MICROGROWTH BANDS IN CHITONS: EVIDENCE OF TIDAL PERIODICITY

Microgrowth bands of typical molluscan appearance were clearlyrevealed by the acetate film technique in the sutural laminaeof the large chitons, Amaurochiton glaucus, Sypharochiton pelliserpentis,Cryptoconchus porosus and Acanthopleura granulata. In all speciesthere was a cyclical pattern, averaging close to 28 bands percycle suggesting that one growth increment was laid down pertide. Band widths were unusually small compared with those ofbivalves or gastropods, probably because the shell is dividedinto eight growing plates. Overall rates of growth calculatedfrom band widths were 1–2 mm per month, comparable withfield estimates. (Received 13 February 1984;