LENGTH AND SPACING OF THE TUBE FEET IN CRINOIDS (ECHINODERMATA) AND THEIR ROLE IN SUSPENSION-FEEDING

The morphology of the primary tube feet in 15 species of comatulid (unstalked) crinoids from coral reefs in the Palau Islands and Lizard Island, Great Barrier Reef, was investigated using close-up underwater photographs of the tube feet taken in the natural habitat. Measurements of length of the tube feet and their spacing along the pinnule were taken from these photographs. Tube feet of species of the family Comasteridae have a mean length of 0.75 mm and a mean spacing of 6 tube feet mm-1. Tube feet of non-comasterid species occurring in the same environments have a mean length of 0.55 mm and a mean spacing of about 8 tube feet mm-1. The relationship between spacing and length of the tube feet is highty significant for both the Palau and Lizard Island samples (P<0.01). Species having longer and more widely spaced tube feet live partly concealed within the infrastructure of the reef and hold the arms and pinnules in a multidirectional posture. Species having shorter and more closely spaced tube feet perch on top of reef pinnacles or alcyonarians and form planar filtration fans normal to unidirectional currents or wave oscillations. Longer and more widely spaced tube feet in species dwelling within the reef infrastructure provide more efficient filtration in the slow, meandering flow prevailing there. Closer spacing of the tube feet in species exposed to near-mainstream flow provides a more efficient filtration mechanism at higher flow velocities. Reduced length of the tube feet in these species may be a consequence of closer spacing of the pinnules. Differentiation of these co-occurring species in spacing and length of the tube feet implies differentiation in food particles captured. This may in some cases constitute resource partitioning. Most species which overlap in living habits are significantly different in spacing and length of the tube feet. © 1979 Springer-Verlag.