Form & Function

Aequorea victoria is commonly described as an umbrella shaped organism.  The top of the organism is known as the umbrella or bell, and the underside of the umbrella is known as the subumbrella (Shimomura, 1999).  It is also motile in its medusa form only (click here for information on medusa life stage).  Understanding the general body plan of a jellyfish like Aequorea victoria is crucial for understanding how the form of the body relates to the function of the organisms structures.

The swimming action of the medusa form is actually quite complicated and unique in Aequorea victoria.  According to a recent study by Dr. Richard Satterlie, Aequorea victoria are capable of utilizing only parts of their muscular swimming tissues at certain times, such as using part of their radial muscle for swimming and feeding at the same time (Satterlie, 2008).  This adaptation could be quite advantageous to the survivability of Aequorea victoria.  For example, if Aequorea victoria needed to stop swimming in order to eat its prey, it may be vulnerable to attacks by predators because it is stationary.

Organisms living in aquatic environments similar to the Pacific Ocean require osmoregulation adaptations, so not surprisingly Aequorea victoria has developed adaptations to survive in differentiating water conditions.  In a study by Dr. Claudia E. Mills, Aequorea victoria and other hydromedusae were put in solutions of higher and lower salinity than normal seawater, lowering and raising water concentrations respectively.  Initially the organisms would float at the surface in lower salt conditions and sink to the bottom in higher salt conditions.  Once Aequorea victoria was able to equilibrate with its new environment, it swam as usual.  However, during this equilibration period the studied hydromedusae, including Aequorea victoria, generally contracted in what could be described as a protective manner analogous to fetal positioning in humans, but soon after resumed normal swimming (Mills, 1984).  These results agree with the osmotic potential that would be present across the cell membranes of Aequorea victoria in these solutions.  This reaction to its enviornment is a behavior in the sense that a stimulus occurred, and the organism adapted to the stimulus before resuming normal function.  These observations not only show that Aequorea victoria is able to adapt to stimuli, but also that it may alter its behavior until normal conditions are restored.  This may be an area for potential further research into the ability of jellyfish like Aequorea victoria to recognize and adapt to enviornmental stimuli.

Figure 1. "Prey tracks around Aequorea victoria in the laboratory. Black tracks: prey that are entrained and encountered (or pass through tentacles); gray tracks: prey not encountered by the medusa" (Kataji et al., 2011).

There is another interesting relationship present in Aequorea victoria between body shape, swimming, and feeding.  Aequorea victoria is classified as having an oblate medusa form.  Oblate means a sphere flattened at the poles similar to the shape of a ball being forcibly stepped on.  This oblate shape has implications for both motility and feeding.  Multiple studies have come to the same convergent conclusion: the swimming pattern of Aequorea victoria is a slow constant motion (Satterlie, 2008; Colin & Costello, 2001).  This process of swimming in Aequorea victoria is characterized as a series of contractions of the circular muscles that surround the bell of the organism (Satterlie, 2008).  These contractions flush water out of the subumbrellar cavity in a manner analogous to jet propulsion (click here for an organism that has developed jet propulsion movement through convergent evolution) creating the slow graceful motion pattern seen in oblate medusae such as Aequorea victoria (Satterlie, 2008; Colin & Costello, 2001).  This slow constant motion creates directional currents due to vortex effects that direct potential food into the trailing tentacles of Aequorea victoria (Kataji et al., 2011; Colin & Costello, 2001).  This vortex phenomenon is clearly visible in Aequorea victoria when tracking water movement around Aequorea victoria as it swims (fig. 1).

Knowledge of the motile stage of Aequorea victoria is important in understanding how the organism feeds in its medusa form, but Aequorea victoria does not always feed while it swims.  For more information about the rest of the life cycle of Aequorea victoria click the Life History Button below.