Form and Function

Aplysia dactylomela is typically a pale yellow to green color although specimens with different coloring schemes are not all that uncommon (Encyclopedia of Life 2008). The distinguishing characteristic of A. dactylomela comes from the ring-like irregular splotches on the dorsal portion of the its body, netting it the common name of "spotted sea hare" (Encyclopedia of Life 2008). Suprisingly compared to the size of terrestrial snails that most people are familar with, A. dactylomela typically grows to 15 or 16 centimeters as an adult with a maximum size of 40 centimeters (Marine Invertebrates of Bermuda 2008 , Encyclopedia of Life 2008). Moving on from these basic distinguishing features of A. dactylomela, for organizational purposes, the following paragraphs will divide the organism into three sections—body plan and locomotion, sensory organs and neurology, and digestive system structure and options for food—to more easily explain the form and function of the animal. Although it could potentially belong within this page, please be aware that the purple gland and the inking ability of A. dactylomela will be covered in the "Interaction with Other Species" section so head over to that portion of the website if it is your primary interest.

Like the majority of other Opisthobranch mollusks, A. dactylomela contains a thin, barely calcified, shell in the interior of its body that might give some support but provides nowhere near the protection of other mollusks like clams. Instead, A. dactylomela, its relatives, and ancestors developed large flaps of skin that attach near the foot and can fold over the mantle to protect the gill and other organs previously defended by a shell (Sea Slug Forum 2000). Some Opisthobranchs use the parapodia to swim gracefully through the water, but since A. dactylomela's is relatively small in comparison, it can only swim for brief periods at a time (Marine Invertebrates of Bermuda 2008). Alternatively, the large muscular foot, located along the entirety of its mantle, provides the majority of its locomotion, unless prompted to swim by some stimuli like predation. Compared to the rest of the organism's skin that has a leathery, smooth texture, the foot feels rough and likely helps by providing traction (Encyclopedia of Life 2008)(Sea Slug Forum 2000).

The term 'sea hare' comes from the non-scientific grouping of sea slugs with tentacles that resemble rabbit's ears, thus making them look like rabbits of the sea. What would be the rabbits ears is instead a pair of sensory organs called rhinophores which are very similar in function to a nose in that it allows the sea hare the ability to smell food and pheromones from other A. dactylomela. Just below the rhinophores on the head of the sea slug are the eye. While they are far from being able to distinguish objects, they can see some light. A. dactylomela is a nocturnal animal and these eyes help detecting safe times for searching for food as well as when a predators might be nearby by the shadow it casts. On either side the creatures mouth are the oral tentacles, and in combination with the rhinophores allow the slug smell and taste(Sea Slug Forum 2000). Controlling all the organisms functions are multiple simple clusters of nerves called ganglion which are sort of like an incredibly simple brain.

Aplysia dactylomela is a herbivore that dines primarily on green and red algae, but can also eat larger sea weeds as well. Using the array of tentacles described above as a locator, Aplysia dactylomela pull itself through the shallow water grass sea beds with its muscular food. Once food is found found, A. dactylomela dines by using its jaws to clutch the meal and radula to suck the food into its buccal cavity. From there, the crop’s chitinous plates that act like a gizzard, helping digest larger weeds and masses of algae (Encyclopedia of Life 2008). Moving farther into the digestive system, food and other particles enter the stomach and eventually either the intestines or caecum, all of which have ciliated walls that complete a complicated sorting of edibles from non-edibles (Sea Slug Forum 2000). One interesting aspect of Aplysia dactylomela's diet is its influence on the coloring of the organism and the ability to swim; a diet consisting mostly of red algae can have the effect of coloring the slug a darker red while a diet heavy in silicone can prevent the slug from being able to float well and thus, swim (Marine Invertebrates of Bermuda 2008). 

Up next: Learn more about the reproduction of A. dactylomela.