452 



THE BIOLOGY OF MARINE ANIMALS 



pathy with diurnal and tidal changes ; such respiratory cycles are probably 

 due to cyclic variations in levels of muscular activity (p. 153). Diurnal 

 phasing of locomotory activity has now been recorded for many marine 

 animals, e.g. turbellarians, gastropods and starfishes. 



Light 

 Dark I Continuous darkness 



V ■ f 



24 hours 



i i r 



WM^JWV 



ght 



1 Dark 

 Night Day 



Fig. 10.21. Activity of Metridium senile over a Period of 

 48 Days (Kymograph Records) 



Alternating 12-hour periods of dark and light correspond to night and day at the 

 beginning of the record; at the end they are reversed. During these periods a light- 

 controlled rhythm is apparent. In the intermediate period of prolonged darkness a 

 phasic rhythm develops which is unrelated to external diurnal or tidal rhythm. (From 

 Batham and Pantin (9).) 



Defaec. 



Dark L i$ht 12 hours Shr ivelled 



D§ Qo^O 



Fig. 10.22. Kymograph Record of Activity in the Sea Anemone 



Metridium senile 



A pronounced light-controlled rhythm in the first half of the record is abolished by 

 feeding. The sketches below show the appearance of the anemone at successive periods. 

 (From Batham and Pantin (9).) 



Convoluta roscoffensis is a littoral species of flatworm that executes 

 rhythmical tidal migrations. These movements bring it to the surface of 

 the sand during tidal ebb, thereby exposing its algal symbionts to light 

 (p. 617). Rhythmic activity with tidal phasing continues in this animal in 

 the laboratory, in absence of tidal influences. Starfish (Astropecteri) 



