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Figure 9 | Frontiers in Zoology

Figure 9

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

Figure 9

The thick proximal base of the first branchial appendage (B1) after the fourth embryonic molt (stage 21). Limulus polyphemus, prone. Semi-thin section, LM. The thin distal end (*) of the appendage extends at left beyond the micrograph. This proximal base of the appendage is the source of the gill lamellae (GL). Their decreasing length toward the proximal end of the appendage (right) indicates their sequence of formation. The space between the lamellae is variable; an early gill lamella (GL') is very close to the preceding lamella. The central region of the appendage base has a band of muscle cells (Mu) and large vacuoles, probably from deteriorating cells. The gill lamellae have a thin outer wall of hypodermis and cuticle (Figure 7), and pillar-type trabeculae (T) are starting to form at intervals along the length of the lamellae. Scale, 130 μm.

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