264 ANIMALS OF THE SEA FLOOR 



be regarded as protective or warning colouring, which 

 would be no advantage to an animal living in utter 

 darkness. Many of the animals themselves are blind, 

 and probably burrow in the soft ooze, or live a sedentary 

 life, clinging to hydroids, false corals, or sponges. 

 Others have large eyes especially adapted — at least, 

 in some cases — for the perception of faint gleams of 

 light. These are probably more active and predatory 

 types, guided to their prey by its own luminosity, or 

 sometimes having themselves luminous organs, which 

 serve as veritable searchlights. 



While the deep-sea fauna, as a whole, is by no 

 means of a primitive type, there are a few cases where 

 it does seem that animals of an antique type have 

 found in the deep sea a refuge from the more strenuous 

 competition of the thickly inhabited shallow waters. 

 This is notably the case with some Crustacea. The 

 Eryonidae (Fig. 183), a family of flattened lobster-like 

 animals, are the living representatives of a group of 

 which the remains are abundant in the rocks of the 

 Triassic and Jurassic Epochs ; the Homolodromiidae of 

 the deep sea appear to be the most primitive of the 

 existing crabs, and resemble some found fossil in 

 Secondary Rocks ; and certain deep-sea prawns (be- 

 longing to the families Penaeidse and Acanthephyridae) 

 are probably of more ancient types than their relatives 

 in shallow water. 



Finally, the extreme imperfection of our knowledge 

 of the fauna of the sea bottom in nearly all regions of 

 the world cannot be too strongly emphasized. Even 

 in shallow waters the smaller animals are almost 

 unknown, except in parts of the North Atlantic and 

 Mediterranean ; and those who have the opportunity 

 of dredging in depths exceeding 100 fathoms in any 

 part of the world may be assured that any animals 



