Octopus Movement: Push Right, Go Left Scott L. Hooper  Current Biology  Volume 25, Issue 9, Pages R366-R368 (May 2015) DOI: 10.1016/j.cub.2015.02.066 Copyright © 2015 Elsevier Ltd Terms and Conditions

Figure 1 Octopuses move by their arms pushing the body in the desired movement direction. (A) The proximal portion of arm 5 has shortened — the lines in each arm represent arm suckers; shortening shown by the lines in the proximal portion of arm 5 being closer together than in the other arms — and the suckers at the distal end of the shortened portion (black rectangle in arm) have attached to the substrate. Open arrows show direction of body movement that occurs when shortened region elongates. Distal portion of arm (red) does not move when proximal portion elongates (dashed and solid arrows in A and B show that this portion of the arm remains in a constant position relative to the environment, represented by the rectangular surrounds). (B) Octopus position after elongation of proximal portion of arm 5: animal has moved up and left. During elongation, velocities of the attached suckers and the distal portion of the arm are zero, and distances to the mouth for both increase in parallel as elongation proceeds (see Figure S2A in [1]). (C) Data in red show behaviorally observed percentage of movements in directions indicated by each point. Data in blue show percentage of movements in these directions predicted from frequencies with which different pairs of arms are co-activated. (Behavioral data from Figure 1C, arm activation data from Table S1, of [1]). Data are symmetrical around the 0°–180° axis because in [1] the behavioral data from positive and negative directions were combined by taking the absolute value of the angles (that is, all movements from –30° to +30° were reported in a 0° to +30° bin). I therefore also performed this treatment on the arm activation data. To produce the plot the percentages in each absolute value bin were divided by two and this value plotted at the appropriate positive and negative angle values (for example, the 15.9% of the behavioral data that occurred between angles of –30° to +30° were plotted as 7.95% at ±15°). Current Biology 2015 25, R366-R368DOI: (10.1016/j.cub.2015.02.066) Copyright © 2015 Elsevier Ltd Terms and Conditions