Magnificent anemone shrimp

A shrimp to about 3 cm with a glass-clear body carrying a white saddle across the middle of the back and a second broad white band over the abdomen, both edged in deep purple to violet. The walking legs are banded purple and white and the antennae are long, white and held well out from the body. It is the most boldly marked of the clear anemone shrimps here, and the dark outlines around the white are the character to go by. Three others cause trouble: the glass anemone shrimp has irregular white patches and a row of round orange spots ringed in black on the tail fan, the graceful anemone shrimp has similar saddles but is spotted red-brown rather than outlined in purple, and the Tosa commensal shrimp is nearly plain with small white spots and no saddle. The separation is a matter of the pattern rather than of anything structural, and a side-on frame of the abdomen is what settles it. The species has been moved out of Periclimenes into Ancylomenes, so guides list it under both names.

The usual hosts are the armed anemones Dofleinia armata and Megalactis griffithsi, which sit half-buried in open sand and silt rather than on reef, and the shrimp is found by finding those anemones and looking along the tentacles. It also turns up on corallimorphs, tube anemones and occasionally on the larger reef anemones. Both of the usual hosts sting strongly enough to raise a welt on a diver’s skin, which is worth knowing before putting a hand down to steady a camera. The shrimp itself is unaffected.

One to three shrimps to a host is normal. It cleans, and small fish will present themselves at an occupied anemone. Recorded from about 5 to 30 m. Being largely transparent it has no outline at all under flat frontal light, and the purple edging is the part of it that reads.