Vampyroteuthis infernalis

"Vampire Squid"

Kristine Murphy, Fall 2022

Kingdom: Animalia

Phylum: Mollusca

Class: Cephalopoda

Family: Vampyroteuthidae

Genus: Vampyroteuthis

Species: Vampyroteuthis infernalis

Morphology

Like many deep-sea dwelling creatures, V. infernalis have a cryptic body color ranging from deep red to black, allowing them to blend in with their dimly lit surroundings. Their bodies grow to about a foot long, and are semi-gelatinous with two fins on their mantle, used as their primary locomotory source. They have massive eyes which appear blue in photographs from the lights casted by the Remotely Operated Vehicles (ROVs) observing them. According to MBARI, they have the biggest eyes of any living animal proportional to body size!

They have different type of light organs on their body (see "Bioluminescent Display").

Pairs of cirri-harmless spikes- line the entire length of the 8 arms' underside, while suckers are only located on the distal end (uncommon for octopods and squids). A large web encases the arms, along with two retractile filaments which are kept in pouches between the first and second arms. The filaments are believed to be analogous to the feeding tentacles of squids, which they also share the feature of a gladius with.

Juvenile V. infernalis have 2 pairs of fins, but one pair shrinks and eventually disappear, while the remaining pair shift up the mantle as the individual matures into adulthood.

Cirri (spikes) as well as red suckers on distal ends of arms

Juvenile with two pairs of fins

Life in the Oxygen Minimum Zone

V. infernalis are distributed globally in the Meso- to Bathypelagic zones of tropic and temperate regions, reaching depths of 600-1200 meters. Specifically, they live in the Oxygen Minimum Zone, an area containing only 5% oxygen saturation. The highly successful and specific adaptations of V. infernalis have allowed them to inhabit this environment, and is an incredible feat, considering most cephalopods cannot tolerate environments with an oxygen saturation lower than 50%.

Adaptations to the Oxygen Minimum Zone's hypoxic environment:

Minimal use of active locomotion:
- The pair of fins undulate and allow the individual to leisure around
- Jet propulsion can be briefly used when needed
- Very low amounts of muscle mass
Natural buoyancy allows minimal energy expenditure needed to stay afloat
- - Unique and highly developed statocyst help maintain orientation
    - Statolith has characteristics of both octopods and squid, and some of neither
  - Large amount of ammonium in tissues, which has slightly higher density than water
Extremely low metabolism
- Allows for low amount of oxygen intake
- Lowest mass-specific metabolic rate in cephalopods
Large oxygen affinity in blood:
- Hemocyanin has a higher affinity for oxygen than hemoglobin
- V. infernalis have the second highest oxygen affinity in all cephalopods which use hemocyanin
Detritivore feeding habit
- Do not actively hunt food, instead are relatively opportunistic (see "An Unappetizing Diet")
Large eyes
- Very sensitive to dim light
- Probably can see larger food particles/aggregates

Retractile filament deployed

Scraping retractile filament onto suckers

The small white speckles are pieces of marine snow

An Unappetizing Diet

The name "vampire squid" insinuates a blood-drinking diet, such as the similarly named "vampire bat". Unlike other coleoid cephalopods, which are almost exclusively carnivorous predators, V. infernalis are detritivores.

Detritivores feed on dead organic matter. They are important in nutrient cycling, as they prevent the buildup of dead, rotting material. V. infernalis are the only living cephalopods which do not eat live prey, according to the MBARI.

Studies³ examining the contents of the digestive tract, regurgitations, droppings, and observation of food being eaten in situ have found V. infernalis consume marine snow- organic material trickling down from the shallower parts of the ocean. Specific examples of marine snow found to be ingested by V. infernalis are: crustacean setae molts, antennae, and eyes, as well as larvacean fecal pellets, marine aggregates, gelatinous tissue, diatoms, eggs, and copepods.

