Observations on burrowing behavior in Limulus polyphemus (Chelicerata, Merostomata), with implications on the functional anatomy of trilobites. American Museum novitates ; no. 2436

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New York, N.Y. : American Museum of Natural History
"The functional morphology of burrowing was investigated in Limulus polyphemus with particular attention paid to the role played by the dorsal setae and prosomal shape. The burial process can be broken down into four discrete stages. Stage 1 involves active burial by downward flexion of the prosoma and a promotor-remotor swing (normal walking) by the prosomal legs. Sand is forced over the prosoma and anterior one-third of the opisthosoma, and a channel between these two structures is kept clear. Stage 2 involves no further burial, but rather active intake of water through one or both channels, deflection of the current back toward the gills underneath the opisthosoma, and expulsion of the current under one or both posterior opisthosomal projections. Stage 3 is the final burial phase and is effected both by forward walking and forceful flapping of the opisthosoma into the substratum; burial ceases when the last posterior opisthosomal projection is finally buried. The telson is covered throughout this process. Stage 4 is a long period of dormancy. The dorsal setae, distributed on the margins of the carapace, are mechanoreceptors that aid in keeping the organism buried. Their action is integrated with all other anatomical and behavioral aspects of burrowing, so that burrowing cannot be entirely disrupted by suppression of the tactile setae. Prosomal shape is at least partially explicable in terms of burrowing efficiency. The frontal arch is a necessary concomitant to a mode of burrowing that utilizes only normal promotor-remotor (walking) activity of the appendages; the arch effectively presents a horizontal edge to the substratum upon flexure of the prosoma of approximately 15 degrees. The high angle of slope of the margin of the carapace creates a thick wall of sediment that covers the rest of the body and allows burial within a minimum amount of space. The coaxial exite of the sixth prosomal appendage is a curved structure that probably deflects the current of water entering at the channel back toward the opisthosomal gill appendages, although they do not carry out this function alone. It may or may not be used to clean the gills, which is the function usually attributed to it. Limulus polyphemus possesses many anatomical similarities with trilobites. Detailed knowledge of the functional morphology of L. polyphemus may, if carefully applied, serve as a model for interpretation of trilobite morphology hitherto incompletely understood. In particular, the nature and role of the sensory dorsal setae and the functional aspects of the anterior arch in L. polyphemus appear to have a direct bearing on the interpretation of closely comparable structures in certain trilobites"--P. 16-17.
17 p. : ill. ; 24 cm.
Includes bibliographical references (p. 17).