Discovery of a new type of shell structure within the organophosphatic brachiopods and the status of the family Curticiidae

Abstract

A new representative of the family Curticiidae, Curticia? pattersonensis (Class Lingulata, Brachiopoda), is described from the upper Middle Cambrian (Cedaria-Crepicephalus zone) of the Great Basin, USA. It displays a new type of shell structure which is characterized by a baculate secondary and a columnar tertiary layer, a combination previously unreported within the organophosphatic brachiopods. Examinations of the surface of the larval shell of Curticia? pattersonensis sp. nov. revealed in addition an previously unreported ornamentation typified by hemispherical pits of uniform size that exceed the larval shell by a certain distance. This is in strong contrast to the pits of Curticia minuta which are variable in size and restricted to the larval shell questioning the co-generic position of the new taxon. The formation of the pedicle opening by means of resorption of the shell from a juvenile foramen to a adult delthyrium known from Curticia minuta and supposed to be characteristic for the whole family could not be confirmed by observations on the ontogeny of Curticia? pattersonensis sp. nov. In fact a broad triangular delthyrium seems to be present in all growth stages of the new taxon. The observations on the shell structure and ontogeny of C.? pattersonensis sp. nov. indicate that the present systematic position of the Curticiidae within the superfamily Acrotretoidea and the current definition of the family need to be re-considered.