66 MARINE ANIMALS OF MASSACHUSETTS BAF. 



Such is the Laomedea amphora, quite common on all the bridges 

 connecting Boston with the country, where, on account of the 

 large amount of food brought down from the sewers by the river, 

 they thrive wonderfully, growing to a great size, sometimes meas- 

 uring from a foot to eighteen inches in height. 



Sertularians. 



The Sertularians form another group of Hydroids closely 

 allied to the Campanularians, though differing from them in the 

 arrangement of the sterile Hydrae upon the stem. Among these 

 one of the most numerous is the Dynamena {Dynamena pumila 

 Lamx., Fig. 84), which hangs its yellowish fringes from almost 

 every sea-weed above low-water-mark. It is especially thick and 

 luxuriant on the fronds of our common Fucus vesiculosus. The 

 color is usually of a pale yellow, though sometimes it is nearly 

 white, and when first taken from the water it has a glittering 

 look, such as a white frost leaves on a spray of grass. Fig. 84 



Fig-84. Fig. 85. 



represents such a cluster in natural size, while Fig. 85 shows a 

 piece of the stem highly magnified, with a reproductive calycle 

 attached to the side of a sterile Hydra stem* Many of these 

 Sertularian Hydroids assume the most graceful forms, hanging 

 like long pendent streamers from the Laminaria, or in other 

 instances resembling miniature trees. One of these tree-like 



Fig. 84. Colony of Dynamena pumila ; natural size. 

 Fig. 85. Magnified portion of Fig. 84. 



