. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MB. Figured. Computer-assisted reconstructions of transversely sectioned larvae at three stages of develop- ment (protoconch not included I. The upper row shows reconstructions of whole larvae (all viewed from the definitive left lateral side of the visceral lobe) at postfertilization times of 52 hours (A), 5 days (D). and 9 days(G). The middle row (B. E. H) shows the same three stages with the anterior portion omitted and with profiles of the larval retractor muscle (LRM) and accessory larval refractor muscle (ACC) superimp
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MB. Figured. Computer-assisted reconstructions of transversely sectioned larvae at three stages of develop- ment (protoconch not included I. The upper row shows reconstructions of whole larvae (all viewed from the definitive left lateral side of the visceral lobe) at postfertilization times of 52 hours (A), 5 days (D). and 9 days(G). The middle row (B. E. H) shows the same three stages with the anterior portion omitted and with profiles of the larval retractor muscle (LRM) and accessory larval refractor muscle (ACC) superimposed on the body wall profiles. The lower row (C, F, I) shows the same reconstructions with superimposed muscle profiles, but viewed from the anterior end of the larvae. Asterisk in (B) and (C) indicates the oblique tract of the LRM at 52 hours: arrowhead in (F) indicates the U-shaped excavation in the LRM where it partialK surrounds the esophagus. The ACC is stippled in B, C. E, and F; the mantle branch (MB) of the LRM is stippled in H and I. Other abbreviations: F = foot: MC = mantle cavity; MF = mantle fold: V = velum: VL = visceral lobe. vae. the attachment plaque of the LRM has not acquired the ultrastructural characteristics of its fully differenti- ated state, as shown in Figure 2, hut whole mounts of live larvae suggest that epithelial cells of the future LRM attachment plaque are nevertheless fastened to the inner wall of the shell at this stage (Fig. 5). The attachment site is located at the bottom of the protoconch, but is offset toward one side. The offset is right-sided with respect to the prerotated cephalopodium, but becomes left-sided with respect to the postrotated cephalopodium (Fig. 4: compare A-C with D-F). The two largest myocytes of the LRM at 52 hours have different distal trajectories. One continues anteriorly along the right side of the foregut and is accompanied by four smaller LRM myocytes. The other of the two largest myocytes bends abruptly to the l
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
