Stalking the wily night critters: Hinge-beak shrimps

by B. N. Sullivan

Imagine that it's just after dark.  You jump off the stern of the boat into the water and descend to the reef.  You switch on your light and sweep the beam  left and right to get your bearings.  You see little blinking red lights all over the place. What the...??

Don't be alarmed.  Aliens have not landed and dispersed on the reef.  What you probably are seeing are reflections from the eyes of tiny critters called Hinge-Beak Shrimps.  All of the shrimps in this family have big googley eyes that reflect when a beam of artificial light is shone on them.

These creatures of the night are little guys, usually between 3 cm to 5 cm (1.25 in to 2 in) in length. They hide all day -- who knows where?  At night they come out to feed,  often in large numbers, but they're not easy to find then either.  Oh, you definitely will see those blinking red lights I mentioned, but if you try to find the actual critter behind the pinpoint of red light you will be unsuccessful much of the time.  These critters are extremely shy, so as soon as you get near -- piff! -- they're gone!

I had wanted to photograph one of these critters for years before I finally managed to do so.  I succeeded in capturing the macro image you see on this page by concentrating very, very hard on where one of those red dots of light seemed to be, then switching off my light and sneaking up to the presumed spot.  In this instance, the tiny red light  seemed to be coming from a pencil urchin, so I assumed the shrimp was hiding among the urchin's thick spines.  I  knelt down very close to the urchin while Jerry shone a small light beam near to it, but not on it, giving me just barely enough light to set up the shot.  I pressed the shutter release and  voilà! Gotcha!

Now, about that funny name, Hinge-beak shrimp.  Shrimps in this family (Rhynchocinetidae) have a beak-like rostrum that can bend.  In fact, the name Rhynchocinetidae actually means 'movable beaks'.  Other kinds of shrimps do not have this feature.

We first encountered these shrimps in the Caribbean Sea where the dive guides called them Red Night Shrimps.  It turns out that the shrimps' bodies are mostly red, but that name referred to the red glow from their eyes at night.  We have since seen species from this family almost everywhere we have dived around tropical reefs at night: Caribbean, Red Sea, Hawaii, and throughout the Indo-Pacific region.  Each locale seems to have its own common name for the creatures in this family.  We think the name Red Night Shrimps really suits them, so that is what we like to call them.