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growth (Yokoyama, 1990) suggesting that the variability may have been partly caused
by individuals undergoing sexual reproduction.
Total setiger number, suggested by Anger et al. (1986) to be a better guide to body
size for spionids, can be estimated using the equation given by Morgan (1997);
I •
1
•
E
0.80 •
•S
toc
0 0.60
o
ba
o
— 0.40
1.40 y= 1.69x+ 1.56
1.20 r: O.854 0.854
1.00—*
0.20
0.00
Total setiger number = 9.85 + (93.6 x 5th setiger width (mm)) (Equation 2)
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• • * •
• • •
-0.90 -0.80 -0.70 -0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00
logm width (mm)
Figure 3.1 : Regression line of 5th setiger width against length for P. elegans, n=1398.
The smallest post-planktonic individuals found had 5th setiger widths of 0.13mm (or
22 setigers according to Equation 2 and 18-22 setigers by direct counting of a sample
of these individuals, n=25). This agrees with the findings of Hempel (1957) and
Rasmussen (1973) who suggested that P. elegans may settle from the plankton
anywhere between 11-20 setigers.
This study suggested that adult P. elegans sexually mature when they reach a 5th
setiger width of approximately 0.37mm. This corresponded to the smallest size that
branchiae were found on the 2nd setiger of P. elegans throughout the sampling period.
Since this method only determined the size at which males mature, the assumption
made here is that both males and females mature at the same size. This size
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