470 



DEPTHS OF THE OCEAN 



generally find the most abundant animal life among the algse 

 in localities where wave-action is most effective. Most of the 

 non-attached forms are in no way directly dependent upon the 

 algae-vegetation. 



It will be evident that attachment to fucus and laminaria 

 is not biologically essential, if we bear in mind that the same 

 animal forms which attach themselves to these plants occur 

 also on rocks and stones. The vegetation merely increases 

 the area available for the attached forms. Nor is any particular 

 plant essential for any particular species of animal. No doubt 



on the Norwegian west coast 

 Laomedea flexuosa and Clava 

 sqiianiata nearly always attach 

 themselves to Ascophylhmi, while 

 Obelia o-eniculata and some others 

 prefer laminaria, but this is chiefly 

 owing to the tides. On the 

 Skagerrack coasts, where tides 

 are inconsiderable and irregular, 

 we find even in the fucus belt 

 forms like Coryne (see Fig. '^ZZ)> 

 Tubularia, and Obelia geniculata, 

 though on the west coast of Nor- 

 way they grow only among the 

 laminaria and at a lower depth. 

 These forms cannot stand exposure 

 for any length of time, and they are 

 therefore not to be found in places 

 where the ebb regularly goes back 

 a long way. The forms met with 

 in the tidal area cannot, however, be in any way dependent 

 upon the ebb-tide for their existence, seeing that they occur 

 numerously also on the coasts of the Skagerrack, where tides 

 are scarcely felt. Instances of this are furnished by Clava, 

 Campanularia Jlexuosa, and Dynamena pumila, but the fact that 

 these forms are able to withstand exposure for considerable 

 periods of time makes it possible for them to occupy a far 

 more extensive area than would otherwise be the case. 



So far as the structure of their organs is concerned, the 

 unattached forms in the algae-fauna are particularly well 

 equipped for gripping, climbing, or creeping about among the 

 hydroids and the red bushy alg^e that usually grow in quantities 

 upon the laminaria. The crustaceans (caprellids and amphipods) 



Fif5. 33. 



Coryiic pusilla, Gaertn. 



(After Hincks.) 



