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 Civerticula 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. 
