Banded tail, spiny body, and it comes out on the sponges after dark.
A seahorse to about 18 cm, more angular and more strongly spined than the common seahorse, usually black, brown or deep yellow, and identified by the tail, which carries clean alternating dark and pale bands along its length. Yellow animals with a black-banded tail are unmistakable; dark ones need the tail looked at. The species is listed as Vulnerable and, like all seahorses, is on CITES Appendix II.
Nocturnal to a degree that most of its relatives are not. Through the day it is wedged low in sponge, weed or rubble and is very hard to find; after dark it climbs and perches in the open on sponges and gorgonians, and a night dive on the right slope will produce several. Males brood in a closed pouch. Recorded from about 3 to 20 m. Because it is found at night with a torch, the temptation to hold a light on one while the diver sets up is strong; a seahorse will turn its head away from a continuous beam, so a focus light kept dim and off the face costs nothing and gets a better animal.
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.