NATURE ADRIFT 



and one, Tlictys, about 6 inches long was caught in a herring net in the 

 northern North Sea near Wick in 1929. 



The second family is the Doliolidae. Doliolids are usually smaller, and 

 more delicate than salps and rarely reach an inch in length. They are barrel- 

 shaped and their eight or nine muscle bands encircle the body like the hoops 

 of the barrel. These also feed only on phytoplankton. Their life history is 

 more complicated than in the salps (Fig. 23; 7-1 1). Starting with what 

 corresponds to the aggregate individual in the salps is the sexual doliolid 

 called a gonozoid which has eight muscle bands. The fertilized eggs do not 

 grow in the body of the mother as do the salps but are shed into the water 

 to grow into small 'tadpoles' (p. 91), which become oozoids with 

 nine muscle bands. These reproduce asexually by the development of buds 

 which then migrate along the body of the oozoid to congregate on a speci- 

 ally grown dorsal 'tail'. These buds are of three kinds, the trophozoids 

 which are specialized only to catch food and remain attached to the oozoid; 

 phorozoids which are free swimming but sexless, and the gonozoids which 

 in their earliest stages are carried about attached to the phorozoids. The dis- 

 integrating remains of the oozoid often persists as an 'old nurse' with nothing 

 left but its muscular structure and so it is unable to feed. Only one species 

 is found in the northern part of the north-east Atlantic, Dolioletta gegenhaiiri 

 (= D. tritoiiis) (Plate XXXIX) but there are several in or near the Mediter- 

 ranean which can be drifted towards the area south-west of Ireland and 

 into the English Channel, one is Doliolimi uatioualis (Plate XX). 



The third family of the Thalicaea is the Pyrosomidae. Pyrosomes are 

 colonial forms in which many hundreds of very small individuals remain 

 attached together to form thimble-shaped colonies, the ones mostly found 

 are 3 or 4 inches in length but really big ones can reach 2 feet. They are only 

 found in warm water and very rarely reach the British Isles. As their name 

 implies pyrosomes (fire bodies) are brilliantly phosphorescent, looking like 

 an old-fashioned long incandescent gas mantle. 



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