Carbonic anhydrase (CA), the enzyme which catalyzes the reaction CO2+H2O⇌H2CO3, was found in both active and resting accessory boring organs (ABO) of Urosalpinx, using a modification of the Waldeyer and Häusler (1959) technique in which the tissue section is floated on the substrate solution. The intense reactivity of this gland exceeded the activity of other pedal tissues of this muricid gastropod. The ventral pedal gland of the female also exhibited strong activity, but theconcentration in this tissue was not as intense as that observed in the ABO.

No discernible differences between the microvilli of resting and boring ABOs were noted after fixation in acetone, formalin, or glutaraldehyde. However, notable nuances in reactivity of the pedal structures occurred when the comparative effect of fixatives was evaluated.

All variations of the immersion technique, as opposed to flotation procedures, exhibited a strong stain only in the microvilli of active ABOs, and little or no activity in resting ABOs. This difference between active and resting ABOs (immersion technique only) appears to be due to the binding (chelation) of calcium with subsequent replacement of cobalt (probably as a carbonate complex) in the substrate.

The markedly greater CA activity in the ABO, relative to other secretory tissues inthe snail, suggests a vital role for this enzyme in the process of penetrating shell. Thelow pH of the secretion from the active ABO during boring indicates that at least one phase of the boring process is a chemical reaction associated with production of acid.