticula of the disc and are hollow. 

 They are charged with nettle cells and are the principal organs 

 of defense and offense. They are also useful in feeding ; after 

 the nettle cells have stung the small animals which constitute 

 the food of the sea anemone, the tentacles place them in its 

 mouth. The tentacles are not all the same size, those nearer 

 the mouth being the larger and the older. 



Note the character of the columnar body. It is pierced by 

 small pores through which long, white, glandular threads, armed 

 with nettle cells and called acontia, may be thrust when the 

 animal is irritated. 





