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Brief Summary

    Brief Summary
    provided by EOL authors

    The bobtail squid, (Euprymna scolopes) is a small cephalopod that lives in the shallow water off the coast of several of the Hawaiian Islands.The bobtail squid averages 3 cm in length when fully grown (McFall-Ngai, 2008) and its skin is patterned with stripes, blushes, and spots.The squid’s general tone color varies from light tan to dark chocolate and its skin produces a sticky adhesive (Moynihan, 1983).This small carnivore eats tiny fish, shrimp and worms in the water at night, but buries itself in the sand during the day (Moynihan, 1983, Gillis, 1993).The bobtail squid has formed a symbiotic relationship with Vibrio fischeri, a bioluminescent bacterium which colonizes a special light organ in the squid’s mantle (McFall-Ngai, 2008).This small creature uses the light produced by V. fischeri to camouflage from its prey and from predators such as eels, lizard fish (Gillis, 1993) or crabs swimming in the water column (Anderson and Mather, 1996).At dawn, the squid expels 95% of the bacteria from its light organ into the surrounding environment, providing newly hatched juveniles with symbionts and preventing the colony in the host from overpopulating.

    Euprymna scolopes: Brief Summary
    provided by wikipedia


    Euprymna scolopes, also known as the Hawaiian bobtail squid, is a species of bobtail squid in the family Sepiolidae native to the central Pacific Ocean, where it occurs in shallow coastal waters off the Hawaiian Islands and Midway Island. The type specimen was collected off the Hawaiian Islands and is deposited at the National Museum of Natural History in Washington, D.C..

    Euprymna scolopes grows to 30 mm (1.2 in) in mantle length. Hatchlings weigh 0.005 g (0.00018 oz) and mature in 80 days. Adults weigh up to 2.67 g (0.094 oz).

    In the wild, E. scolopes feeds on species of shrimp, including Halocaridina rubra, Palaemon debilis, and Palaemon pacificus. In the laboratory, E. scolopes has been reared on a varied diet of animals, including mysids (Anisomysis sp.), brine shrimp (Artemia salina), mosquitofish (Gambusia affinis), prawns (Leander debilis), and octopuses (Octopus cyanea).

    The Hawaiian monk seal (Monachus schauinslandi) preys on E. scolopes in northwestern Hawaiian waters.

Comprehensive Description

Distribution

    Distribution
    provided by Animal Diversity Web

    Euprymna scolopes is a sepiolid squid endemic to the oceanic habitats surrounding the Hawaiian Islands. This squid can greatly affect the relative abundance and geographic distribution of its bacterial symbiont Vibrio fischeri.

    Biogeographic Regions: pacific ocean (Native )

Morphology

    Morphology
    provided by Animal Diversity Web

    Euprymna scolopes is one of the smallest and slimmest sepiolid squids. The mantle plus tentacles measure an average of 35 mm (1.4 in) in length, and weighs an average of 2.76 grams (0.09 oz). The birth mass of a hatchling is an average 0.005 grams (0.00018 oz). Males have slightly larger suckers than females, with thinner posterior mantles. Both sexes have a pair of unique paddle shaped fins that aid in swimming. A feature unique to Euprymna scolopes is the bilobed and bioluminescent light organ present inside the squid’s mantle cavity. This organ, which functions through its interaction with its symbiotic partner Vibrio fischeri, provides light, allowing the squid to hunt its prey at night. This squid also possesses metabracial vesicles, which function as the eyes of this bobtail squid. The vesicles allow the squid to perceive and manipulate the amount of light it can give off, so the squid can camouflage itself in a process known as counterillumination.

    Range length: 20 to 30 mm.

    Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

    Sexual Dimorphism: sexes shaped differently

Habitat

    Habitat
    provided by World Register of Marine Species
    Shallow coastal waters.
    Habitat
    provided by Animal Diversity Web

    Euprymna scolopes is found in warm, shallow coastal waters 2-4 cm deep. This is unusual because most sepiolid squids reside in very deep water. Euprymna scolopes is often seen laying its eggs on the foundations of coral ridges. During the day, these squid are buried in the sand. At night, they emerge and wade through the sand with their bioluminescent light organ which allows them to see and hunt in the dark.

    Habitat Regions: tropical ; saltwater or marine

    Aquatic Biomes: benthic ; coastal

Trophic Strategy

    Trophic Strategy
    provided by Animal Diversity Web

    The primary component of the adult E. scolopes diet is mysid shrimp, and younger squids will also consume crustaceans in the genus Artemia. Euprymna scolopes is a cryptic "sit and wait" predator. The squid buries itself in the sand with its tentacles and wait for prey to pass by. Euprymna scolopes attacks by aiming all the arms at the prey and strikes using the two tentacles. If the squid misses the prey it remains buried and waits for another organism.

