Two or three millimetres long and indistinguishable from the algae it sits in without magnification.
Five or six millimetres, rarely as much as a centimetre — small enough that most people are shown it rather than find it. The body and every appendage carry long branched setae that trap detritus and filamentous algae, so the animal looks like a moving scrap of turf, and the colour follows the substrate: green, red, brown, cream or mottled. The characters that formally diagnose it — the shape of the rostrum, the armature of the claws, the divisions of the wrist — are not visible on a diving photograph, which means in practice divers identify it by overall impression. That is worth saying plainly, because it is exactly the situation in which cryptic species go unnoticed.
No host: it lives on filamentous algal turf, hydroids, sponge and rubble in shallow water, which is a habitat rather than a symbiosis. It is almost stationary, and the usual giveaway is a hop or a short backward flick when something disturbs it. It rocks gently with the surge, which is what makes it findable and what makes it very difficult to photograph. It grazes algae, detritus and small plankton. Indo-West Pacific, from around 3 to 25 m on typical dives; the formal distribution records are too sparse to say more than that.
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.