Feeding Mechanism: catching snowflakes

How do V. infernalis acquire marine snow? Their retractile filament emerges, usually one at a time, from a pocket between the first and second pair of arms, and extends away from the body, up to 8x the body length. These filaments are analogous to the feeding tentacles of squids, except they cannot grab food via suction. Instead, small, sticky hairs on the filament collect the marine snow, then retract inwards towards the distal portion of the arms, which contain the suckers. These suckers secrete mucus, mixing with the food as the filaments drag them across, creating a ball of mucus and food, called bolus. The cirri then transport bolus along the arm webs to the mouth, where it is ingested.

This food source clearly does not provide a large amount of calories or energy- this is no problem, since their extremely low metabolism and energy expenditure on locomotion and feeding mechanism allow for a more leisurely, low-energy lifestyle.

Further findings of retractile filaments

The retractile filaments are used for feeding, but there's more information under the skin. The layer of sensory cells sit on top a large nerve, which connects to the ventral magnocellular lobe of the brain. The function of this lobe in V. infernalis is currently unknown, but large amounts of signals are being sent to it by the sensory cells. It's believed the sensory cells are informing the brain of the presence of food.

³Cross Section of sucker, showing goblet cells (pink) which secrete mucus

Trophic Ecology

Nitrogen studies of hard parts and beaks of cephalopods tell which trophic level they occupy. A lower trophic level indicates being lower on the food chain, while a higher level being a predator. Normally, cephalopods occupy a high level since they are carnivorous predators, and they tend to climb up levels as they mature and start hunting prey on a higher trophic level. In a nitrogen study, this would be shown as an increase in nitrogen isotopes of the beak/ hard parts. However, V. infernalis show a decrease in nitrogen isotopes, and therefore trophic levels, throughout its lifespan⁶. This indicates that juveniles are more active and mobile, possibly living in more shallow areas, and become more opportunistic feeders eating detritus in a lower sea level and a more broad area as they mature. This polarity of nitrogen isotopes is backwards of the normal cephalopod lifespan.

Unique Reproductive Cycle

Extant coleoid cephalopods exhibit a semelparous reproductive cycle, going through only one large reproductive cycle immediately followed by death. V. infernalis, once again the exception to their taxonomic class, are iteroparous, and go through over 20 reproductive cycles during their lifetime.

An experiment⁴ examining female V. infernalis specimen found these 20+ repeated cycles consisted of stages of egg spawn, a gonadal resting state, and the development of new eggs. The gonadal resting stage is when the female reproductive organs return to a dormant stage between the spawn of their eggs and the development of new eggs- a feature commonly found in fish, but not present in any extant cephalopod.

The most advanced female individual found in this experiment had 38 spawning events, releasing at least 3,800 eggs, while retaining oocytes for another ~65 spawning episodes (assuming a spawn batch size of 100 eggs).

What is the Significance of the Gonadal Resting Stage?

Most cephalopods are predatory hunters, and get high calorie meals, as well as express a relatively high metabolism. This allows for them to grow fast and put large amounts of energy into reproducing at the end of their life. On the other hand, V. infernalis growth is limited by their hypoxic environment, causing them to have a low caloric intake and low metabolism in order to survive. They can't put all their energy into an extravagant reproductive event. The gonadal resting stage allows for resource and energy accumulation for each egg spawn. The time of this gap is unknown, but estimated to be at least a month long. It also allows for a relatively small amount of energy expenditure towards reproduction.

⁴B. Subadult female who hasn't spawned eggs, only has developing eggs

⁴C. Adult female preparing to spawn eggs showing previously spawned eggs (on right side of graph)

⁴Slow rate of reabsorption of post-ovulatory follicles allow scientists to see the recently spawned egg cycle

Fin-base photophores covered by skin

Skin retracted, exposing fin-base photophores

Epidermal photophores (and eye)

Bioluminescent Display

V. infernalis are believed to have three types of light-emitting organs: large complex photophores at the base of their fins, two clusters of composite organs dorsally behind their eyes, and small, poorly developed photophores scattered across their entire body. A study⁵ has found the composite organs are most likely just extraocular photoreceptors, and there hasn't been observed light emission from the epidermal organs, even though light-producing chemicals have been found in epidermal tissue. In 2003, two new forms of light production were discovered⁵- blue bioluminescence at the tips of all 8 arms, as well as a luminous mucus which is ejected from the distal ends of the arms.

