Astronesthes tchuvasovi

This is a small deep-water fish that carries its own light. Patches of glowing tissue sit on its head and along its sides, and a long feeler hangs from its chin. Divers will not meet it on a normal reef dive. It has been recorded down to 200 m, in salt water.

Other fish in this group look much the same in the water. The chin feeler settles it: check the tip, which is flattened and ribbed with a notch, rather than plain or simply tapered.

Once the fish reaches about 6 cm long, the glowing tissue on its head gathers into a band across the gill cover, the flap over the gills. One or more glowing patches also sit on each flank, near the midline and just ahead of where the pelvic fins start. A barbel, a fleshy feeler, hangs from the chin. It is shorter than the head, and its tip is swollen into a wide, flat lobe with slanted ribs and a small notch in the middle.