Matches Halimeda algae so closely it is usually found by moving the algae, not by seeing the fish.
The smallest of the ghost pipefish, around 5 to 6.5 cm depending on which measure is quoted, and the one whose name causes the most trouble. The identifying character is the caudal peduncle, two to three times as long as it is deep — intermediate between the almost absent peduncle of the robust ghost pipefish and the long stalk of the ornate — combined with small, rounded, short fins and a truncate tail. Its dermal appendages are branched rather than the long simple filaments of the ornate. Living fish are usually pale green with lighter mottling and a large black blotch on the membrane between the first two dorsal spines. Say it plainly, because it is the commonest error on this animal: green does not mean halimeda, and halimeda is not always green. All of them take the colour of their surroundings, and a green robust ghost pipefish in a seagrass bed is a robust ghost pipefish.
Found among Halimeda and coralline algae, which it resembles closely — the segmented calcified plates of the alga and the fish’s flattened, mottled body are a good match. Described only in 2002, from material from the Maldives, Western Australia, Papua New Guinea and the Marianas. Recorded between about 15 and 30 m. Brooding, hatching and the pelagic larval phase are as for the rest of the family.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.