Many symbiotic algae are observed in the apical part of <i>Chlorohydra viridissima</i> endodermal digestive cells following feeding with <i>Artemia</i>.

<p>The symbiotic algae can be seen as small (∼10 µm) green spheres, and those found in the apical part of the cells are marked by arrowheads. A) Unfed <i>Chlorohydra</i>; B) <i>Chlorohydra</i> 15 minutes after feeding; C) <i>Chlorohydra</i> 5 hours after feeding. en = endoderm, ec = ectoderm, gvc = gastrovascular cavity, art = artemia. The dashed line between the endoderm and the mesoderm denotes the mesoglea. Bar = 50 µm. D) A quantitative analysis of the number of symbiotic algae in the apical third of the endoderm, at different times after feeding. Values and error bars represent averages and SE from 4–6 animals. There number of symbionts in the apical part of the cell was weakly affected by time (ANOVA, F = 5.067, p = 0.025) and time by treatment (F = 4.267, p = 0.04) but strongly affected by the treatment (F = 26.667, p<0.001). The difference between the fed and unfed animals is highly significant 15 minutes after feeding (Student's two-tailed t-test, p = 0.0048, represented by * in the figure), and is not significant at other time points. E) Reduction in the number of algal symbionts per endodermal cell in fed compared to unfed animals, 15 minutes after feeding. Values and error bars represent averages and SE from 30 endodermal cells per time point. The number of symbionts was not affected by time (ANOVA, F = 0.438, p = 0.781), and the effect of treatment was marginally significant (F = 3.76, p = 0.053). There was a significant difference between fed and unfed animals after 15 minutes (Student's two tailed t-test, t = 2.686, p = 0.009, represented by * in the figure) but this difference was not significant at other time points.