SPICULE FORMATION IN THE NEW-ZEALAND ASCIDIAN PYURA-PACHYDERMATINA (CHORDATA, ASCIDIACEA)

The New Zealand solitary ascidian Pyura pachydermatina (Phylum Chordat a, Suhphylum Urochordata) is a sessile filter feeder in rocky wave-swe pt coastal areas, The body is on a long stalk;both are covered by a to ugh fibrous tunic, Two types of spicules are formed in vascularized ar eas: ''antler-shaped'' branched spicules of amorphous calcium carbonat e in blood sinuses in the body tissues and ''dogbone-shaped'' knobbed calcitic spicules in the tunic blood vessels, Both types form extracel lularly, contain intraspicular organic components and are covered by a n organic matrix coat within an epithelium of sclerocytes. SEM and TEM analysis of the spicules and their formation is included, along with calcein incorporation data used to estimate rate of growth, A comparis on with spicules of other ascidians and in selected other organisms is included, with comments on the shared features of biomineralization t hat these disparate groups exhibit.