shape of foot associated with anchorage are brought about by action of 

 intrinsic musculature of foot and visceral mass against a hydroskeleton 

 provided by blood filling the large sinuses. Downward movement is 

 associated with forward movement, so that the animal moves obliquely 

 downward. Forward movement is caused by asymmetry of foot as it protrudes, 

 the posterior end being anchored more or less immediately below posterior 

 margin of shell by the heel, while anterior end of foot is thrust forward 

 some distance. If downward component of movement is prevented, as on a 

 hard substrate, the clam moves horizontally. In both cases the shell 

 makes a rocking movement. Essentially the same actions are responsible 

 for horizontal movements of postlarval clams on hard substrates. 

 Variations in time sequence of digging activities come largely from 

 variation in time required for foot to obtain anchorage in the early 

 stages. Thus, early sequences take longer than later ones. This period 

 ends when hinge margin is level with surface of substrate. Then time 

 intervals between movements drop substantially, then slowly and gradually 

 increase until the sequence is complete. Total depths (to uppermost surface 

 of shell) reached by hard clams at completion of burrowing ranged from 1.4 

 to 9.2 cm for 84 separate trials. Gradual increase in time sequence, after 

 movements related to initial anchorage, may arise from a gradual increase in 

 resistance as the clam moves deeper. On the other hand, increasing time 

 interval could be an expression of tiring. It has been suggested that 

 cessation of burrowing is caused by fatigue, but this is not likely, because 

 clams will burrow repeatedly if removed from the substratum immediately on 

 completion of a sequence. Because tips of siphons maintain contact with 

 surface of substrate and extension of siphons follows each downward movement, 

 cessation of burrowing may be a response to stimuli originating from siphons. 

 Stretch receptors and other proprioceptors may be acting. - J.L.M. 



86 



J7 



Ansell, Alan D. 1962. 



The functional morphology of the larva, and the post-larval development of 

 Venus striatula (DaCosta) . J. Mar. Biol. Assn. U.K. 42(2): 419-443. 



Within the Veneracea the Family Veneridae forms a group of closely related 

 suspension-feeding bivalves, which have retained the ability to move hori- 

 zontally and vertically close to the surface in relatively soft substrata. 

 The Veneridae have evolved along unspecialized lines, and the slow rate of 

 metamorphosis to the adult form is associated with lack of special adapta- 

 tions. Venus (=Meraenaria ) mevcenavia is not mentioned. - J.L.M. and M.W.S. 



Ansell, Alan D. 1962. 



An approach to sea farming. New Scientist 14(288): 408-409. 



Rate of increase of phytoplankton is controlled mainly by light intensity 

 and ambient temp. Nutrient levels in the sea usually are low, and dense 

 phytoplankton populations occur only rarely. Concrete 1,000 liter (220 gal) 

 tanks were built on the grounds of a generating station at Poole, Dorset, 

 England. Scrubbed flue gas was added as necessary to renew CO2. N and P 

 fertilizers were added as sodium hydrogen phosphate and ammonium sulphate. 

 A "pure" plant crop was ensured by inoculation at time of fertilization with 

 sufficient algal cells to swamp competitors. The alga Phaeodactylum was 

 used because it tolerates extreme conditions and competes successfully with 

 all naturally occurring species that appeared in tanks. Artificial light 

 usually was not necessary because satisfactory growth was obtained almost 

 all year, except early in January. Even when water temp fell to 1°C growth 

 continued, although more slowly. The final crop at low temp may equal that 

 obtained in summer. Although this was batch culture, continued growth could 

 be obtained by harvesting frequently. Yields of up to 7 . 5 g dry organic 

 matter/tank/day in March and 16.5 g/tank/day in May- Aug were obtained. 

 Average composition of Phaeodactylum was 47% protein, 20% fat, and 6% carbo- 

 hydrate, with 27% ash. Calculated food value, about 4,000 calories/g, com- 

 pared favorably with many other plant crops and high proportion of protein 

 to dry weight was important. Under the most favorable conditions 80% of 

 the phosphate added may be returned, and a similar yield of nitrogen. 



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