. The Biological bulletin. Biology; Zoology; Marine biology. LOCOMOTION IN MELAMPUS 309 r 4 PM RAPM B LACM. Figure 2. Relationship between columellar muscles and the foot in Melampus. A, view of animal's left side; B, right side. Left anterior cephalic muscle (LACM) is unshaded, the right anterior and right and left posterior muscle (RAPM) stippled, and buccal muscle (B) crosshatched. the columellar muscles attached to the inner wall of the shell (Morton, 1955). The muscles follow the inner surface of the shell within the body whorl in approxi- mately a 360° turn from origin to insertion in th
. The Biological bulletin. Biology; Zoology; Marine biology. LOCOMOTION IN MELAMPUS 309 r 4 PM RAPM B LACM. Figure 2. Relationship between columellar muscles and the foot in Melampus. A, view of animal's left side; B, right side. Left anterior cephalic muscle (LACM) is unshaded, the right anterior and right and left posterior muscle (RAPM) stippled, and buccal muscle (B) crosshatched. the columellar muscles attached to the inner wall of the shell (Morton, 1955). The muscles follow the inner surface of the shell within the body whorl in approxi- mately a 360° turn from origin to insertion in the extended foot. In addition to the buccal retractor muscle, two major subdivisions of the columellar muscle are apparent in Melampus. The left anterior and cephalic muscle (LACM, Fig. 2) originates in several adjacent bundles and further subdivides into muscle bands that insert around the head, into the left tentacle and oral veil, the left side of the propodium and approximately the anterior third of the left side of the metapodium. The right anterior and right and left posterior muscle (RAPM, Fig. 2) has a single origin on the shell and divides into muscle bands that insert on the right tentacle, the right oral veil, the right propodium, the anterior portion of the metapodium and bilaterally in the posterior region of the metapodium. Thus the muscles enter the foot in a quite asymmetrical pattern with those muscles on the left side that support the shell being the more massive. The columellar muscle system of Melampus probably includes both the longitudinal and columellar muscle groups described for Lymnaea by Plesch, Janse and Boer (1975). In serial sections of snails quick-frozen in the act of crawling, there is no evidence that intrinsic bands of muscle fibers form discrete layers above the sole of the foot. Rather, the fibers that could be traced appear to be derived from columel- lar muscles. This is apparent in the parasagittal section which cuts through the left ante
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