Squids and octopuses

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Squids and Octopuses

Cephalopods

Octopus and Squid both belong to the class Cephalopoda, which is part of the phylum Mollusca. The word Cephalopoda is Greek for "head-footed" and refers to the body structure of Cephalopods. There are approximately 800 living species of Cephalopods. The class of Cephalopods contains the two sub-classes Coleoidea and Nautiloidea. Species in the subclass Coleoidea have no shell or an internal shell while those in the Nautiloidea sub class have a shell. Octopus, squid and cuttlefish belong to Coleoidea while the related Nautilus species belongs to Nautiloidea. [1]

Ammonite Fossil

Cephalopods have a fossil record dating back to around 550 million years ago during the Cambrian period. The Nautiloidea are the most primitive of the cephalopods and were quite prevalent during the Paleozoic era during the Ordovican and Silurian periods (about 500 million years ago). Shelled nautiluses at that time were some of the only animals able to swim above the sea floor because of their buoyancy. The Ammonoidea subclass of Cephalopoda is now extinct, but from around 400 to 65 million years ago at the end of the Cretaceous period, these species were important marine animals. Ammonite species had successes and failures resulting in mass extinctions until eventually the entire subclass became extinct. The Coleoidea subclass emerged at around the same time as the Ammonites. Squids and octopuses developed into the modern species they are today, evolving to have less of a shell or no shell at all. The buoyancy that made the Nautilus so successful as a species was no longer as desired for survival and the benefits that came with not having a shell, such as being able to descend deeper into the water, drove the change in the species. Nautiluses today are unable to survive at depths deeper than 500 meters, while many species of squids and octopuses live in far deeper waters. Squid still have internal shells today but these shells are utilized more for structure and rigidity instead of buoyancy. [2]

Squids

Biology

Diagram of the anatomy of a squid

The squid is a cephalopod of the order Teuthida. There are various subcategories, including the genus Heteroteuthis (those that release luminescent ink) and the genus Architeuthis (which contains the Giant Squid). Squids are soft-bodied invertebrates, ranging from 2.5 centimeters to 20 meters long. Typically, they have two tentacles and eight arms. The tentacles are used to catch food, while the arms are for movement. They do have a mouth, hidden between their arms, which vaguely resembles a parrot’s beak. They chew food using their radula, a tongue ringed by teeth. To move around, squids use jet propulsion by expelling water through their mantle cavity. [3]

The most common squid found in reefs, including those at St. John, USVI, is the Caribbean Reef squid. The Caribbean Reef squid (Sepioteuthis sepioidea) is a member of the family Loliginidae. It has a wide and flat body with an average dorsal mantle length of 117mm. [4]

Habitat and Global Presence

Squids are not particularly rare, the common species making a total body mass much greater than that of humans. Rising ocean temperatures, due to climate change, are expected to cause a squid bloom in the coming years since warmer waters help many of them thrive and will expand their living range. [3]
Squids tend to prefer salt water and can be found throughout the oceans of the world, from tropical waters to cooler regions, at various depths, although most live in deep open ocean waters. [5] [3] The largest number of species live in the North Atlantic, although other common locations include the Gulf of Mexico and in the Pacific Ocean near California, Japan, and Hawaii. [6] Larger squids, including the Giant squid and the Colossal squid, often live near the Southern Pole. [6] Caribbean reef squid live all over the Caribbean Sea and off the coast of Florida. They are typically found near shallow reefs, and their exact location depends on their stage in life (see life cycle section).[5]

File:Reef squid.jpg
Picture of a Caribbean Reef Squid


Diet

Squid eat fish, mollusks, and crustaceans, often consuming 30-60% of their body weight on a daily basis. [3] [5] They can also be cannibalistic, eating other squids. [7] Squids catch their prey using suckers on their arms, and they chew using teeth located on their tongue-like muscle in their mouths. [3] The food is chewed up very finely because the particles pass through their esophagus, which has a very narrow track through the brain. [7] Interestingly, Caribbean Reef squid often hunt by imitating other predators, such as parrotfish and typically eat shrimp and smaller fish. Additionally, the Caribbean Reef squid stalks prey, uses luring techniques, and imitates sargassum weed. Most hunting is done at night. . [4]

