Trilobite cuticle microstructure and composition

Abstract

Previous literature on the microstructure and composition of the trilobite cuticle is reviewed.The microstructure of the cuticle of Asaphus raniceps Dalman sensu Angelin ( 1854) is described in detail, and a table outlining the major features of the cuticles of fourteen other trilobite species is included.In Asaphus raniceps and some other species, two main regions of the cuticle are consistently present: an outer layer characterized by perpendicular prisms, representing about one-fifteenth of the total thickness of the cuticle and an inner area forming the bulk of the cuticle.In the inner area of many cuticles, characteristic primary microstructures are fine perpendicular canals, a variety of wider canals, and horizontal laminae.Three types of tubercle are distinguished from thin-sections.Inorganic analyses of Asaphus raniceps show that the cuticle consists largely of calcite.Decalcification of this cuticle with E.D.T.A. left organic residues.A LARGE number of incidental observations has been made on the trilobite cuticle, usually during the course of systematic descriptions.However, no author has studied the cuticle of a wide range of trilobite species in the thorough way that Lindstrom (1901) and latterly Clarkson (1967Clarkson ( , 1969) ) have examined visual organs.Attempts at comparing trilobite cuticles with arachnid or crustacean cuticles have therefore often been based on inadequate evidence, and in some cases recent work on extant arthropod cuticles has been totally disregarded.