Penetration of Water Into Blind-Ended Capillary Tubes and Its Bearing on the Functional Design of the Lungs of Soldier Crabs Mictyris Longicarpus

Abstract

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.