Studies on Ostracoda From New Zealand : Progressive Calcification and Ultrastructure of the Carapace of Some Adult Cytherocopina : (Crustacea:Ostracoda)

Abstract

Calcification of the ostracode carapace of form the calcareous foliated layer is progressive. The process begins with the outermost mineralised lamina of the cuticle―the protoostracum, and ends with the innermost mineralised lamina of the cuticle―the teloostracum. In trachyleberidacean cytherocopines the protoostracum selvage is the first inner margin (taction margin) of the shell, in contact with the vestment along the free-margin infold and with the ligament along the attached margin. The free-margin infold develops progressively during shell calcification and its inner margin moves from the protoostracum selvage to successive inward sites occupied by vestment as each new shell layer is formed. The hinge is part of the outer lamella of the shell and develops progressively following the formation of the protoostracum. In trachyleberidaceans with amphidont hingement in the adult stage, the tripartite merodont hinge of juvenile stages is the first stage in the progressive development of the amphidont hinge. In captive hemicytherids the calcification process began shortly after the maturation moult and was completed within about four days. All ornamentation is present on the epicuticle layer of the cuticle before any calcification takes place and is replicated by the protoostracum. Celation is a very limited process restricted to areas around setal pores and no other calcareous deposit is formed on the outside of the protoostracum. Moult retention, known to occur in palaeocopid ostracodes, but rare in other ostracodes, was observed in captive specimens of a species of ‘Ambostracon’ and probably has occurred in the Maastrichtian platycopid genus Ankumia. Noding occurred in one captive specimen of Hemicythere? brunnea (Brady) and in another of a new species of Quadracythere. A new model for the calcification which occurs in the organic matrices of the exocuticle and endocuticle layers of the cuticle is suggested. It involves the migration of ions from the hypodermis through a fluid medium separating the hypodermis from the epicuticle. Three new species of Bradleya and one of Quadracythere are described.