Lives only on Muricella sea fans, matching the host's colour and tubercles.
Up to about 24 mm and mature from 13, with 11 or 12 trunk rings and 31 to 34 tail rings. The snout is extremely short with a bulbous tip, the head sits at close to a right angle to the body, and the coronet is a rounded knob without spines. The identifying feature is the ornament: irregular bulbous tubercles, not spines, over a body so fleshy that the bony rings are hidden. Structurally it shares with Denise’s pygmy seahorse a reduced skeleton — no distinct coronet, no raised cleithral ring, and the ventral trunk ridges incompletely ossified into star-shaped plates — which separates that pair from every free-living pygmy. In the water, though, the practical distinction from Denise’s is simpler: this one is knobbly and stout on a bushy fan; that one is smooth, thin and usually orange.
Obligate on gorgonians of the genus Muricella, and the two colour forms track the host — pale grey and purple with pink tubercles on one, yellow with orange on another. A 2023 record from Japan on an Anthogorgia is the first host outside the genus. Density runs around one animal per 600 m² of reef, with only about one fan in five occupied. Gestation is exactly fourteen days; broods of a dozen to sixty-five; young are born at about 6.5 mm and settle after two to three weeks at around 12 mm. The colour is acquired, not inherited — settlers take on the colour of whatever host they choose within about seventy-two hours, and orange parents have produced pink young. Adults have been followed on one fan for up to forty weeks and movement between fans has never been observed, though nobody has run a mark-recapture study to test it. Recorded from about 16 to 60 m. On strobes: the one controlled study exposed a full-sized seahorse to some 4,600 flashes over 34 days and found no retinal damage and no change in feeding. It was not a pygmy, the animals could not swim away, and nobody has tested a species that cannot leave its host — so limiting strobes here is a reasonable precaution rather than a demonstrated need. What the same study did show clearly is that handling the animals, and by extension handling the fan, causes real stress.
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.