The Antennular Activities of the Hermit Crab, Pagurus Alaskensis (Benedict)

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Abstract
1. The antennular activities of the hermit crab, Pagurus alaskensis, were studied with the aid of motion pictures taken at speeds of 50, 200 and 400 frames/sec. 2. Most movements of the antennule represent one of four types of antennular activity: flicking, rotation, wiping and withdrawal. These activities are described in detail. 3. Water resistance forces contribute to the timing and duration of some antennular movements. 4. Flicking occurs non-rhythmically and flicks of the left and right antennules and never synchronized. The factors which influence the mean frequency of flicking are discussed. 5. The timing of joint movements during a flick, and the morphology of the outer flagellum and the aesthetasc hairs, appear to be adapted to facilitate splaying of the aesthetascs. It is proposed that this splaying might facilitate the chemoreceptive process by circulating water around the aesthetasc hairs. 6. During antennular wiping the endopodites of the 3rd maxillipeds are used to remove debris caught amongst the aesthetasc hairs. Light mechanical stimulation of the aesthetascs is sufficient to elicit wiping. 7. The antennules are reflexively withdrawn from certain stimuli either by extension or by slow or fast flexion. The functional significance of the withdrawal reflexes are discussed in relation to the stimuli involved and the form of the reflexes. 8. Continued application of certain stimuli to the antennules, eyestalks, antennae or body results in tonic flexion withdrawal which involves postural modifications of the antennules, eyestalks and antennae.