Allopontonia brockii

Allopontonia brockii is a small shrimp that lives as a commensal on other animals, belonging to the family Palaemonidae. It is often mistaken for the crinoid squat lobster Allogalathea elegans because both have long claws, a similar cephalothorax shape, a slightly curved abdomen, and matching colors.

However, Allopontonia brockii has a ridged, sharp rostrum with a notch, and its claws are smooth and lack spines. Its body ranges from light yellow to orange-red, with a wide whitish stripe that sometimes has a dark border. Adults reach a maximum length of 1 centimeter (0.4 inches).

This shrimp is found throughout the Indo-Pacific region, including the Red Sea, and along the eastern coast of the Pacific Ocean. It lives as a commensal on several species of sea urchins, such as those in the genera Salmaciella, Salmacis, Asthenosoma, and Pseudoboletiana. It is most commonly seen on the fire sea urchin Asthenosoma varium. The shrimp benefits by riding along as the urchin moves across the seafloor to feed, and it also eats any food particles that get caught on the urchin’s surface.