ABYSSAL BENTHIC ORGANISMS 395 



only animals belonging to taxons higher than species may have 

 survived from preglacial periods. The family of actinians, the 

 Galatheanthemidae (Carlgren, 1956), which hitherto has been re- 

 corded only from trenches below some 6000 m, is an example of 

 such survivors. 



Influence on Sedimentation 



Many years ago Dai win (1881) established the fact that burrow- 

 ing land animals such as earthworms have an important effect in 

 mixing the uppermost layers of the soil. A similar effect may be 

 observed in any shallow water locality where Arenicola, for exam- 

 ple, is abundant. In contrast to this only rather recently has the 

 same phenomenon been taken into consideration in deep-sea sedi- 

 ments. Bramlctte and Bradley (1942, p. 22) may be the first to 

 note that " apparently mud-feeding animals have played a significant 

 part in reworking the sediment, even on the floor of the abyssal 

 parts of the ocean." In the last few years with the great improvement 

 in deep-sea coring and photography, much evidence has accumu- 

 lated for this sort of mixing. Among recent publications may be 

 mentioned papers by Bernard (1958) and Perez (1958) with observa- 

 tions and photos from the French Bathyscaphe. They show small 

 mounds up to 60 cm in height, together with holes and cavities of 

 many various sizes on the bottom. These must be due to the ac- 

 tivity of various larger bottom animals like crustaceans {Ethusa, 

 Galatheopsis) and other animals known from deep-sea trawlings. 

 From cores Picciotto and Arrhenius (unpublished) have found some 

 beautiful examples of mixing down to at least 40 cm below the 

 surface of the sediments. They suggest in one case that a worm 

 channel has penetrated down to 26 cm; this might be one of the 

 tubiculous polychaetes or one of the Pogonophora (cf. Arrhenius, 

 Fig. 7, p. 142). Another example shows an organism which has dug 

 a cavity into the bottom and this cavity has become filled with 

 modern, highly radioactive sediment. Such a cavity could have 

 been made by an irregular sea urchin like Echinosigra or some 

 similar genus. 



