Figure 6

Early gill lamellae starting to develop from the posterior surface of the first branchial appendage (B1) after the third embryonic molt (stage 20). Limulus polyphemus, prone. TEM. The lamella at this early stage of development is not yet organized into an outer hypodermis and central lumen as evident later in Figure 7. Some peripheral cells (C) appear to be intact as though they could become part of a hypodermal layer. Cell debris (CD) at the center and base of the lamella suggests the beginning formation of a lumen. The lamella has a very thin external cuticle (Cu) at this stage. Cl, narrow cleft (Figures 2B, 3, 5) between the bases of the first and second branchial appendages; GH, granular hemocyte [29–31]. Scale, 10 μm.