How do male pipefishes carry developing eggs?

In the order Gasterosteiformes, male pipefishes are responsible for carrying fertilized eggs until they hatch. Contrary to the assumption that all pipefishes use a pouch, the method of carrying eggs varies by species.12

Male pipefishes carry developing eggs in the following ways:

• External attachment: Eggs may be glued directly to the ventral (under) surface of the male’s body or tail.12
• Embedded: Eggs may be embedded within a spongy area on the male's body.1
• Brood pouches: Eggs may be carried within specialized structures that offer varying degrees of protection. These range from simple skin folds or "zip-front" enclosures to fully formed cavities similar to those found in sea horses.21

It is important to note that this behavior is distinct from some other members of the order, such as certain ghost pipefishes, where the female carries the eggs in a pouch formed by her pelvic fins.2