Fig. 1

Late auricularia of A. mollis. a Light microscope view of general anatomy of 14-day larva showing ciliated band (CB), stomach (ST), axohydrocoel (AX, position shown by *), left somatocoel (LS, position shown by *) and granular mass (GM). Scale bar 100 µm. b 14-day larva stained with Nile Red under blue light excitation and polarized light. Stomach fluoresces green; one of many red blastocoel spherules (BS) shown with white circle; granular mass (GM, position shown by *) also fluoresces red. Scale bar 100 µm. c 16-day auricularia stained with Nile Red under blue light excitation. Some blastocoel spherules (BS) are highlighted with white circles. Scale bar 200 µm. d 16-day auricularia stained with Nile Red under blue light excitation. Stomach (S) and blastocoelic spherule (arrow) carrying both neutral lipids (yellow) and more polar lipids (red). Scale bar 25 µm. e 16-day auricularia larvae stained with Nile Red and Hoechst nuclear stain under simultaneous blue light excitation and light microscopy. Stomach (S), left somatocoel (LS) and blastocoelic spherule (BS), with likely location of the nucleus (thin arrow). Black arrow indicates a cell of similar size to the BS that appears to differentiate from the stomach epithelium. White arrow indicates a smaller cell type lining the stomach epithelium. Scale bar: 25 µm. f Blastocoelic spherule within the blastocoel (Bl) of a 14-day larva stained with Nile Red under Nomarski light microscopy. Spherical inclusions (SI) in the blastocoelic spherule are indicated by arrow. Blastocoel also contains a fibroblast-type cell (Fb). Scale bar: 12.5 µm. g Blastocoelic spherule amoeboid movement in a 14-day auricularia larva stained with Nile Red under light microscopy. Arrows indicate sequence of movement of one blastocoelic spherule (white arrow, white circle) in a time lapse of 40 min. Scale bar: 50 µm