Discover the beauty and complexity of Photeros annecohenae, a marine bioluminescent ostracod!

     Photeros annecohenae, formerly Vargula annecohenae, is a marine bioluminescent ostracod of the phylum Arthropoda that is found in the Caribbean Sea off the coast of Belize. These ostracods have an outer bivalve carapace composed of chitin that entirely covers the extremities  and functions to protect the organism. They possess many pairs of differing appendages that function in locomotion, sensing the environment, feeding and mating. This organism also contains a light organ that creates chemicals that produce luminescence, a key characteristic of these ostracods.

    Luminescence is of great importance to Photeros annecohenae. Despite the fact that this organism appears mainly translucent in daylight, come nighttime (late twilight), males produce elaborate, species-specific luminescent displays of blue pulses to attract receptive female mates. These mating displays are often more obvious indicators of which species is present than distinguishing a species by morphology. Groups of males will typically synchronize their displays in a process called entrainment, creating captivating light shows of luminescence. Because their courtship displays are similar to those of fireflies, bioluminescent ostracods are often referred to as “marine firefleas” (Morin 1986). Their luminescence is also used to deter predators. When attacked Photeros annecohenae releases a cloud of luminescence that shocks and blinds its predator. The luminescence is also thought to draw secondary predators (the predator’s predator). These are two adaptations that allow the species to thrive in extremely high abundance (over 500 individuals per square meter in some locations) (Gerrish 2009).

     Photeros annecohenae are extremely small, reaching a maximum length of about two millimeters. As mentioned above, their valves contain no pigment, but slight coloration may be seen around the heart, gut, eyes and light organ.    

      This is only a brief summary of Photeros annecohenae. Many do not know about the complexity of this tiny organism. I was one of those individuals, but researching the intriguing organism, especially its use of luminescence during brilliant mating displays and to deter predators, has helped me appreciate not only the complexity of Photeros annecohenae, but the complexity of all organisms on the planet and how they interact. Take a tour of the site, and you’ll see why! Simply click on the links listed to the left or be guided through the website as you read each page by highlighted words within the text or links located at the bottom.

     The photograph at the top of each page was taken at Southwater Key, a location close to Carrie Bow Cay field station where much of the ostracod research used to put this website together has been obtained and studied by Anne Cohen, Elizabeth Torres, Gretchen Gerrish, Jim Morin and Trevor Rivers. It was used with permission from Gretchen Gerrish.

     Since the bioluminescent ostracod is not a part of the group of well-known charismatic megafauna (such as lions, tigers and elephants), you may have never heard of Photeros annecohenae. If this is true, start off your journey of the organism by learning how it is classified as its own species and what organisms it is closely related to!

     As mentioned above, I hope your exploration of Photeros annecohenae leaves you with an even greater appreciation for the complexity of life. To satisfy this new-found appreciation and to learn about other interesting organisms, visit websites created by other UW-La Crosse Organismal Biology students at

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