. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HATCHING ENVELOPE ASSEMBLY IN LOW SODIUM 91. Figures 16-19. A series of TEM micrographs showing effects of various substitutions on HE formation. Arrowheads = HE; PVS = perivitelline space. Bar = 0.5 ^m for all. Figure 16. A Trachypenaeus similia egg at 60 min showing the fluffy appearance of an incomplete HE in ChCl-substituted seawater. Figure 17. A Sicyonia ingentis egg at 70 min showing the fluffy appearance of an incomplete HE in ChCl-substituted seawater. Figure 18. A S. inffcniis egg at 60 in Tris-substituted seawater

- Image ID: RHMXRT
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HATCHING ENVELOPE ASSEMBLY IN LOW SODIUM 91. Figures 16-19. A series of TEM micrographs showing effects of various substitutions on HE formation. Arrowheads = HE; PVS = perivitelline space. Bar = 0.5 ^m for all. Figure 16. A Trachypenaeus similia egg at 60 min showing the fluffy appearance of an incomplete HE in ChCl-substituted seawater. Figure 17. A Sicyonia ingentis egg at 70 min showing the fluffy appearance of an incomplete HE in ChCl-substituted seawater. Figure 18. A S. inffcniis egg at 60 in Tris-substituted seawater
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Image ID: RHMXRT
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HATCHING ENVELOPE ASSEMBLY IN LOW SODIUM 91. Figures 16-19. A series of TEM micrographs showing effects of various substitutions on HE formation. Arrowheads = HE; PVS = perivitelline space. Bar = 0.5 ^m for all. Figure 16. A Trachypenaeus similia egg at 60 min showing the fluffy appearance of an incomplete HE in ChCl-substituted seawater. Figure 17. A Sicyonia ingentis egg at 70 min showing the fluffy appearance of an incomplete HE in ChCl-substituted seawater. Figure 18. A S. inffcniis egg at 60 in Tris-substituted seawater. Note the ring vesicles (arrows) in the peripheral cytoplasm. HEs were not detected in any samples. Figure 19. A S ingenlis egg at 60 min in KCI-substituted seawater. The morphology for these HEs appears normal. Particularly notable are two dramatic and distinct extra- cellular events resulting in the assembly of new coats around the egg (Clark el al. 1980, 1990; Lynn and Clark. 1987; Filial and Clark, 1988). The results reported here are the first to demonstrate a role for sodium in the ele- vation or hardening of the hatching envelope in the pen- aeoidean shrimp species T. similisandS. ingentis. Sodium can be replaced by potassium but not by Tris or choline, classic substitutes for sodium (e.g.. Chambers and De Ar- mendi, 1979; Schuel el al, 1982). The major effect on the morphology of the HE related to the deficiency of sodium appeared to be the incomplete transformation of the nascent envelope into a definitive bilayered pattern. Particularly interesting is the fact that both of these pen- aeoid species show a similar dependence on the presence of sodium ions for the assembly of the HE. A sodium dependency is also observed in the elevation and hardening of the sea urchin fertilization envelope (FE) (Nishioka and Cross, 1978; Schon and Decker, 1981; Schuel elal, 1982; Schuel, 1985; Cheng el al, 1991). The HE of the shrimp and the FE of the sea urchin are similar in that the

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