(a) Periodic acid-Schiff (PAS)-stained histological sections through the intestine of stage 32 red stingray embryos. Faecal matter (*) accumulated in the posterior half of the intestine. (b) The fifth row of spiral valve (left) and its close-up view (right). (c) The 17th row of the spiral valve (left) and its close-up view (right). (d) The posterior end of the intestine and its close-up view. Densely distributed PAS-positive goblet cells (white triangles) are seen in the right panels in c and d. Scale bars =100 µm in left panels of b-d; 10 µm in right panels of b-d.