. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 196 J. A. FREEMAN Apical Surface Area 1,14. VII VIII Instar Instar Figure 6. Development of the exopod. (A) E\opod in instar V limb. (B, C) Light and fluorescence images, respectively, of exopod in instar VIII, showing new setae and nuclei of GECs. Arrows in A and C indicate mitotic figures. (D) Exopod of adult, showing the setal region at the edge of the lobe. Nucleus (n) of a setal cell and an accessory cell (ac) are shown. Bars in A = 20 ^.m, B = 15 ^.m. C = 40 jim, D = 50 /urn. (E) Dimensions of the exopod during instars
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 196 J. A. FREEMAN Apical Surface Area 1,14. VII VIII Instar Instar Figure 6. Development of the exopod. (A) E\opod in instar V limb. (B, C) Light and fluorescence images, respectively, of exopod in instar VIII, showing new setae and nuclei of GECs. Arrows in A and C indicate mitotic figures. (D) Exopod of adult, showing the setal region at the edge of the lobe. Nucleus (n) of a setal cell and an accessory cell (ac) are shown. Bars in A = 20 ^.m, B = 15 ^.m. C = 40 jim, D = 50 /urn. (E) Dimensions of the exopod during instars V-VIII. Each bar indicates the mean ± 1 SD of 6-12 larvae. (F) Cell number and mean apical surface area for GECs in instars V-VIII. Numbers above the bars indicate the mean number and length of setae for those instars. Each bar represents the mean ± 1 SD of 5-12 limbs. with subsequent growth during late premolt (Freeman, 1991). or replication during mid-premolt that resulted in an undulated apical surface (Cheng and Chang, 1994). The results reported here reveal another process, expansion of the apical surface as the cell differentiates to a general epidermal cell (GEC) or a setal cell. These changes com- plement cell replication and are essential to growth and development of form in larval crustaceans. Of the four cell types studied, the GEC, setal, and transport cells contributed to growth as they differentiated. Another morphogenic force, evident in the transition from instar V to instar VI, involved a change in cell shape (SC in Table 1) from columnar to squamous, with minimum formation of new plasma membrane. It is possible that the elongation of the limb in the proximal-distal axis involved flattening of some of the GECs and a reorgani/ation of cell neighbors in the plane of the epithelium (Schock and Perrimon. 2002). The mechanisms by which these changes occur and new mem- brane is integrated into the plasma membrane remain to be studied. Each of the regions of the ph
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
