Synchronized measurements of head movement (as a proxy for nuchal retractor length) and muscle activation revealed that, while the MP nuchal retractor muscle
fibers were activated only for head retractions that occurred during escape jet locomotion, the MR fibers were activated 1) as the head retracted during escape jets and a few jets used during slow swimming, 2) during brief periods of head stasis as the animal changed swimming direction, and 3) during the rapid head extensions that followed an escape jet.
These cells were observed on both sides of the point of connection of the pedal retractor muscle
and foot (Fig.
ventral tip of anterior adductor- retractor muscle
scar is longer.
These conditions are clearly more reminiscent of the ancestral snail condition, with a single columellar muscle dividing into the various retractor muscle
elements some distance from its point of origin within a well-developed shell.
The penis retractor muscle
is attached to the mid-point of the right pedal retractor, as it does in Autocoptis eburate Thompson & Franz 1976, A argiphrix Thompson & Franz 1976, A.
This lengthening is usually performed by recession of the upper-lid retractor muscle
and repositioning these to weaken their action on the upper eyelid.
We previously identified cells with the morphology of neurons in the mesoglea of the pharynx and retractor muscle
; at least one cell in the mesoglea of the retractor muscle
was positive for expression of [alpha]238305 (Fig.
We found no muscle fibers other than those of the retractor muscle
posterior to the node in Cheliplana (Fig.
The following steps in larval development consisted in the formation of the retractor muscle
(stage 18) and the integumental attachment to the larval shell (stage 19) (Fig.
The fine structure of the contractile apparatus of the anterior byssus retractor muscle
of Mytilus edulis.
We present visual evidence of the lack of rigidity of the uncalcified larval shell in a basal trochid gastropod, Margarites pupillus (Gould), and provide photographic confirmation of our prediction that larval retractor muscle
contraction is insufficient to produce more than local deformation or dimpling at the site of muscle insertion.
The biologic zero point (BZP) of hybrid Pacific abalone Haliotis discus hannai (China) and Haliotis discus discus (Japan) at temperatures of 16[degrees]C, 20[degrees]C, and 22[degrees]C was calculated from the developmental hatching rate, formation of larval retractor muscle
, 90 degree torsion and formation of epipodial tentacles.