    Animal Foods: aquatic crustaceans

    Primary Diet: carnivore (Eats non-insect arthropods)

Associations

    Associations
    provided by EOL authors

    E. scolopes, similar to other luminous cephalopods emits a polarized light pattern on its surface.This light emitting capability comes from a bacterial population of Vibrio fischeri .Vibrio fischeri is a bioluminescent bacterium which colonizes a special light organ in the squid’s mantle (McFall-Ngai, 2008) which is stored in a special light organ inside the squid’s mantle (Shashar and Hanlon, 1997).The bioluminescent bacterium V. fischeri has developed a mutualistic symbiotic relationship with E. scolopes in which V. fischeri gives the bobtail squid bioluminescence in trade for nutrients (Gillis, 1993).The bobtail squid can survive without its symbiont, and cultures of V. Fischeri are easily grown, making this an excellent model system for studying animal-bacteria symbiotic relationships (McFall-Ngai, 2008).

    The bobtail squid’s luminescence is the product of a chemical reaction between V. fischeri and E. scolopes, a defense mechanism by V. fischeri activated to prevent the host from producing too much hydrogen peroxide (Ruby and McFall-Ngai, 1999, Archetti et al., 2011).Hydrogen peroxide, as well as other reactive oxygen species (ROS) such as hypochlorous acid bind otherwise available oxygen and in consequence, reduce growth in the bacterial population (Ruby and McFall-Ngai, 1999).E. scolopes does not retain this bioluminescence while buried during the day; rather it uses it at night for hunting (Shashar and Hanlon, 1997).The bobtail squid turns off its bioluminescence by ejecting 90-95% of its bacterial symbiont at dawn, (Visick and Ruby, 2008) and takes on the shades and colorings of the surrounding sand.The bacteria repopulate inside the squid during the day.At night when E. scolopes becomes predatory, it activates its lustrous colors by feeding its bacterial symbiont oxygen. (Boettcher et al. 1996).

    Associations
    provided by Animal Diversity Web

    Euprymna scolopes has a mutualistic relationship with the marine bacteria Vibrio fischeri, making the squid bioluminescent.

    Although they are inhabitants of areas near coral reefs, there is no evidence to suggest Euprymna scolopes has an effect or relationship on the maintenance of the community around the reef.

    Mutualist Species:

    • Vibrio fischeri
    Associations
    provided by Animal Diversity Web

    As previously mentioned, Euprymna scolopes uses counterillumination to camouflage from predators. Another defense mechanism is burying itself in an outer covering made of sand. Last, the squid releases an amount of ink when they sense a stimuli indicating the presence of a predator. The pool of ink is used to deceive the predator and prevent attack by resembling the shape of the squid. Known predators of E. scolopes include lizardfish (family Synodontidae), barracuda (genus Sphyraena), and Hawaiian monk seal (Monachus schauinslandi).

    Known Predators:

    • lizardfish, Synodontidae
    • barracuda, Sphyraena
    • Hawaiian monk seal, Monachus schauinslandi

    Anti-predator Adaptations: cryptic

Behavior

    Behavior
    provided by EOL authors

    E. Scolopes is a solitary animal unlike its relative the cuttlefish, which interacts with others within a social group.Both male and female E. Scolopes are predators that are active nocturnally.They only interact when mating (Shashar and Hanlon, 1997), and typically avoid other individuals in captivity and in the wild. (Moynihan, 1983). E. Scolopes typically rests beneath a layer of sand during the day. By moving its tentacles in a synchronous sweeping motion, it moves sand over its body until completely buried.This behavior is a simple technique to avoid being preyed upon. This tiny squid also secretes an adhesive from its skin which aids in keeping sand on its body. (Moynihan, 1983)

    The carnivorous bobtail squid enters the water column and preys primarily on shrimp and worms at night.Rather than using bioluminescence as a communication tool, the bobtail squid uses this adaptation to avoid casting a shadow. Counterillumination, specifically, allows E. scolopes to imitate the light shed by the moon and stars, become camouflaged, and remain unnoticed by prey or predators (McFall-Ngai, 2008).It sits and waits on the sandy floor for prey to come near and suddenly points all of its tentacles at its target.In a moment, it jets toward its prey and snatches it with its two main arms (Fleisher and Case, 1995).Unlike most other carnivores, the bobtail squid first begins eating its prey from the tail end. (Moynihan, 1983).

    The bobtail squid may ink and use jet propulsion as an escape mechanism to confuse predators of its location.They can quickly travel 1 m in this way by jetting, while also changing the patterns on their bodies. (Anderson and Mather, 1996).

    Behavior
    provided by Animal Diversity Web

    Euprymna scolopes has a symbiotic relationship with a bioluminescent marine bacterium called Vibrio fischeri. This mutualistic relationship begins early in the life stages of the squid and development of the light organ results. The squid controls the amount and timing of the bioluminescence given off by the bacteria. When the bacteria are found outside of this mutualistic relationship the strength of the light given off is not nearly as strong as it is when it is housed inside the light organ of E. scolopes. This light organ is generally used for a specialized behavior known as counterillumination, which allows the organism to camouflage themselves and avoid predators.

