EARLY POST-METAMORPHIC GROWTH, BUDDING AND SPICULE FORMATION IN THE COMPOUND ASCIDIAN CYSTODYTES LOBATUS

1. The colonial ascidian Cystodytes lobatus has a long breeding season (at least 6 months) and releases tadpoles sporadically throughout the day, indicating a long period of recruitment. 2. Tadpoles of C. lobatus were settled and reared in the laboratory in order to observe early growth, budding and spicule formation. 3. Budding is preceded by the formation of a new stomach at the posterior end of the esophagus and fits Nakauchi's Type I budding pattern. 4. Spicule formation begins within 5 days after settlement. The spicules appear to form in a particular region at the anterior end of the abdomen and migrate over the abdomen to form a single or slightly overlapping layer embedded in a "tunic spicular lamina." This lamina lies between the common tunic and the zooid cavity and forms a spicular sac in the tunic surrounding but separated from the abdomen of each zooid. It stains especially heavily for sulfated acid mucopolysaccharide; the spicules are concluded to form by cellular action in this organic matrix. 5. There is great variation among zooids in the quantity of spicules formed. These differences are maintained in the buds, resulting in colonies in which all zooids either have few or many spicules, and are therefore probably genetic in origin. 6. During budding the spicular sac becomes disrupted and appears to bud, resulting in a reallocation of the spicules to the buds and formation of separate spicular sacs around the abdomen of each bud. At budding there is apparently no disruption of bladder cell membranes in the tunic and no dissolution of spicules by the acids contained in the bladder cells.