Modifications to an optocardiographic method for measurement of heart rate in a range of invertebrate species

Abstract

A non-invasive technique developed by Depledge & Andersen (1990) on a crab and a lamellibranchiate was used in this study to measure heart rate activity in a millipede, centipede, spider, two scorpion species, two crab species, three insect species and the garden snail. A novel technique to confine smaller arthropods in an aluminium foil bag provided with a 7 mm by 7 mm opening allowed heart rate measurements to be done on spiders, insects, centipedes and scorpions without direct body contact of the probe. For the crab and the garden snail a plastic device to hold the reflective optocoupler (ROC) probe was glued externally over the heart region. The amplitude of the heart rate signals in 1 mm depth water as medium was about 8% less than those in 1 mm of air. Four millimetres of water as medium reduced the amplitude signal by 90% when compared to zero thickness. With 4 mm of air as medium the amplitude signal decreased by 80%. The erroneous electronic circuit diagram published by Depledge & Andersen (1990) is corrected and redrawn.