californica is the red algal chloroplast (or rhodoplast), which is catabolised in digestive vacuoles in a specialized cell type, the rhodoplast digestive cell, in the animal's digestive gland.
The presence of rhodoplast digestive cells appears, therefore, to be necessary for the production of colored ink in A.
Rhodoplast digestive cells were found in the digestive glands of all species studied (Figures 1(a), 1(d), 1(e), 1(g), and 1(h)).
The appearance and diameter of the phycobilisome sized particles (Figure 1(c)) in rhodoplast digestive cell vacuoles of D.
Aplysia juliana had large pitted electron dense granules in cells adjacent to rhodoplast digestive cells (Figure 1(b)).
The inability to produce colored ink by several species of sea hare could be due to several factors: (1) the absence of the rhodoplast digestive cell type in the digestive gland (this is the principal cell involved with red algal chloroplast digestion and modification of its pigment [12,13,16]); (2) the development in some sea hares of rhodoplast digestive cells only when feeding on red algae; (3) a diet preference that is deficient in red algae and its pigment; and, finally, (4) ink glands that are incapable of ink production regardless of rhodoplast digestive cell presence or the algal diet of the sea hare.
dolabrifera did not, therefore, appear to be due to either the absence of rhodoplast digestive cells in the digestive gland or a lack of rhodoplasts in their digestive vacuoles.
Dolabrifera dolabrifera does not produce colored ink even though rhodoplast digestive cells were present in its digestive gland and appeared to be involved in the digestion of rhodoplasts.
But abundant rhodoplast digestive cells with rhodoplasts in various stages of digestion were seen in the digestive gland of D.
dolabrifera might also be due to an ink gland that cannot form ink regardless of diet or the presence of functional rhodoplast digestive cells in the digestive gland.
juliana when this sea hare is restricted to a red algal diet did not involve the reappearance of rhodoplast cells in the digestive gland; they were always present.
Presence of Rhodoplast Digestive Cells in Sea Hare Digestive Glands.