654 



THE BIOLOGY OF MARINE ANIMALS 



mucoid material in which calcium carbonate is deposited (Fig. 15.9). This 

 is largely in the form of aragonite (Pomatoceros). There is no organic 

 union between the tube and the animal. The tubes of serpulids have charac- 

 teristic shapes and arrangements, varying from species to species. They are 

 solitary (Spirorbis), aggregated (Serpula), semicolonial (Fibgrana) or 

 cemented together to form crusts or masses (Pomatoleios). The anterior 



Fig. 15.9. Polychaete Tubes 

 (Left) Calcareous tube of a serpulid Pomatoceros triqueter. Branchial crown, operculum 

 and anterior region of animal are shown protruding from the tube; (right) sand- and 

 gravel-encrusted tube of Lanice conchilega (Terebellidae). (After Mcintosh, 1922-23.) 



opening of the tube can be closed by a specially developed operculum 

 formed by modified gill filaments. 



CaC0 3 predominates in serpulid tubes, forming 90-99 % mineral matter; 

 organic matter is small, 3-6% dry weight. M2CO3 is sometimes present 

 {Serpula) (Table 15.1) (21, 23). 



The tube is secreted by tubiparous (major subcollar glands) lying in the 

 first setigerous segment. Alkaline phosphatase occurs in this region and is 

 possibly concerned with liberation of phosphate radicles as part of the 

 process of calcium secretion. The calcareous material secreted by these 

 glands is moulded by the collar at the anterior end of the worm. Normally 

 the tube is added to at the anterior end as the animal arows. In Pomato- 



