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Figure 7 | Frontiers in Zoology

Figure 7

From: Development and epithelial organisation of muscle cells in the sea anemone Nematostella vectensis

Figure 7

Development of columnar longitudinal muscles in primary polyps and juveniles. A Early primary polyp (~5 d), overview. B Detail of A. Cells located next to each other at the base of the mesentery increasingly accumulate myofilaments (black arrows) in their basal part. C Detail of A. Some retractor muscle cells (long black arrows) start to constrict the basal from the apical part of the cell, leaving behind thin cytoplasmic bridges (short black arrows), while in some the nucleus still lies near the myoneme (short white arrow). D Detail of A. Secondary mesentery. E Detail of D. As in primary mesenteries more cells accumulate myofilaments (black arrows) at their bases. F Detail of D. In the secondary mesenteries, myonemes (black arrows) are still located at the tip of the mesentery, but are more pronounced on one side. G Juvenile (~3 months) polyp, overview. H Detail of G. Despite the constriction of the myoneme, parietal muscle cells retain an epithelial organization (single cell highlighted in red). Inlet: Arrangement of myofilaments and adherens junctions between myonemes. I Detail of G. In the retractor muscle the sheet of myonemes starts to fold. Muscle cells are still epithelial (single cell highlighted in red). Inlet: Arrangement of myofilaments and adherens junctions between myonemes. J Optical cross-section of a mid-planula. The orientation of the retractor muscle is species-specific and predetermined for every mesentery. This allows predicting the future side of the retractor muscle in all mesenteries, as soon as all mesenteries have emerged. Red arrows: primary mesenteries, white arrows: secondary mesenteries. ec, ectoderm; en, endoderm; gc, gastric cavity; pb, proximal bulge; pm, primary mesentery; sm, secondary mesentery; mf, mesenterial filament, myo, myoneme; np, neural plexus; nu, nucleus. Scale: A, G: 50 μm; B, C: 2 μm; D, H, I: 5 μm, E: 500 nm; F: 1 μm.

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