Size, shape and the distribution of organic matter in the Recent Antarctic brachiopod Liothyrella uva

The living terebratulid articulate brachiopod Liothyrella uva (Jackson 1912) was sampled from a shallow water population at Signy Island, South Orkney Islands, Antarctica. Neither shell height nor shell breadth were directly proportional to length and as a result there was a change in shell shape with size (and hence age); this change was small but statistically significant. The proportion of the total organic matter found in the shell and internal (mantle) tissues also changed with size. In small (5–7 mm length) brachiopods 70–80% of the total organic matter was located within the shell; this fraction decreased with increasing size until above about 25 mm length the proportion of organic matter in the shell was constant at 30–45%. Variability in this measure was influenced by infection with endolithic red algae. Punctal density was independent of size with a mean value of 95.7 per mm2 [SE (standard error) ± 2.2], which was greater than in populations sampled from higher latitudes. With increasing shell length there was a slight increase in the size of puncta close to the shell edge. In all morphometric measures the range of variation observed was similar to that described from populations of Liothyrella from other areas of the Southern Ocean