Caecosagitta macrocephala is a deep sea marine chaetognath that is distributed in meso- and bathypelagic layers.

[3] Along with their eyes, their gut or intestine has orange pigmentation and a luminous organ that gleams due to bioluminescence unlike some other species of Sagittidae.

[4] To be more precise, the luminescent organ is located on the ventral edge of each anterior lateral fin.

[4] It is the only member of the genus Caecosagitta, and only one of the two known species of bioluminescent chaetognath, the other being the distantly related Eukrohnia fowleri.

[2] The luciferase is highly unstable, being unable to survive a single freeze-thaw, and is rapidly inactivated at ice-cold temperatures.