Euprymna scolopes
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Last Updated 10.23.2005

Euprymna scolopes

Euprymna scolopes, commonly known as the Hawaiian Bobtail Squid, is a very small cephalopod about 33 millimeters long. It is endemic to the waters surrounding the Hawaiian islands and lives in a shallow water (2-4 cm deep) habitat. It is a largely nocturnal animal that buries itself in the sand during the daytime. This hiding behavior is very effective. The squid will nestle itself down into the substrate and use its tentacle arms to pull sand and gravel up over its body, only leaving its eyes bare and uncovered. [Watch a video]. Its life history shows a very short life span, reaching sexual maturity at 2 months and dieing anywhere between 3 and 10 months. It is a semelparous species, reproducing once in its lifetime. It has been suggested that E. scolopes has a high level of neural complexity, on par with more behaviorally advanced cephalopod molluscs (Wood 1999).

In the wild, E. scolopes is commonly predated by the monk seal. It’s main food source is shrimp, although it has been fed brine shrimp, mysids, mosquitofish, octopus and prawns in the laboratory (Wood 1999).

E. scolopes has been studied largely in investigations of its use of bacterial symbionts in bioluminescence. Hypothetically, a better understanding of this type of mutualism could allow geneticists to implant V. fischeri in other organisms and make them luminesce as well. Juveniles are born without bacteria and must acquire them from the sea water. The bilobed light organ of a young squid has ciliated arms that sweep the bacteria into a crypt where they can colonize. Individual crypts are sealed off and the organ will be modified for adulthood, losing the arms. Once the colony has taken up residence, the bacteria mutate, decrease in size, lose their flagella and begin to glow. This process takes several hours and after a few weeks the entire squid has become fully colonized (Graf 2005).

An interesting physiological attribute of the Bobtail squid is their use of extraocular photosensitive vesicles. Jones and Nishiguchi led the first experiment to demonstrate counterillumination by E. scolopes. As an artificial light source was increased and decreased in intensity, each squid adjusted its luminescence accordingly. As downwelling light increased, so did ventral emissions, up to a point where ventral emissions decreased. It was suggested that this pattern illustrated that light emission was controlled in a rapid, practical manner to down-welling light. The reduced emission at high light levels is probably an energy saving device used when counterillumination is no longer effective. It is important to note that counterillumination is still considered a theory, and little research has been done to quantify the reduction in predation of animals that exhibit this behavior. Nevertheless, the phenomenon is fascinating.

Figure (above): Euprymna scolopes Photograped by Roland Anderson.

Figure (left): Euprymna scolopes Photographed by Richard Young.

Figure modified from homepage