149 



The large feathered bristles that decorate the 

 limbs or tail of many plankton Copepoda have no 

 doubt the same function in assisting flotation. In 

 the genus Calocalanus (Fig. 52), for example, the 

 tail setae are large and brilliantly coloured feathery 

 plumes, and in one species, C. phimulosus, one of 

 these setae is of relatively enormous size, five or six 

 times as long as the body of the animal itself. 



Among the most singular of plankton Crustacea 

 are the Phyllosoma larvae (see Fig. 28, p. 72) of the 

 Spiny Lobsters and their allies (Scyllaridea), which 

 have been already described. These larvae are 

 sometimes found far out at sea, and it seems likely 

 that their larval life is unusually prolonged, and that 

 they may be drifted to great distances by ocean 

 currents. At all events, they are well adapted for 

 pelagic life, since the broad flat body, hardly thicker 

 than a sheet of paper, can be sustained in the water 

 like a " hydroplane " by comparatively slight efforts 

 of the swimming legs. 



The watery character of the body, together with 

 the thinness of the exoskeleton, helps to explain the 

 glassy transparency which is a feature of most 

 plankton Crustacea. This transparency has been 

 regarded as a protective adaptation rendering the 

 animals inconspicuous in the water, and it has 

 indeed that effect to human eyes, but it is very 

 doubtful whether the animals derive much benefit 

 from this. Many of the animals such as Herring 



