Discussion

Abstract

Professor T. B arnard said that some of the burrows and infillings of burrows shown by Dr Bromley appeared to be funnel-shaped or irregularly shaped, and to branch; these characters were unusual for burrowing Crustacea. Many burrowing arthropods tended to burrow backwards and the burrow then filled in after the animal had disappeared from sight. One of the figures shown by Dr Bromley in his lecture suggested that an arthropod with one large claw (like a fiddler crab) was moving forward in the burrow and digging in this manner; this would be unusual for any arthropod of this type. The speaker would therefore like to ask the author whether he knew of any Recent arthropod which made a funnel-shaped or ramified boring or burrow and which moved backwards and forwards within a burrow when made. He also wondered how the arthropod managed to stabilize the walls of the burrow in soft sediment, since arthropods did not secrete mucus. The numerous burrows, and bioturbated chalk occurrences spread over a large area, would suggest population explosions at many levels within the Chalk. It was perhaps difficult to imagine a large number of arthropods occurring without leaving some trace of their hard parts, for claws and appendages were extremely rare within the Chalk. He would therefore suggest that much of the bioturbation and burrowing was of annelid and not arthropod origin. The bathymetric ranges of modern arthropods was large, going down to depths of 2000m or more; however, many of these deep-water living forms