Predators and Avoiding Predation

Predators of the squid include albatross, sperm whales, sharks, humans, and seals. [5] [3] [8] [7] Yellowfin grouper and similar predatory fishes are specific predators of the Caribbean reef squid. [5] In addition to eating the squid, these predators are known for eating squid eggs. Squid that live in warmer waters tend to have more predators.[8]
Squids can swim more than 23 miles per hour, helping them to evade predation. [3] Squids’ bodies can pale or darken through skin pigment control when retreating or hiding from predators. [5] They accomplish this by purposefully regulating chromatophores with their brain. [4] Additionally, squid can squirt black ink when under stress in order to confuse predators. [3]

Behavior

The Caribbean Reef squid are very social and can be found in groups that help them rest, forage, mate, defend each other, and spawn. These shoals have organized hierarchies, typically based on physical size, but are fluid; squids move between them. Additionally, Caribbean Reef squid have some sort of relationship with certain goatfish, watching over the fish as they hunt. More research is being done on this interaction. [4]

Mating Behaviors

The mating sessions of most squid, typically done in groups, only lasts 15 seconds. [3] Caribbean reef squid, on the other hand, have a longer mating ritual, lasting up to an hour. [5] The male squid penetrates the female mantle with a specialized arm containing spermatophores, and the female lays the eggs in the seabed. [3] The males can fertilize multiple females during the spawning session. [5] Because squid are semelparous (both male and female die soon after reproduction), the females often lay thousands of eggs at the same time. [3]
Here is an example video of the mating ritual between two squids. [9] Female Caribbean Reef squid practice sexual selection and tend to lay seven or eight eggs in a capsule after sexual reproductino. [4]

Life Cycle

Most squid mature to their adult stage in 1-3 years, although this is a different for each kind of squid. [7] Caribbean reef squid grow from 8-9mm mantles to 12-20cm mantles. Juvenile Caribbean Reef squid mature in about six months. [4] When hatched, the baby squid tend to live just below the surface near the shore. Adolescent squid swim a couple meters below the surface and tend to live in shallow turtle grasses. As adults, Caribbean reef squid live in open water in depths up to 100m. [5]

Octopuses

Biology

The octopus is a cephalopod of the order Octopoda. Currently, there are approximately 300 species of Octopus. [1] The majority of octopuses have no internal shell and soft bodies, which allows them to fit into tight places. In this way, octopuses differ from the nautilus, which has an external skeleton and from squids, which have an internal shell. Octopuses have a hard beak, with their mouth at the center of their eight arms, which typically have suction cups. The suction cups have chemoreceptors, which enable the octopus to taste what it is touching. [10] Octopuses have chemicals in their skin that prevent their suction cups from grabbing onto other arms so that their arms do not become tangled. [11]

Close-up picture showing octopus suction cups

An octopus has three hearts: one that pumps blood throughout the body and two that pump blood to each of the two gills. Their blood contains the protein hemocyanin for transporting oxygen, which is less efficient than the hemoglobin found in vertebrates. The hemocyanin is dissolved in the plasma and causes the blood to be blue. [10] Octopuses have brains with folded lobes and visual and tactile memory centers. Octopuses have been shown to store both short and long term memory and are one of the most intelligent invertebrates. A study conducted by the Taiwan National Academy of Science found that the octopus can hear sounds between 400 Hz to 1000 Hz, with its optimum hearing level at 600 Hz. The octopus may use an organ called the statocyst, a sac-like structure containing sensitive hairs, to register sounds. [12] Octopus have sophisticated eyes that contain an iris, slit-shaped rectangular pupil, lens, and a completely "closed" cornea. Below the eyes of the octopus is the hyponome, a muscular tube which when contracted expels water and causes the octopus to be propelled backwards. The hyponome can be aimed in different directions, allowing the octopus to have more control over its movement. [13]

