544 



THE BIOLOGY OF MARINE ANIMALS 



back and tail, and occasionally the legs. Extracellular luminescence is also 

 encountered in the mysid Gnathophausia. This animal discharges a lumi- 

 nous secretion from glands lying at the base of the mouth parts. The glands 

 consist of a reservoir, into which the cells discharge their contents, and a 

 duct opening to the exterior through a papilla (52). Among decapods some 



Photogen 

 band 



Foot 



Triangula, 

 photoge 

 organ 



Photogen 



cords in 



siphon 



Fig. 13.5. The Piddock Pholas dactylus, a Luminescent 

 Lamellibranch that Bores in Stone 



(Left) Ventral view of an animal; (right) appearance of a luminous animal in the dark. 

 (After Panceri.) 



of the deep-sea shrimps such as Plesiopenaeus, Systellaspis and Hetero- 

 carpus discharge a luminous secretion from glands about the mouth and at 

 the bases of the limbs in the anterior thoracic region (Fig. 13.4). These 

 glands are small and numerous, and each consists of a group of eosino- 

 philic cells discharging into a small central fundus, from which a fine duct 

 leads to the exterior. The secreted material is forcibly expelled away from 

 the animal, and gives rise to a luminous cloud (1). 



