Observations on luminescence in sea pens (Pennatulacea)

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Abstract
The luminescent responses of sea pens (Leioptilus gurneyi) have been studied by visual observation and photo-electric recording. Light is emitted by the polyps (autozooids and siphonozooids) when the animal is excited. Gentle mechanical stimulation and electrical stimulation (condenser shocks) evoke luminescent waves which pass over the rachis at a velocity of 26.4 cm/s (20.5 degrees C). The first luminescent wave appears after 1 to 3 shocks, depending on the condition of the animal. Subsequently, waves arise at the rate of 1/shock, and increase progressively in intensity owing to neuroeffector facilitation. On recording from restricted loci (width 2 cm), the following data for temporal characteristics of flashes (from autozooids) were obtained: latent period, 0.18s; total duration of flash, 1 to 1.2s; maximal intensity from first deflexion, 0.2s; time to half-maximum, 0.1 s. Strong mechanical and prolonged electrical stimulation produce a refractory state in which the animal contracts and no longer produces luminescent waves. Slow progressive spread of luminescence can then be induced by maintained repetitive stimulation. This effect is ascribed to internuncial facilitation overcoming fatigue in the nerve net. Certain lines of evidence indicate that light may temporarily inhibit luminescence, apparently by affecting the excitatory system. The results are related to observations made on the luminescent responses of other sea pens.

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