MODIFICATIONS TO AN OPTOCARDIOGRAPHIC METHOD FOR MEASUREMENT OF HEART-RATE IN A RANGE OF INVERTEBRATE SPECIES

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