    Communication Channels: tactile ; chemical

    Other Communication Modes: photic/bioluminescent

    Perception Channels: polarized light ; tactile ; chemical

Life Cycle

    Life Cycle
    provided by Animal Diversity Web

    Euprymna scolopes develops rapidly and grows exponentially. After copulation, there is a 18-26 day embryonic period. The planktonic hatchling first emerges from the egg, and is initially aposymbiotic, meaning it cannot use its light organ. After several days, the hatchling develops into a planktonic paralarva that can partially make use of the light organ. The paralarva develops into a juvenile after ten days, and becomes mature enough to travel into shallower waters. After 130 days, when the squid is a subadult, the light organ fully functions for hunting and camouflage. The squid will have little to no further growth after 180 days. Male and female organisms, which occur in equal numbers, reach sexual maturation 60 days after hatching. Temperature may be a factor in the time to reach full sexual maturity. Interaction with Vibrio fischeri is not required for normal development and growth.

    Development - Life Cycle: metamorphosis

Life Expectancy

    Life Expectancy
    provided by Animal Diversity Web

    Euprymna scolopes has a lifespan that averages 2-3 months in the wild and 3-5 months in captivity.

    Typical lifespan
    Status: wild:
    2 to 3 months.

    Typical lifespan
    Status: captivity:
    3 to 5 months.

Reproduction

    Reproduction
    provided by EOL authors

    Mating in E. scolopes has been studied in laboratory settings.A male will gradually flatten itself on top of a female.It will then shift its position upward and move its arms underneath the female and the two will coil their arms together as a mass of sperm is transferred from the male to the female. (Moynihan, 1983).Females can lay 50-200 eggs per clutch.Unlike most species of cephalopod, females do not die after reproduction and can lay numerous clutches every few days (Montgomery and McFall-Ngai, 1993).Embryos will develop for approximately 20-23 days depending on environmental temperatures (Montgomery and McFall-Ngai, 1993), before hatching.

    During the first hour after hatching, there is a permissive period in which many different kinds of bacteria enter a crypt in the tissue of the light organ from the surrounding seawater.However, at approximately the 1- 2 hour mark, a restrictive period occurs in which no bacteria can enter the organ.After this period, only V. fischeri are allowed to enter the squid’s light organ, and depending on the concentration of V. fischeri cells in the surrounding seawater, full colonization of the host can take between 8 and 48 hours (Nyholm and McFall-Ngai, 2004).

    At dawn each day, adult bobtail squid expel 95% of the bacteria living in its light organ into the surrounding seawater (Visick and Ruby, 2008).Since juveniles stay within the vicinity of the parent population and do not disperse into the larger ecosystem, this daily expulsion and enrichment of V. fischeri from adults into the local environment is crucial for establishing the symbiosis wherein juveniles are colonized during their first minutes and hours of life (Nyholm and McFall-Ngai, 2004).

    Reproduction
    provided by Animal Diversity Web

    There is no information on the mating system of Euprymna scolopes.

    Mating is initiated by the male, which grabs the female and places its spermatophore in the female's mantle. The female's mantle will become larger as it is filled with eggs. Mating lasts 30-50 minutes, and occurs mostly at night. Studies have shown that rainfall increases the amount of breeding. There are no specific seasonal breeding intervals for this squid. Females tend to lay eggs in the morning in shallow areas on coral ridges. Clutch sizes vary between 50-200 eggs. It takes an average 30 minutes to lay each clutch of eggs. The number of clutches each female lays varies greatly. After females are finished laying eggs, they cover them with sand and then depart, leaving the offspring to fend for themselves.

    Average number of offspring 100-150

    Range number of offspring: 50 to 250.

    Average number of offspring: 100-150.

    Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous ; sperm-storing

    The female lays clutches of eggs and covers the eggs with sand after which there are no interactions.

    Parental Investment: pre-hatching/birth (Protecting: Female)

Conservation Status

    Populations and Conservation
    provided by EOL authors

    The bobtail squid lives in abundant populations off the coast of Hawaii (McFall-Ngai, 1994), and while no exact population count exists for the species in the wild it has been estimated that there are close to 45,000 individuals living in Kaneohe Bay (McFall-Ngai, unpublished, 2017).It was found that 8-10 sexually mature pairs of adults could produce approximately 60,000 juveniles in one year when in captivity (McFall-Ngai, 2014).The main predators of the bobtail squid are fish, eels (Gillis, 1993), and crabs, though escape behavior such as jetting and inking may give the squid an advantage at avoiding being preyed upon (Anderson and Mather, 1996).There is currently not enough information on E. scolopes to determine if the population is threatened on a global scale (Barratt, I. & Allcock, L. 2012).

    Conservation Status
    provided by Animal Diversity Web

    Euprymna scolopes is classified by IUCN as Data Deficient because of the uncertain status of its taxonomy (genus and species).

    US Federal List: no special status

    CITES: no special status

    State of Michigan List: no special status

Benefits

    Benefits
    provided by Animal Diversity Web

    There are no known negative effects of Euprymna scolopes on humans.

    Benefits
    provided by Animal Diversity Web

    There is no information indicating any positive effects by Euprymna scolopes on humans.