Life Cycle

Octopuses have a short life expectancy, as males typically die soon after mating. Females die after their eggs hatch as a result of starvation from not eating while taking care of their unhatched eggs. For most octopuses, the third arm of the male is modified for transferring packets of sperm to the female. While mating, the male transfers his sperm into the female’s mantle using this modified arm, called a hectocotylus, and then the sperm travels to the female’s reproductive organs. Most female octopuses then lay their eggs on the ocean floor, though some open-ocean species take care of them in their mantle or around their mouth. When octopus hatch the majority look like miniature adults. [10] [14]

Habitat

Octopus are found in many regions of the ocean including coral reefs, open waters, and the ocean floor. Species of octopus common in coral reefs around the Virgin Islands include the Common Octopus, the Caribbean Reef Octopus, and the Caribbean Two-Spot Octopus. Caribbean reef octopuses are common throughout the Western Atlantic, Bahamas, Caribbean, and the northern coasts of South America. They are nocturnal hunters and search for prey among sea grass beds and reefs. Young octopuses grow very quickly and within 17 weeks have reached about 75% of adult size. Males reach sexual maturity in 140 days and females reach maturity in 150 days. [15]

Picture of a Common Octopus


Behavior

Octopuses have many defenses against predators including the expulsion of ink, the use of camouflage and mimicry, quick jet propulsion, and hiding. Ink released by octopuses is thought to reduce their predators’ sense of smell. Octopus also have specialized skin cells that can change the color, opacity, and reflectivity of the epidermis. Changing the color of their skin can be used to communicate with other octopuses and warn them. Some octopuses can also detach and later regrow their arms so that their detached arm serves as a distraction. Octopuses as mentioned above are extremely intelligent and have even been observed using tools. [10][16] When using jet-propulsion, octopuses take in water to the gills and then use their muscles to force the water quickly back out. [1]

Diet

The diet of octopuses depends on their habitat. Bottom dwelling octopuses eat crabs, worms, and other mollusks including whelks and clams. Open-ocean dwelling octopuses eat prawns, fish, and other cephalopods. Octopuses inject prey with a paralyzing saliva before they eat it. [14] When eating mollusks, octopuses first recognize and select their prey and then drill a hole in the shell. Octopus then secrete a substance into the drilled hole, remove the mollusk from its shell, and eat it. Large octopuses have been known to catch and kill some types of sharks.

Relationships with Humans

Octopus face threats from diminishing resources due to the exploitation of the environment. Octopuses are also harmed by the exotic pet trade and animal entertainment industry. Octopuses are difficult to keep in captivity due to their high level of intelligence and ability to problem-solve. While kept in aquariums, they can become weak and prone to sickness because they lack the ability to move around and routinely exercise. [10]