It was found that during handling, the tips of the V. infernalis arms would light up, and with stronger contact stimulus, the individual would eject a glowing, viscous, sticky mucus, which glowed for up to 10 minutes. It is now known that the photophores at the fin bases, lights at the tips of the arms, and glowing mucus ejection work in tandem as a defense mechanism.

Bioluminescent Defense Sequence

In the depths of the ocean where light doesn't penetrate, ink sacs aren't very helpful in escaping predators. The low muscle mass and metabolism of V. infernalis don't allow them to quickly escape their predators either. So, they have developed a visually stunning defense sequence.

When startled, V. infernalis will invert their webbing over their body, exposing their scary-looking (but harmless) cirri, in a pose called the "pineapple posture". While doing this, the tips of their arms will glow a bright blue and aggregate around the photophores at the base of the fins, and the skin normally covering the photophores retract like a pair of eyelids, exposing bright blue spheres which look like glowing eyes.

When a predator approaches, the V. infernalis will have the photophores face the predator to make it appear as it is staring at its predator. Then, the skin will slowly close around the photophores, to decrease their size, making it appear as individual is swimming away, until all the lights are turned off and it disappears into the darkness. There is an animation of this process here. Other instances, during the pineapple posture, the individual ejects a glowing mucus, which sticks to the predator and glows for up to 10 minutes. This confuses the predator, allowingV. infernalis to escape via jet propulsion, at speeds of 2 body lengths/ second for up to 5-10 seconds.

⁵Tip of arms where glowing mucus is ejected from

Flashing fin-base photophores resembling eyes

Pineapple posture

Pineapple pose with glowing arm tips and fin-base photophores

Pineapple posture with visible fin-base photophores

References

1) Department, F. A. O. F. (2022, December 1). Cephalopods of the world. an annotated and illustrated catalogue of cephalopod species known to date. Retrieved December 5, 2022, from https://www.fao.org/3/a0150e/a0150e00.htm

2) Golikov, A. V., Ceia, F. R., Sabirov, R. M., Ablett, J. D., Gleadall, I. G., Gudmundsson, G., Hoving, H. J., Judkins, H., Pálsson, J., Reid, A. L., Rosas-Luis, R., Shea, E. K., Schwarz, R., & Xavier, J. C. (2019). The first global deep-sea stable isotope assessment reveals the unique trophic ecology of vampire squid vampyroteuthis infernalis (Cephalopoda). Scientific Reports, 9(1). https://doi.org/10.1038/s41598-019-55719-1

3) Hoving, H. J., & Robison, B. H. (2012). Vampire Squid: Detritivores in the oxygen minimum zone. Proceedings of the Royal Society B: Biological Sciences, 279(1747), 4559–4567. https://doi.org/10.1098/rspb.2012.1357

4) Hoving, H.-J. T., Laptikhovsky, V. V., & Robison, B. H. (2015). Vampire Squid reproductive strategy is unique among coleoid cephalopods. Current Biology, 25(8). https://doi.org/10.1016/j.cub.2015.02.018

5) Robison, B. H., Reisenbichler, K. R., Hunt, J. C., & Haddock, S. H. (2003). Light production by the arm tips of the deep-sea cephalopodvampyroteuthis infernalis. The Biological Bulletin, 205(2), 102–109. https://doi.org/10.2307/1543231

6) Seibel, B. A., Thuesen, E. V., & Childress, J. J. (1998). Flight of the vampire: Ontogenetic gait-transition in Vampyroteuthis infernalis (Cephalopoda: Vampyromorpha). Journal of Experimental Biology, 201(16), 2413–2424. https://doi.org/10.1242/jeb.201.16.2413

7) Stephens, P. R., & Young, J. Z. (1976). The statocyst of vampyroteuthis infernalis (Mollusca: Cephalopoda). Journal of Zoology, 180(4), 565–588. https://doi.org/10.1111/j.1469-7998.1976.tb04704.x

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