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Figure 15 | Frontiers in Zoology

Figure 15

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

Figure 15

Cluster of cuticular vesicles (CV) at the tip of the genital operculum after the third embryonic molt (stage 20). Limulus polyphemus, prone. TEM. The cuticular wall of these vesicles encloses plasma membrane and particles like that of nearby hypodermal cells (C), suggesting the vesicles are released from these cells at the appendage tip. One vesicle (CV') is attached to the cuticular tip as though it is in the process of release or uptake. Invaginations like those evident here (*) and a small cluster or cuticular vesicles are commonly seen at the tips of the genital operculum and first branchial appendage after the third molt (Figure 2A), but such vesicles were not seen in later stages. The vesicles appear to be held in place by a thin, transparent membrane (Me), probably the exuvium not yet removed from the appendages after the third molt. The cuticle (Cu) of the appendage tip is layered and much thicker than that of the vesicles as though they were released at an earlier time of development. Scale, 2 μm.

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