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What is a Cuttlefish? (Sepia Officinalis)
Just from hearing the name, most people would assume that a cuttlefish is indeed a fish. But, in fact, a cuttlefish is actually a species of marine molluscs. Cuttlefish are cousins to oysters and snails and belong to the class Cephalopoda. Cuttlefish live in oceans in most areas of the world. Like a squid, cuttlefish have eight arms and two tentacles. There are around 100 species of cuttlefish around the world. Cuttlefish are well known for their abilities to "color change" and are often called the "chameleons of the sea" due to their ability to blend in with their surroundings. Cuttlefish are one of the most complex invertebrates. They have several million neurons and their brain-to-body mass ratio is more similar to a vertebrate animal. On each side of the brain are two optic lobes that are twice as large as the brain. This shows how important vision is for a cuttlefish to function and most likely is largely due to the cuttlefish needing to analyze their surroundings to blend in.
How Do Cuttlefish Change Color and Shape?
Cuttlefish can change color spectacularly fast and usually the process takes only one second. Cuttlefish have thousands of tiny sacs filled with pigment in their skin. These are controlled by neurons connected directly to their brain. They can produce various designs such as dots or stripes. This color changing is used for warding off predators and for some forms of communication. One unique feature is that the shapes and colors can move across the skin or flash, looking almost like a video projection on the top of their skin. Cuttlefish use various cues such as depth and shadows to sense how to camouflage themselves to their surroundings. Usually, when a predator is near, the cuttlefish will display large black polka-dots across their skin. This tactic is to scare their enemies away. During mating, the cuttlefish can display one pattern towards the same sex and another pattern to attract their mate.
But, they're most likely color blind.
During various studies scientists have noticed between behavioral and psychological traits the cuttlefish is actually color blind. This is quite astonishing considering they can nearly blend into their surroundings and match the colors exactly. To see color, it is required to have two visual photopigments at the very least. Cuttlefish only have one of these, making it impossible to be able to see color. Also, in some situations where a cuttlefish has been laid on a specific pattern, the creature has displayed only one uniform color. What most likely helps a cuttlefish to camouflage blend is their ability of being over sensitive to light. This nearly replaces their need for color vision.
Cuttlefish can slightly change their shape and this is due to not having an actual skeleton. This allows the cuttlefish to morph into different shapes. This can make them less appealing for a predator and can even make them appear threatening. This shape shifting can be seen in the video below where you can see the cuttlefish create "spikes" on their skin.
The Unique Anatomy
The anatomy of the cuttlefish is unique in many ways. The two long tentacles on the front of the cuttlefish are used for mating and catching prey. The tentacles retract when not in use and can shoot out when needed. One unique parts of a cuttlefish is called the mantle. The mantle functions by bringing in water and then pushing it out at high rates of speeds to help the cuttlefish escape a predator. Cuttlefish are buoyant by a structure called the cuttlebone. The cuttlebone is similar to a fish's swim-bladder. It is a porous structure that regulates the ratio of liquid and gas via the ventral siphuncle.
This allows the cuttlefish to float upwards or rest at the ocean floor at it's convenience.
Cuttlefish have three hearts instead of one. Two of the hearts have the job of pumping blood to each of the gills, the remaining heart pumps blood to the rest of the body. Interestingly enough, a cuttlefish's blood is not red. The blood of a cuttlefish is a blue-green color due to containing copper instead of iron.
Figure 1. Cuttlefish life history and behavior. (Left)
(A) Adult cuttlefish mating in a typical head-to-head position (male on right; from www.divephotoguide.com). (B) Cluster of eggs stained in black by the female ink (Sepia officinalis) laid on a rope (English Channel, off Ouistreham, France. Image with permission from Olivier Basuyaux). (C) Cuttlebone washed-up on the beach in Normandy (France) after the season of reproduction and the death of the adults. (D) Late-staged embryo seen through the egg capsule after removal of its outer layers, in a ventral position just before hatching. (E) Juvenile cuttlefish displaying a disruptive body pattern on a variegated substrate made of pebbles of different sizes and colours. (F) Cross-section of the brain of a 30-day-old cuttlefish stained in blue. The arrow indicates the esophagus, which splits the central mass into a supra-esophageal mass (M) and a sub-esophageal mass (m). The optic lobes are situated laterally (OL); LE, left eye; RE, right eye (image with permission from Christelle Jozet-Alves). Scale bar = 0.08 cm.
