1433 



Pannella, Giorgio, and Copeland MacClintock. 1968. 



Biological and environmental rhythms reflected in molluscan shell growth. 

 In Paleobiological aspects of growth and development, A symposium. 

 Donald B. Macurda, Jr. (edj . Paleont. Soc. Mem. 2, J. Paleontology 42 

 (suppl. to no. 5), Pt. 2 of 2: 64-80. 



Living Mercenaria mercenaria were notched at growing edge of shell and 

 planted in the intertidal zone in Barnstable Har. , Mass. Shells from 2 lots, 

 killed 368 and 723 days after planting, had as many small growth increments 

 as the numbers of days from notching to killing. Superimposed on daily 

 growth records were thin daily increments of winter, and 14-day cycles of 

 thick and thin daily increments caused by tides. Comparison with tidal 

 records showed that, for each 14-day cycle, thin daily increments formed 

 during neap tides and thicker increments during spring tides. Such patterns 

 also are present in hard clams from the subtidal zone, but rarely as pro- 

 nounced. Spawning patterns differ from winter patterns. Spawning induces 

 an interruption of regular deposition followed by a series of thin daily 

 increments. Continuous sequences of bidaily patterns also are common in 

 M. mercenaria, one thick daily increment followed by a relatively thin one. 

 Clearest 14-day cycles were seen in shells of Tridacna squamosa. Temp, 

 tides, reproductive activity, substrate, depth of water, and age affect 

 molluscan growth. Preliminary data from Mercenaria and other fossil 

 bivalves suggest a decreasing trend in mean number of days per lunar month 

 from 30.07 in the Pennsylvanian, 29.96 in the Cretaceous, 29.82 in the 

 Eocene, 29.38 in the Miocene, to 29.13 Recent. - J.L.M. 



1434 



Pannella, Giorgio, Copeland MacClintock, and Maxwell N. Thompson. 1968. 



Paleontological evidence of variations in length of synodic month since late 

 Cambrian. Science 162: 792-796. 



Circadian rhythms regulate almost universally the world of living matter. 

 They often leave records in skeletons of continuously growing organisms. The 

 question arises: do daily bandings record solar or synodical time? Experiments 

 on bivalve mollusks have led to the conclusion that solar time is the basic 

 unit, and that synodical time is expressed in thickness of increment. Most of 

 the data reported were from bivalves. For control and comparison counts from 

 the recent bivalve Mercenaria mercenaria from New England were recorded. 

 Number of increments/month in 6 hard clams varied from 28.9 8 to 29.58 for an 

 average of 29.17. In general, growth patterns record fewer increments than 

 actual days, and this average value is 1% less than the actual value for the 

 synodic month. The change in length of synodic month for the Miocene, based 

 on a count from one specimen of Mercenaria campechiensis ochlockoneensis (18 

 million yrs BP) that showed the same shell structures and growth patterns as 

 recent M. mercenaria, was higher than the one predicted by astronomical 

 calculations. Values for Eocene and Upper Cretaceous also were higher than 

 predicted. Analysis of fossils dating back to Upper Cambrian (510 million yrs 

 BP) suggested that slowing of the earth's rotation has not been uniform. 

 These observations and speculations show that by using growth patterns of 

 organisms it will be possible to shed light on events that affected the 

 general distribution of oceans and continents in the past. Two breaks in 

 slope of the curve describing length of synodic month through 510 million 

 yrs of geologic time, in the Pennsylvanian and Cretaceous, may be related to 

 changes in distribution of continents, ocean, and adjacent shallow seas, and 

 their effects on rotation of the earth. - J.L.M. 



1435 



Parker, C. 1881. 



Poisonous qualities of the starfish. The Zoologist 5: 214. 



Postulates that a toxic secretion, liberated by the sea star and introduced 

 between the valves of a clam, is responsible for opening the valves. - from 

 Burnett, Ecology 41(3), 1960 - J.L.M. 



402 



