Fig. 2

Comparison of the base of the two tentacle types - abundant secretory mucocytes and lack of cilia in the ecotoderm of ST compared to CT. Catch (a-d) and sweeper (e-h) tentacles sections are shown, respectively, stained with Alcian blue (a, f) and H&E (b-d, g-i). The endodermal layer (en) is wider than the ectodermal layer (ec), especially in the CT, with higher number of zooxanthellae symbionts (zo) in the CTs in comparison to the STs (compare a, b with f, g). Flagella (fl) can be observed on the endodermal layer of both tentacle types (c, h), facing the gastrovascular lumen. In contrast, ectodermal cilia (ci) are present only in catch tentacles (d) e, j Squash assays of the base area of catch and sweeper tentacles respectively, composed mainly from of holotrichous isorhiza nematocysts. Note here too the higher density of zooxanthellae in the CTs. Scale bars: a, b, f, g 20 μm; c, d, h, i 10 μm; e, j 25 μm