542 



THE BIOLOGY OF MARINE ANIMALS 



situated on five protuberances. There is a valvular structure at the dis- 

 charge pore of each of the secretory cells, and muscle fibres, which extend 

 between the gland cells from the dorsal body wall to the oesophagus, can 

 compress the gland and discharge its contents. Two kinds of inclusions in 



Aliform 

 notopodium 



Dorsal 

 tubercle 



Fig. 13.2. Chaetopterus variopedatus, a Polychaete 



that Discharges a Luminous Secretion 



{Left) dorsal view of the animal; (right) animal luminescing. 



these cells are yellow granules of luciferin and small colourless granules of 

 luciferase, both of which dissolve when extruded into sea water. In addi- 

 tion, mucus cells are present, which may discharge a mucous carrier for 

 the luminescent secretion (50). 



Luminescent copepods such as Metridia, Oncaea and Corycaeus pour 

 forth a luminescent secretion from photogenic cells grouped on the head, 



