This creature is unusual among the miroglyphs of rongorongo. But the location in Monday, just before a glyph indicating a time period (the period of Waxing Moon in this instance), makes one think about the writer trying to tell something about this period of time.

I suggest that we should read this sign as telling us about the relation between the week and the month.

The 'arms' of the creature divide the glyph more or less in the middle and my suggestion is that we here should see the division of the period of Waxing Moon (respectively Waning Moon two glyphs later) into two weeks.