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Figure 1 | Frontiers in Zoology

Figure 1

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

Figure 1

Ventral view of embryos of the horseshoe crab. Limulus polyphemus , supine. SEMs. A. After the second embryonic molt (stage 19), the prosomal legs (L1-L4) are prominent, tapered and starting to become segmented, while the opisthosoma only has bilateral ridges in each segment (1-4). The development of the chelicerae (Ch) and pedipalps (Pd) are unusually delayed in this specimen. M, mouth. Scale, 500 μm. B. After the third embryonic molt (stage 20), the first opisthosomal segment has small bilateral lobes, the future chilaria (Ch). In the following three opisthosomal segments, the genital operculum (GO) and first (B1) and second (B2) branchial appendages are bilateral flap-like structures with small median (Me) and large lateral (La) lobes. These appendages are all immobile at this stage. Barely discernible are primordial gill lamellae (asterisks) from the posterior surface of the first branchial appendage. Gp, gonopore. Scale, 120 μm.

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