Last week, we highlighted a tarantula that uses structural characteristics to produce a vibrant blue color so this week, I thought I would continue with the structural color theme, but this time by featuring a marine invertebrate. Meet the sea sapphires, of the genus: Sapphirina.
Sea sapphires are enigmatic parasitic copepods which can be found in oceans all over the world. Female sea sapphires are transparent and parasitize tubular, gelatinous animals known as salps in order to reproduce.
Salps are a strange group of planktonic tunicates which cruise around the sea feeding on phytoplankton and are often found in interlinked aggregate chains which are formed during asexual generations.
Male sea sapphires on the other hand, while also transparent, have the ability to shimmer when exposed to light. They possess multilayered platelets in the epidermal cells of their dorsal and ventral integument which basically means that male sea sapphires have a sort of crystal skin containing parallel layers of honeycombed prisms.
When light contacts these layers, it can reflect and produce iridescence. Also, depending on the size of the space between these layers, the structural color effect may favor a particular color such as blue or gold.
The exact purpose of this ability appears to be unknown but I would venture that it has something to do with reproduction given the sexual dimorphism (i.e. only males produce color) and the fact that the females have huge eyes compared to the males (implying that they may be extra sensitive to flashiness)
Regardless of the exact purpose, sea sapphires are intriguing and beautiful little invertebrates. If you’d like more information on sea sapphires, I recommend starting with this article by Deep Sea News which features video of shimmering sea sapphires.
References and Further Reading
- A. C. Heron (1973). A Specialized Predator-Prey Relationship Between the Copepod Sapphirina Angusta and the Pelagic Tunicate Thalia Democratica. Journal of the Marine Biological Association of the United Kingdom, 53, pp 429-435. doi:10.1017/S0025315400022372.
- Jinho Chae and Shuhei Nishida (2004). Swimming behaviour and photoresponses of the iridescent copepods, Sapphirina gastrica and Sapphirina opalina (Copepoda: Poecilostomatoida). Journal of the Marine Biological Association of the UK, 84, pp 727-731. doi:10.1017/S0025315404009816h.
- Jinho Chae and Shuhei Nishida (1999). Spectral patterns of the iridescence in the males of Sapphirina (Copepoda: Poecilostomatoida). Journal of the Marine Biological Association of the UK, 79, pp 437-443.
- Jinho Chae and Shuhei Nishida (1994). Integumental ultrastructure and color patterns in the iridescent copepods of the family Sapphirinidae. Marine Biology, May 1994, Volume 119, Issue 2, pp 205-210
- Elofsson R (1969) The ultrastructure of the nauplius eye of Sapphirina (Crustacea: Copepoda). Z Zellforsch 100: 376–401