Pontonia pinnophylax
A rare find inside fan mussels off La Palma, Canary Islands, in cool 17 to 23C water. Look close, this one hides deep.
A small, semi-transparent shrimp with a pale pinkish or amber tint that lets it blend almost invisibly against the mantle tissue of its host fan mussel. Its body is smooth and slightly flattened, built to sit tucked inside a bivalve shell rather than swim openly over the reef. You will not spot this one by scanning open sand or rock; you spot it by finding the host first and then peering into the gap between the valves.
Found living inside the mantle cavity of fan mussels (Pinna species), rarely if ever seen out in the open water column. Divers who log it do so by carefully checking known fan mussel shells rather than by spotting movement on the reef, since the shrimp stays put with its host and reacts to disturbance by retreating deeper into the shell. Expect stillness rather than any active swimming display.
This shrimp lives its whole adult life as a guest inside a single fan mussel, a relationship called obligate symbiosis, feeding on food particles and mucus the host filters from the water rather than foraging independently.
There is not enough seasonal data to call a peak period, so treat it as a year-round possibility within its observed 17.4 to 23.4C water temperature range. Cooler months on the lower end of that range appear just as viable as warmer ones based on current records.
Every logged sighting so far comes from the Canary Islands, specifically La Palma, making it the only region currently confirmed for this species. If you are hunting for it, La Palma's fan mussel beds are the place to start rather than spreading your search across the wider Canary archipelago.
Mapping where Fan-shell Associated Shrimp is logged…
Confirmed sightings so far are concentrated at sites in La Palma, Canary Islands, which is currently the only documented region for this species. Divers looking for one should focus searches on fan mussel populations there.
There is no clear seasonal pattern in the data, so sightings are treated as possible year-round. Water temperatures where it has been recorded range from 17.4 to 23.4C, spanning both cooler and warmer months.
Look for a small, pale, semi-transparent shrimp tucked inside the open shell of a fan mussel rather than out on open reef. Its body colour blends closely with the mussel's mantle tissue, so a careful, close look at the shell gap is needed.
Exact size data is not documented for this species, but like most Pontonia shrimps it is small enough to live comfortably within the confined space of a fan mussel's shell.
It spends its entire adult life inside a single fan mussel host, relying on the mussel's filter feeding for scraps rather than hunting on its own. This close, permanent partnership is why divers only ever find it by checking fan mussels directly.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Freshwater Shrimp
2,168 sites
