LARVAL SETTLING BEHAVIOR INCYANEA CAPILLATA(CNIDARIA: SCYPHOZOA)

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Abstract
The planula of C. capillata is studied in the laboratory to determine if it responds to environmental cues in a way which may account for the distribution of its sedentary scyphistoma stage in the field. The effect of gravity, dissolved gases, surface texture, and illumination on larval settlement is examined using 2 cm2 plastic coverslips as substrate supported above the bottom of glass containers so that larval activity could be observed and the position and orientation of attachment determined. Planulae are geopositive and slow-moving in well-aerated sea water, and become active and geonegative under conditions associated with local depletion of O2. This active period ends in attachment upside-down (P < 0.001) on a horizontal surface close to the bottom of their container. They attach with greatest frequency upon rough substrates (0.025 < P < 0.05) and appear to discriminate among surfaces of different rugosity. A weak photonegative response is shown at the time of attachment (P < 0.001). These responses result in an orientation which is in agreement with the position usually occupied by the scyphistoma in the field, i.e., inverted, and hence in a shaded location and on a firm, often rough or strongly contoured, surface.

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