PELAGIC ANIMAL LIFE 



575 



Together with these forms we often find Cestus veneris, one of the Ctenophc 

 Ctenophores, a class including many pelagic forms, both surface and deep 

 sea. Four species of Ctenophores have been observed in the arctic 

 region : Mertensia ovum, Pleurobrachia pileiis, Bolina mfundibulmn, and 

 Beroe cuaimis. After studying the collections of the "Belgica" and 

 the "Michael Sars," Damas and Koefoed state that Pleurobrachia pileus 



..M^'-pff^ 



Fig. 409. 

 Physalia. (I-'roni Steuer. ) 



is a coast form occurring from the channel 

 infundibuluin and Beroe cucumis have a 

 occur in deeper water, for instance, in the 

 fjords ; Mertensia ovum is an arctic form, 

 wegian fjords. - 



to Spitsbergen ; Bolina 

 far wider distribution, and 

 deep waters of Norwegian 

 also found in deep Nor- 



all the higher groups of Pelagic larv«. 



• pelagic, from the medusae to 



forms of the latter the general 



lead a bottom life while the 



among the medusae the mature 



swimming or floating, young 



Pelagic larvae are encountered among j 

 animals either holopelagic or mero- 

 the fishes. Among the higher organised ■>' 

 rule seems to be that the mature stages j;' 

 eggs and larvae are pelagic, whereas 

 stages are generally pelagic. Pelagic, 



stages are found in the echinoderms '"'^ (starfishes, holothurians, 

 etc.), annelida, bryozoa, and in various '"' crustaceans from the sessile 

 cirripeds to the lobsters and crabs ; snails and mussels also have pelagic 

 young. 



In spring especially the coast-waters teem with the larvae of all 

 these animals, the larval forms very often differ from the adult, and an 

 enormous amount of work has been devoted by zoologists to the 

 description of all these forms. Some of these larvae seek the bottom 

 after a lapse of only a few days, but many species lead a long pelagic 

 life and during this period go through metamorphoses, among the most 



