Think of hauriant with the fish curved in an arc with the bend to the right. A common posture for carnivorous beasts and monsters. Rare in period. A common posture for non-carnivorous beasts. Less common than passant.
Sejant beast is seated with forelegs down and together.
Tail is up by default if the beast has a tail. Sejant Erect beast is seated, but has forelegs off ground as if attacking. The tail curls under the body of the animal and emerges just ahead of the haunches then rises above the back. Appears to be rare in period, except for a few animals, such as the dog and the stag. If the beast has a tail it is down and coiled around the animal.