Notes

  1. 1.0 1.1 1.2 "Octopus & Squid Marine Biology." Downbelow: Marine and Wildlife Adventures. Downbelow, 2015. Web. 20 Mar. 2015. <https://www.divedownbelow.com/marine-biology/octopus-and-squid-marine-biology/>.
  2. Monks, Neale. "A Broad Brush History of the Cephalopoda." The Cephalopod Page. Dr. James Wood, 2003. Web. 10 Apr. 2015. <http://www.thecephalopodpage.org/evolution.php>.
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 "A Brief Profile on Squids." Learn About Squids! Tree of Life Web Project, n.d. Web. 25 Feb. 2015. Cite error: Invalid <ref> tag; name "A Brief" defined multiple times with different content Cite error: Invalid <ref> tag; name "A Brief" defined multiple times with different content Cite error: Invalid <ref> tag; name "A Brief" defined multiple times with different content Cite error: Invalid <ref> tag; name "A Brief" defined multiple times with different content Cite error: Invalid <ref> tag; name "A Brief" defined multiple times with different content Cite error: Invalid <ref> tag; name "A Brief" defined multiple times with different content Cite error: Invalid <ref> tag; name "A Brief" defined multiple times with different content Cite error: Invalid <ref> tag; name "A Brief" defined multiple times with different content Cite error: Invalid <ref> tag; name "A Brief" defined multiple times with different content
  4. 4.0 4.1 4.2 4.3 4.4 4.5 McKay, Kelly M. "Caribbean Reef Squid (Sepioteuthis Sepioidea)." Marine Invertebrates of Bermuda. Ed. James B. Wood. BSSR, n.d. Web. 21 Apr. 2015. Cite error: Invalid <ref> tag; name "McKay" defined multiple times with different content Cite error: Invalid <ref> tag; name "McKay" defined multiple times with different content Cite error: Invalid <ref> tag; name "McKay" defined multiple times with different content Cite error: Invalid <ref> tag; name "McKay" defined multiple times with different content Cite error: Invalid <ref> tag; name "McKay" defined multiple times with different content
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 "Reef Squid, Sepioteuthis sepioidea." MarineBio.org. MarineBio Conservation Society. Web. 25 Feb. 2015. Last update: 1/14/2013 2:22:00 PM Cite error: Invalid <ref> tag; name "Reef Squid" defined multiple times with different content Cite error: Invalid <ref> tag; name "Reef Squid" defined multiple times with different content Cite error: Invalid <ref> tag; name "Reef Squid" defined multiple times with different content Cite error: Invalid <ref> tag; name "Reef Squid" defined multiple times with different content Cite error: Invalid <ref> tag; name "Reef Squid" defined multiple times with different content Cite error: Invalid <ref> tag; name "Reef Squid" defined multiple times with different content Cite error: Invalid <ref> tag; name "Reef Squid" defined multiple times with different content
  6. 6.0 6.1 "Squid Habitat." Squid-World. Squid-World.com, n.d. Web. 20 Apr. 2015. Cite error: Invalid <ref> tag; name "Habitat" defined multiple times with different content
  7. 7.0 7.1 7.2 7.3 "Squid." Australian Antarctic Division. Australian Government, 12 Aug. 2010. Web. 15 Apr. 2015. Cite error: Invalid <ref> tag; name "Squid" defined multiple times with different content Cite error: Invalid <ref> tag; name "Squid" defined multiple times with different content Cite error: Invalid <ref> tag; name "Squid" defined multiple times with different content
  8. 8.0 8.1 "Squid Predators." Squid-World. Squid-World.com, n.d. Web. 25 Feb. 2015.
  9. Kahn, Louis. "Rare Squid Mating Caught on Video." YouTube.com. YouTube, 08 July 2012. Web. 21 Apr. 2015.
  10. 10.0 10.1 10.2 10.3 10.4 "Octopus." World Animal Foundation. World Animal Foundation, 2015. Web. 10 Apr. 2015. <http://www.worldanimalfoundation.org/articles/article/8948365/181118.htm>.
  11. Greenfieldboyce, Nell. "Why This Octopus Isn't Stuck-Up." NPR. NPR, 15 May 2014. Web. 8 Apr. 2015. <http://www.npr.org/2014/05/15/312575546/why-this-octopus-isnt-stuck-up>.
  12. Walker, Matt. "The Cephalopods Can Hear You." BBC News. BBC, 15 June 2009. Web. 16 Apr. 2015. <http://news.bbc.co.uk/earth/hi/earth_news/newsid_8095000/8095977.stm>.
  13. Vendetti, Jann. "The Cephalopoda." University of California Museum of Paleontology. UCMP, 2006. Web. 15 Apr. 2015. <http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/cephalopoda.php>.
  14. 14.0 14.1 Wassillief, Maggy, and Steve O'Shea. "Octopus and Squid." Te Ara Encyclopedia of New Zealand. Te Ara Encyclopedia of New Zealand, 12 July 2013. Web. 25 Feb. 2015. Cite error: Invalid <ref> tag; name "Wassillief" defined multiple times with different content
  15. "Caribbean Reef Octopuses, Octopus Briareus." MarineBio. MarineBio Conservation Society, 14 Jan. 2013. Web. 9 Mar. 2015.
  16. http://www.npr.org/sections/thetwo-way/2016/01/28/464447457/shifting-colors-of-an-octopus-may-hint-at-a-rich-nasty-social-life