Scaling patterns in the Antarctic brachiopod Liothyrella uva (Broderip, 1833)

Scaling patterns of shell thickness, shell volume, total animal volume, internal tissue volume and mantle cavity volume in the brachiopod Liothyrella uva (Broderip, 1833) were investigated in relation to shell length. Exponents from double logarithmic regressions were 0.66, 2.77, 3.12, 3.06 and 3.34, respectively. The coefficients 3.12 and 3.06 were not significantly different from a cubic relationship, but the exponents 2.77 (shell volume) and 3.34 (mantle cavity volume) were different from 3.00. The amount of shell material, therefore decreases in relation to other brachiopod tissues as animals grow, while the mantle cavity gets relatively larger. These results suggest that large brachiopods may suffer space constraints because of the volume needed to house the lophophore and this has implications for all aspects of the brachiopods life style. Data on ash-free dry weight (AFDW) assessments of shells from an early winter sample showed a slope of 2.78, which is consistent with the shell volume relationship. A sample from mid summer, however, produced a relationship which was different in large and small animals. In individuals < 31.3 mm in length the exponent was 2.73 (which was indistinguishable from the 2.78 for the winter sample); however, the exponent was 3.73 for animals greater than this. 31.3 mm was also the minimum length of brooding females in this study. These data indicate that the function of caeca changes when brachiopods become reproductive.

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