Ideas:

1. Given that this type of glyph

is showing vai-ora-a-Tane, it seems reasonable to assume that the person in the glyph above is holding a container of water in his left hand. (Metoro also often used the word vai in connection with this type of glyph.)

2. Though the general form of these two (presumed) containers of water are somewhat similar, the glyph with 'fins' has a canoe-shape, while the one without 'fins' is more like an egg, perhaps showing that a new month will soon be born.

3. In the (possible) Moon calendar in this text of Keiti there are 8 more glyphs of this type, which, however, have one or more additional signs.