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Figure 5 | Frontiers in Zoology

Figure 5

From: Ultrastructure of book gill development in embryos and first instars of the horseshoe crab Limulus polyphemus L. (Chelicerata, Xiphosura)

Figure 5

Two gill lamellae (GL) starting to develop from the posterior surface of the thick, proximal base of the first branchial appendage (B1) after the third embryonic molt (stage 20). Limulus polyphemus, prone. Semi-thin section, LM. The outward growth of the hypodermal cells gives these appendages a knobby appearance as described above (Figures 2A, B and 3, 4). The gill lamellae at this early stage of development are not yet organized into an external hypodermis and central lumen (Figures 6, 7). A narrow cleft (Cl) is evident between the bases of the first and second (B2) branchial appendages. L, lumen. Scale, 45 μm.

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