The relationship between fine rings in the statolith and growth of the cubomedusa Chiropsalmus quadrigatus (Cnidaria: Cubozoa) from Okinawa Island, Japan

Abstract

Sixty-nine Chiropsalmus quadrigatus medusae were collected from Okinawa Island, Japan, in June-August 2000. The bell height ranged from 2.5 to 97.6 mm. The numbers of fine rings on polished statoliths were counted, and the coefficient of variation for the within-individual counts for the four statoliths was 3.3± 1.9% (mean::tSD, n=17). The slope of the linear regression of the number of rings against collecting date in 61 medusae was near 1.0, suggesting that the statolith rings are daily increments. The relationship between bell height and number of rings fitted a logistic growth curve. And, the relationship between statolith length and number of rings fitted the Gompertz growth curve. A check ring was present at a position of 5-10 rings from the center of each statolith. The backcalculated dates of check ring formation dated mainly from early to mid June, suggesting that the polyp of C. quadrigatus finished the metamorphosis to medusa and the medusa was liberated from a substratum during this period.