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Differences in ion regulation in the sea urchins Lytechinus variegatus and Arbacia lixula (Echinodermata: Echinoidea)
Vidolin, D.; Santos-Gouvea, I.A.; Freire, C.A. (2007). Differences in ion regulation in the sea urchins Lytechinus variegatus and Arbacia lixula (Echinodermata: Echinoidea). J. Mar. Biol. Ass. U.K. 87(3): 769-775.
In: Journal of the Marine Biological Association of the United Kingdom. Cambridge University Press/Marine Biological Association of the United Kingdom: Cambridge. ISSN 0025-3154, more
Peer reviewed article  

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  • Vidolin, D.
  • Santos-Gouvea, I.A.
  • Freire, C.A.

    The regular sea urchin Lytechinus variegatus, a species previously reported from areas of reduced salinities, and Arbacia lixula, a species unreported from diluted waters, were submitted to seawater dilution or seawater dilution in magnesium-supplemented waters. Seawater (35 psu) was either proportionally diluted with filtered dechlorinated tap water (30 psu, 25 psu), or diluted and supplemented with magnesium as MgCl2 (30+Mg, 25+Mg), up to full-strength seawater Mg2+ levels (35 psu, ~54 mM Mg2+ ). Magnesium supplementation was intended to verify the interfering effect of magnesium on osmo-ionic concentrations of the coelomic fluid (CF) of two ecologically distinct species of sea urchins. After 6 h in control (35 psu) or experimental seawater, CF samples were withdrawn by puncturing through the peristomial membrane. Coelomic fluid osmolality ([Osm]), and concentrations of ([Na+]), ([Cl-]), ([Mg2+ ]) and ([K +]) were measured for both species. Under all conditions, L. variegatus displayed higher CF osmolality, [Na+], and [K+] values than the water (and A. lixula). Comparatively, L. variegatus is designated as a'hyper-conformer', while A. lixula is an 'iso-conformer'. The CF [Mg2+ ] showed no evidence of being controlled by either species. Mg2+ supplementation in diluted seawater affected Mg2+ and Cl- levels only. Na+ appears to be taken up actively by L. variegatus, rendering its CF mostly hyper-ionic for Na+ (and hyperosmotic) relative to external seawater. The different gradients observed with the different ions suggest selective permeabilities or ion regulation by L. variegatus.

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