(Figure provided by Current Biology)
Diet
In a study off the coast of Portugal, 522 cuttlefish were caught and their stomach contents were identified. The total number of prey inside the digestive system was 49 specimens of six different taxa. Their feeding patterns were concluded to be opportunistic. The study looked at the season, the sex, and the size of the cuttlefish. It was found that male and female cuttlefish had similar diets. The most significant data concluded that size was the main determining factor of what a cuttlefish chose to prey on. There seemed to be a change in diet between the seasons, but this was likely due to the size of the cuttlefish in that season. In small cuttlefish, crustaceans were often the choice of food. But, fish were often eaten by larger cuttlefish. Cuttlefish do have a stomach and a digestive gland. Waste is excreted out of the anus.
Reproduction and Life Cycle
Males attract female cuttlefish with their vibrant colors. Males are very aggressive towards other males due to the ratio of males to females usually being 2:1. Females tend to be picky and will not go for the largest organism, she will often go for the male cuttlefish with the smartest strategies. The cuttlefish are gonochoristic and they produce sexually by external fertilization. As shown in figure 1 box A, the cuttlefish will mate head to head. The female stores fertilized eggs in a pouch by her mouth. Cuttlefish reproduce in springtime and the females lay hundreds of eggs in only a couple days. Females die within days of laying her eggs. Cuttlefish offspring hatch a miniature adults and reach adulthood at around 18-22 months. The average lifespan of a cuttefish is around 2 years old.
Fun Facts!
-Male cuttlefish will disguise themselves as female cuttlefish to sneak past other male cuttlefish during mating season!
-They can count! In a study, 1 month old cuttlefish could distinguish between a box of 4 shrimp VS. a box of 5 shrimp.
-They're watching you! Cuttlefish can actually see behind them because they have W-Shaped pupils.
Bibliography
1) Alves, Dário Mendes, et al. “Diet of the Cuttlefish Sepia Officinalis (Cephalopoda: Sepiidae) off the South Coast of Portugal (Eastern Algarve).” Journal of the Marine Biological Association of the United Kingdom, vol. 86, no. 2, 2006, pp. 429–436., doi:10.1017/S0025315406013312.
2) Lopes, Vanessa, et al. “Cephalopod Biology and Care, a COST FA1301 (Cephs In Action) Training School: Anaesthesia and Scientific Procedures.” Invertebrate Neuroscience, vol. 17, no. 3, 2017, pp. 1–8.
3) Darmaillacq, Anne-Sophie, and Daniel Osorio. “Cuttlefish.” Current Biology, vol. 27, no. 20, 23 Oct. 2017, pp. R1093–R1095.
4) Chiao, Chuan-Chin, and Roger T. Hanlon. “Cuttlefish Camouflage: Visual Perception of Size, Contrast and Number of White Squares on Artificial Checkerboard Substrata Initiates Disruptive Coloration.” Journal of Experimental Biology, The Company of Biologists Ltd, 15 June 2001, jeb.biologists.org/content/204/12/2119.short.
5) Arkley K, Jacklin MS, Boulter M, Tower J. 1996. The cuttlefish (Sepia officinalis): a guide to its exploitation in UK waters. The Seafish Industry Authority. Report number SR467
6) Cephalopod [Internet]. c2013. Encyclopedia Britannica
7) Pechenik JA. 2010. Biology of the Invertebrates. 6th ed. New York, NY. The McGraw Hill Companies; 256-293p
(Cites 5, 6, 7, found https://cuttlefishsepiida.weebly.com/reproduction-and-life-cycle.html)
Photo and Video Sources
http://extrememarine.org.uk/2016/11/curious-case-of-the-giant-cuttlefish/
http://www.sciencedirect.com.proxy.lib.iastate.edu/science/article/pii/S0960982217311107
http://mentalfloss.com/article/66759/10-colorful-facts-about-cuttlefish
https://www.youtube.com/watch?v=Fw7rebr5aJA
http://www.telegraph.co.uk/news/picturegalleries/picturesoftheday/10161725/Pictures-of-the-day-5-July-2013.html?frame=2608650
http://bioweb.uwlax.edu/bio203/f2013/ziegler_kyle/adaptation.htm
Fun Facts
http://mentalfloss.com/article/66759/10-colorful-facts-about-cuttlefish
https://www.mnn.com/earth-matters/animals/blogs/5-amazing-facts-about-strange-beautiful-cuttlefish
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