BURROW VENTILATION IN THE TUBE-DWELLING SHRIMP CALLIANASSA-SUBTERRANEA (DECAPODA, THALASSINIDEA) - I - MORPHOLOGY AND MOTION OF THE PLEOPODS, UROPODS AND TELSON

The morphology of the pleopods, uropods and telson of the tube-dwellin g shrimp Callianassa subterranea have been studied using dissection mi croscopy and scanning electron microscopy. The kinematics of these app endages were examined by motion analysis of macro-video recordings of ventilating shrimps in transparent artificial burrows. The pleopods sh ow the usual crustacean biramous anatomy, but all segments are rostro- caudally flattened. The protopodite bears a triangular medially orient ed endopodite and a scoop-shaped exopodite, The contralateral endopodi tes are linked by the appendix interna, ensuring a perfect phase relat ionship between contralateral pleopods, The outer rims of the exopodit es are fringed with long fern-leaf-like plumose setae bearing flattene d setules, These setae have very mobile joints and can be turned cauda lly, The slits between contralateral endopodites have rims of leaf-lik e setae as well. Setae of the same leaf-like type fringe the uropods, but these are nonmotile. The telson has a narrow fringe of leaf-like s etae, locally interrupted by long mechanoreceptory setae. A shrimp, wa ndering through the burrow or resting, holds its pleopods against the abdomen with the exopodites and their setal fringes retracted medially . The uropods are folded medially as well, probably to reduce the shri mp's drag. During ventilation, the uropods are extended against the tu be wall, leaving only a small opening for flow ventral from the telson , and the pleopods beat at a frequency of approximately 1 Hz (0.9+/-0. 2 Hz). Fourier analysis of pleopod kinematics showed that the motion p attern of the first flow-generating pleopod pair (PP1) consisted mainl y of the first harmonic (75%) and to a lesser extent of the third harm onic (20%), resulting in almost perfect sinusoidal motion. The motion patterns of PP2 and PP3 could be modelled by assigning pure sinusoids with a 120 degrees phase shift and a rostro-caudal ranking to the thre e pairs of pleopods.