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Journal of Experimental Biology 163,333-344 (1992)
Published by Company of Biologists 1992

PENETRATION OF WATER INTO BLIND-ENDED CAPILLARY TUBES AND ITS BEARING ON THE FUNCTIONAL DESIGN OF THE LUNGS OF SOLDIER CRABS MICTYRIS LONGICARPUS

DAVID P. MAITLAND ¹ and ARTHUR MAITLAND ²

¹ School of Biological Science, University of New South Wales, PO Box 1, Kensington, New South Wales 2033, Australia; Present address: Department of Physiology, Medical School, University of Witwatersrand, Parktown, Johannesburg, South Africa 2193
² Department of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, Scotland

Soldier crabs, Mictyris longicarpus Latreille, inhabit intertidal sand-flats of Eastern Australia. Their gill chambers are modified for both water circulation and air-breathing. Water circulates through the lower gill compartments. The upper regions of the gill chambers are air-filled and function as lungs. The deep vascular parenchyma lining the upper gill chambers, or lungs, is penetrated by a regular series of fine branching airways. Scanning electron micrographs of lung architecture are shown. Measurements relating to lung structure were made on plastic casts.

Because of the lung's design, water circulating through the lower gill compartments does not interfere with lung function. The airways are blind-ended and nonanastomosing, acting in effect as air-filled capillary tubes sealed at one end. A mathematical model and explanation show how the air trapped within this lung structure substantially reduces water penetration, despite surface tension (capillary) processes. This same lung design also facilitates the shedding of the lung cuticle at each moult.

Note:
Present address: Department of Physiology, Medical School, University of Witwatersrand, Parktown, Johannesburg, South Africa 2193.

Key words: capillary action, surface tension, lung, crab, moulting, Mictyris longicarpus, biomechanics

Accepted on September 19, 1991