Opisth oteuthis calif orniana - — PEREYRA 
437 
or right, to the posterior, or down. But be- 
cause the ejection was feeble, it added only 
slightly to the net movement. Verrill (1896: 
74) and Berry (1952:184) were correct in 
stating that the siphon appeared to be too small 
to be used for efficient locomotion. 
The two dorsal fins, which heretofore had 
been considered as "inefficient looking” (Berry, 
1952:183), moved in a highly coordinated 
manner, augmenting the effect of the um- 
brella movement. (This is consistent with their 
morphology, inasmuch as they are supported 
by a cartilaginous rod and possess ample mus- 
culature. ) Balancing and orientation of the ani- 
mal were the main functions of the fins, but 
during certain phases of swimming they ap- 
peared to assist locomotion. 
When at rest the fins were positioned at 
the side of the head just behind the eyes in a 
down position, with the free-edge which con- 
tained the cartilaginous rod posterior (Fig. 3 a 
left). The fins could point slightly posteriorly 
but never anteriorly. 
Fin movement began with an up-stroke (Fig. 
3 a right). The supported posterior edge led on 
this stroke, resulting in the fin moving through 
the water with the least resistance (Fig. 3 d) . 
This stroke was terminated after the fin had 
moved upward almost 180° (Fig. 3e) . On the 
down-stroke the supported posterior edge again 
moved the fin, but this time the transverse axis 
was perpendicular to the direction of fin move- 
ment, offering the greatest surface area to come 
in contact with the water (Fig. 3c). Because 
of this, fin movement on the up-stroke was 
faster than on the down-stroke. This pattern 
of least resistance on the up-stroke and great- 
est on the down-stroke created an upward re- 
sultant force. Both fins were usually moved 
together in the same direction, but occasion- 
ally they were moved alternately, or one might 
be moved while the other was not. (Fig. 3b, f). 
Although the basic fin movement was always 
the same, the axis of movement could be shifted 
90° forward from the up-down to an anterior- 
posterior direction or to any degree between 
these extremes. The greatest surface area of the 
fin was exposed on the posterior or down- 
stroke. This permitted net movement in any 
direction from upward to forward or anterior. 
Thus, by moving the fins alternately or together, 
and by adjusting the axis of movement and the 
strength of the stroke, the animal had consid- 
erable control over the direction of movement 
created by the powerful undulations of the 
umbrella. The animal might swim up, side- 
ways, or down depending on its attitude at the 
time of the umbrella closing. 
The tempo of fin movement was always 
greater than that of umbrella movement. Usu- 
ally it was in the ratio of three fin strokes to 
every umbrella stroke, but this varied. Also, 
the fin movement was coordinated so that a 
down-stroke coincided with the closing of the 
umbrella. 
When the animal was at rest on the bottom, 
fin movement usually continued, but at a 
slower rate and in various directions. Also, the 
pattern of fin movement was generally alternate. 
As the swimming undulations of the um- 
brella ceased and the animal settled to the bot- 
tom, the tempo of fin movement increased con- 
siderably in an alternate pattern. This increased 
fin activity probably helped to slow the ani- 
mal’s descent and provided for better attitude 
control. 
The alternate fin movement pattern was sur- 
prising. Considering that both fins are sup- 
ported by a common cartilaginous rod, this rod 
must be able to undergo considerable torsion 
for the fins to be moved alternately. 
The use of photofloods to take pictures re- 
vealed a negative light reaction. Prior to turn- 
ing on the photofloods, the animals actively 
moved in the aquarium under subdued light. 
When the photofloods were turned on, activity 
continued for 15 to 20 seconds and then all 
movement ceased. As long as the photofloods 
were on, the animal remained perfectly still. 
Several authors have hinted at the existence 
of the pulsating locomotory pattern from 
knowledge of the gross morphology of the 
species. Ijima and Ikeda (1895:328) stated 
. . that alternate closure and expansion of the 
arms is of much greater moment to Opistho- 
teuthis than to most other Cephalopods, since 
the ejection of water from the comparatively 
small branchial chamber and siphon must be of 
subordinate significance.” Berry (1952:184) 
offered similar speculations, stating that the 
