Observations on the temperature and salinity relations of Lasaea rubra

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Abstract
In direct-transfer temperature tolerance experiments, Lasaea rubra was found to have a median lethal low temperature of – 3.5°C and a median lethal high temperature of + 39°C. If introduced to temperatures slowly, survival at extreme temperatures was improved, particularly at freezing temperatures; > 92°0 of animals survived at – 10 °C and + 40 °C if introduction from a holding temperature of + 18 °C took place over at least 1 h.Lasaea rubra are active at salinities between 15 and 60‰, indicating considerable tolerance of changes in body fluid osmolarity. In week-long exposure experiments more than 50 % of animals survived all salinities from 0 to 150‰; tight shell valve closure was maintained at extreme salinities.When exposed to declining salinity, Lasaea rubra progressively isolates its tissues from the environment as salinities fall below 18–20‰, and maintains shell valve closure below 8‰. These responses are symmetrically reversed in response to rising salinity.Salinity discrimination in Lasaea rubra is based upon sensing of external osmolarity, not external ionic concentrations.