ZOOLOGY: a H. PARKER 
449 
LOCOMOTION OF SEA-ANEMONES 
By G. H. Parker 
ZOOLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT 
HARVARD COLLEGE 
Received by the Academy, June 15, 1916 
Although sea-anemones belong to a group of animals characterised 
by radial symmetry, they have long been known to exhibit a bilateral 
arrangement in their mesenteries and adjacent parts. Most bilateral 
animals move in definite relations to their axis of symmetry. Is this 
true of sea-anemones? 
Single specimens of Actinia or of Sagartia will creep now in the di- 
rection of their planes of symmetry, now at any angle to those planes 
and thus demonstrate the entire independence of the direction of loco- 
motion and the axis of symmetry. This is especially clearly seen in 
Sagartia which will creep away from a source of light irrespective of the 
relation momentarily called forth between the direction of locomotion 
and the animal's structural axis. Locomotion in sea-anemones is there- 
fore a radial operation performed by the radial pedal disc and not 
necessarily associated with the more or less bilateral oral disc. 
Locomotion is accomplished by a wave-like movement that progresses 
over the pedal disc in the direction of locomotion. In a specimen of 
Sagartia with a pedal disc of about 4 mm. diameter, the locomotor wave 
coursed over the disc in an average time of 1.65 minutes and with each 
wave the animal progressed on the average 1.2 mm. In a large sea- 
anemone, Condylactis, with a pedal disc 130 by 80 mm. the passage of a 
locomotor wave required on the average three minutes and the animal 
progressed for each wave on the average 11.4 mm. 
In the locomotion of sea-anemones each part of the pedal disc is 
successively raised from the substratum, moved forward, and put down. 
The attachment to the substratum is due chiefly to adhesion heightened 
by the secretion of a thick slime rather than to a sucker-like action 
of the pedal disc. The mechanism of locomotion consists of the circular 
muscle of the pedal disc, the basilar muscles, and the longitudinal 
muscles of the mesenteries all of which act on the fluid-filled spaces in 
the pedal region. The pressure thus generated is not above 6 cm. of 
water. 
Specimens of Sagartia from which the oral disc has been cut off will 
creep in an essentially norm^al manner, for instance, away from a source 
of light. Hence the pedal portion of a sea-anemone, like its tentacles. 
