Researchers have discovered a curious new bioluminescent creature attached to the shells of sea snails in the Red Sea. Describing the finding in the journal PLOS ONE, the study authors are unable to explain the nature of the apparent symbiotic, or mutually beneficial, relationship between the two animals, as this represents the first example of fluorescent hydroids attaching themselves to another organism in this way.
Further analyzing the nature of this intriguing new specimen, the study authors note that the pattern of fluorescence exhibited by the creature appears to be species-specific. As such, they suggest that fluorescence may provide a useful way of identifying species that are otherwise almost impossible to recognize.
Hydroids are very small aquatic predators that are related to jellyfish and coral, and pass through various life stages. The green-glowing specimens described in the study were all in the asexual polyp stage, and were found living in colonies at depths of between 3 and 8 meters (10 and 26 feet).
Green fluorescence, such as that exhibited by the species under discussion, is generated by proteins called green fluorescent proteins (GFP), which glow when they are illuminated by moonlight or sunlight. In this way, they allow certain animals to light up at night. Interestingly, there have been very few documented examples of green fluorescence in hydroids.
The hydroids were found on the shells of a type of snail called Nassarius margaritifer, which spends its days buried in the seabed before emerging to hunt at night. As such, the researchers suggest that the presence of these tiny fluorescent creatures on their shells may somehow aid them in their nocturnal search for food, perhaps by attracting prey – although this has not yet been confirmed.
Taking a closer look at the morphology of the hydroid, the researchers were able to identify it as a member of the Cytaeis genus, since it displayed many of the physical traits common to this group of animals. For instance, the size of the polyps and the number of tentacles were all consistent with those of other Cytaeis species.
However, the arrangement of GFPs across the polyps was unlike that of any previously recorded species, leading the investigators to conclude that they were indeed looking at a brand new species. Based on this observation, they claim that studying the distribution and intensity of fluorescent points on the bodies of bioluminescent animals can provide a useful method for the “identification of cryptic species.”