Caecosagitta
Caecosagitta macrocephala is a deep sea marine chaetognath that is distributed in meso- and bathypelagic layers. It has a very wide distribution that ranges from the Subantarctic to Subarctic Ocean. [3] Cecosagitta macrocephalas have large heads, hence their name “macro-cephala”. Within their eyes are photoreceptive regions that allow them to catch weak light at bathypelagic depths.[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.[1] C. macrocephala has a secreted bioluminescence that is thought to be coelenterazine based.[1] The luciferase is highly unstable, being unable to survive a single freeze-thaw, and is rapidly inactivated at ice-cold temperatures.
| Caecosagitta | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chaetognatha |
| Class: | Sagittoidea |
| Order: | Aphragmophora |
| Family: | Sagittidae |
| Genus: | Caecosagitta Tokioka, 1965[1] |
| Species: | C. macrocephala |
| Binomial name | |
| Caecosagitta macrocephala (Fowler, 1904)[2] | |
Caecosagitta macrocephala's bioluminescent organs consist of hexagonal chambers containing elongate ovoid particles—the organelles holding bioluminescent materials. No other luminous organism is known to use hexagonal packing to hold bioluminescent materials. [4]
Caecosagitta macrocephala found in the north-western Pacific and centre-east to south Atlantic Oceans, were found to consists of at least two cryptic species due to "speciation of the bathypelagic species from a mesopelagic precursor."[3]
References
- Tokioka, T. (1965). The taxonomical outline of Chaetognatha. Publications of the Seto Marine Biological Laboratory, 12(5), 335–357.
- Fowler, G. H. (1905). Biscayan plankton. Part III.—The Chætognatha. Transactions of the Linnean Society of London, (2)10, 55–87.
- Miyamoto, H., Machida, R. & Nishida, S. (2010). Genetic diversity and cryptic speciation of the deep-sea chaetognath Caecosagitta macrocephala (Fowler, 1904). Deep-Sea Research Part II: Topical Studies in Oceanography, 57(24–26), 2211--2219.
- Thuesen, E. V., Goetz, F. E. & Haddock, S. H. (2010). Bioluminescent organs of two deep-sea arrow-worms, Eukrohnia fowleri and Caecosagitta macrocephala, with further observations on bioluminescence in chaetognaths. Biological Bulletin, 219(2), 100–111.