. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 68 DAVID R. FRANZ be present, and so on. The problem is to discriminate between a true annual growth interruption mark and a mark resulting from some other cause such as damaged outer lip. Consequently, the decision as to whether a mark is indeed a true annulus is highly subjective and in many cases impossible. Drills which were damaged or in which the cause of the interruption was in doubt were not included, so that data in Table I represent 168 out of an initial 224 snails. It is evident from the table that there is a clos
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 68 DAVID R. FRANZ be present, and so on. The problem is to discriminate between a true annual growth interruption mark and a mark resulting from some other cause such as damaged outer lip. Consequently, the decision as to whether a mark is indeed a true annulus is highly subjective and in many cases impossible. Drills which were damaged or in which the cause of the interruption was in doubt were not included, so that data in Table I represent 168 out of an initial 224 snails. It is evident from the table that there is a close correlation between the mean weight of snails in each of the first four growth mark categories and the mid- points of weight components believed to correspond to the 1966 through 1969 year classes (Fig. 3). The correlation between the range in weight of each of the in E o i_ C9 I 4- 3' 2 I -. 1 1 1 I I I I 10 15 20 30 40 Length (mm) FIGURE 4. Double logarithmic plot of shell length and shell weight, pooled October 1969 sample. Curve is fitted visually. growth mark categories and the range of their respective year class components is also close, with the exception of the group of snails with two growth marks. The excessive scatter in this group probably results from failure to discriminate between true and false annuli. This is particularly difficult in older drills because of erosion of the spire and partial masking by subsequent shell growth of a portion of the earlier annuli. Cumulative growth Figure 5 is a cumulative growth curve based on the analysis of both shell weight and length. When the cumulative shell length is plotted against age, the expected sigmoid growth curve is produced with a point of inflection near. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marine Biological Laboratory (Woods Hol
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
