Histochemical studies on the hyaline capsule of Holopedium gibberum Zaddach (Crustacea,Cladocera)

Summary The jelly capsule of the water flea Holopedium gibberum, was subjected to histochemical procedures for the visualization of acid mucopolysaccharides, amino acids, and proteins. The affinity of the capsule for azure A, alcian blue, colloidal iron, aldehyde fuchsin, and iron diamine reagents, at low pH, indicates the presence of a sulfated mucopolysaccharide. The presence of carboxyl groups, in addition, is indicated by alcian blue affinity in the combined aldehyde fuchsin-alcian blue and high-iron diamine-alcian blue procedures, as well as by the restoration of weak, but definite, basophilia after methylation-saponification pretreatment. The capsule remained alcianophilic in solutions of MgCl₂ as high as 0.4 molar. Cetylpyridinium blockade was removed by KCl solutions of 0.5–1.0 molar. The periodic acid-Schiff reaction was nil to very weak, in spite of extended oxidizing periods. None of the methods used for the visualization of amino acids or proteins gave unequivocally positive results. A possible origin of the capsular material is proposed.