Assertion: seahorse's gill opening | /r/HasProperty | single
Facets:
Source sentences:
text: Apart from their extremely small size, they have a single gill opening on the back of the head (all other seahorses have a pair of gill openings either side of the head) and the young are brooded within the male’s trunk rather than a pouch on the tail.
text: Unlike other seahorses, they have a single gill opening on the back of the head, instead of two on the sides.