Shrimps - Commensal

The feather star (Crinoid) shrimps in the genus Laomenes are amongst the best know of the commensal Palaemonid shrimps. They closely match the colouration of their host. It is debatable if these shrimps benefit their host, or have a negative effect as they feed on detritus caught in the arms of the feather star.

The almost transparent shrimps that hover over a number of different large sea anenomes are familiar to many. These Periclimenes and Anclyomenes species seem neither to be effected by the stinging cells of the anenome, nor are they attacked by the clown fish that also often live with these anenomes.

Bubble Coral shrimp (Vir) tuck themselves between the polyps only showing their antennae and claws. Popcorn shrimp (Periclimenes kororensis) sit comfortably between the thick tentacles of Mushroon Coral, their white heads looking like the tentacle ends. Eggshell Shrimps (Hemipontonia corallicola) use the same type of camoflage with two large white blotches on their backs.

Other coral shrimps live deep in the branches of corals. The are very shy and difficult to approach. One has even been named the "Furtive Shrimp" (Pliopontonia furtiva) because it is so skittish.

If you look closely at sea-whips, whether they are just 10cm high or several meters long, you often find a number of different animals making their home on them. Pontonoides and Dasycaris are two of the shrimp genera most often seen. They mostly occur as pairs, the male being much smaller than the female. Ther only defence is to quickly go round to the opposite side of the sea-whip if danger approaches.

Hamodactylus shrimps are not found by accident on sea-fans. You must look very carefully to see these almost transparent animals. The colour they have closely matches that of the sea fan, making a sighting doubly difficult.

There area many other commensal shrimps in the Palaemonide. Emperor Shrimps (Zenopontonia imperator) are amongst the most spectacular with their generally scarlet and white patterning. They are often found as pairs on different species of nudibranchs andsea cucumber.

The small shrimp Periclimenes soror is often found in family groups on the undersite of starfish (particularly cusion stars). Their colour invariably matches that of the host.

Ascidians (sea squirts) are another popular host with some species. In the day time these shrimps are deep inside their host, but at night you are sometimes lucky and see them in the "mounth" of the ascidian or foraging on the outside. Periclimenaeus storchi, which looks superficially like a snapping shrimp, is the best known of the ascidian shrimps in Indonesia.

Periclimenes lanipes is actually fairly common, but rarely seen as it lives on the ever-moving branches of basket stars. They are inside the rolled up basket star deep in the reef in the daytime, but start foraging on the branches at night when the basket stars come out to feed. Divers rarely see them as the dive lights cause the basket stars to instantly start escaping back into the reef. Only by using red light can you watch the activities of the shimps and stars without disturbing them.

Thaumastocaris streptopus hides deep in tube sponges, and is cryptically coloured. The best time to see them is at night when the venture to entrance of the sponge to forage on teh surface. Stegopontonia commensalis takes its home up between the protective spinse of long-spined sea urchins,

Urocardella sp. a group of cleaning shrimps that are often seen hovering in groups in the entrance to dark recesses in bommies. The are almost transparent with white antennae which they wave around to attract customers.