Aplysia dactylomela

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Geographic Range

Aplysia dactylomela is found world wide in tropical to warm temperate waters. (Barnes, 1963)

Habitat

Aplysia dactylomela is commonly found in sea grass beds where it feeds. (Barnes, 1963)

  • Range depth
    intertidal to 20 m
    to 65.62 ft

Physical Description

Aplysia dactylomela is generally a pale yellow to green color, though this varies greatly with the food that they consume, as they may be more orange if their diet consists primarily of red algae. A characteristic that differentiates A. dactylomela from others in its genus is the irregular black rings that cover its body. The dorsal surface of the mantle and parapodia are marked with irregular black blotches forming incomplete rings, while the remainder of its body is marked with more complete rings. The foot is broad and well developed, its anterior end is rounded, and the posterior end is more bluntly pointed. The foot has a rough texture, in contrast to the smooth soft surface of the rest of its body. The parapodia are an extension of the foot, in A. dactylomela they are high and thin, allowing the animals to swim in the water column. A reduced shell is covered by the mantle and the gills are located on the right side of the mantle between the shell and the right parapodia. (Borradaile and Potts, 1932; MacFarland, 1909)

Development

The eggs of Aplysia dactylomela are frequently seen in grass beds, intertidal to approximately three meters deep; they appear as a long tangled string of variably shaded green or brown. The large number of eggs produced requires that there be little yolk, early development to the veliger stage, and a long, one month stay in the plankton. Following this veliger stage, the larvae settle on algae where they grow and metamorphose. They continue to feed and grow to sexual maturity. The red algae, Laurencia has been shown to trigger veliger metamorphosis. All of the above were conducted under laboratory conditions. (Stancyk, 1979; Thompson and Brown, 1984)

Reproduction

In laboratory conditions, Aplysia dactylomela has a single reproductive period characterized by repeated spawning. Their first spawn takes place when they are roughly two months old and continues every two to four days until the end of their reproductive cycle roughly seven months later. They continue to feed and grow until they reach a maximum size. At this time they have also reached their peak spawn production. Throughout their seven month reproductive period each adult can produce an estimated 67 million eggs. (Stancyk, 1979)

Like all species of Aplysia, A. dactylomela is hermaphroditic. The male genital opening lies just below the base of the right anterior tentacle, positioned between the right eye and the right side of the mouth. A strongly defined ciliated groove extends dorsally backward from male genetalia between the parapodia to the hermaphroditic orifice, which is marked by a dark depression. The groove is marked by a narrow black line stretching from the male genital opening to the hermaphroditic duct. When mating, one A. dactylomela, acting as a male will climb partially onto a second A. dactylomela, acting as a female, insert the male genetalia and releasing sperm into the hermaphroditic duct of the second. In this manner they form chains of up to 12 organisms, each acting as male and female simultaneously, the first in the chain acting only as a female, and the last acting only as a male. (MacFarland, 1909)

  • Breeding season
    7 months
  • Average number of offspring
    67,000,000
  • Average age at sexual or reproductive maturity (female)
    2 months
  • Average age at sexual or reproductive maturity (male)
    2 months

These animals invest very little in each offspring. Individual eggs receive relatively little yolk, and there is no investment in offspring once the fertilized eggs are laid.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female

Lifespan/Longevity

Following their peak spawn and maximum size A. dactylomela begins to lose weight and spawning declines, death soon follows. (Stancyk, 1979)

  • Average lifespan
    Status: captivity
    10 to 11 months

Behavior

In the adult stage, Aplysia dactylomela is a nocturnal organism, and moves about only after dark. This locomotion can be in two forms, swimming in the water column and crawling on the substrate. Swimming is achieved by folding the parapodia forward and down to create a funnel that pulls in water, pressing the anterior parts of the parapodia together forces the water out behind the animal and it is propelled forward. The more common crawling motion is known as contractive wave motion and is achieved by raising the leading edge of the foot and stretching it forward in an arching pattern; the rest of its body follows the arching pattern until it reaches the tail.

Larval veligers of this species are planktonic, they swim in the open water. (Farmer, 1970; Stancyk, 1979)

Food Habits

Aplysia dactylomela feeds on red and green algae. It uses its jaws to grasp the algae and its radula to pull the algae into its buccal cavity. The crop in A. dactylomela is lined with chitinous plates and acts like a gizzard to aide in the digestion of the larger seaweeds that it eats.

Foods eaten: Chondrococcus hornemanni, Ulva reticulata, Laurencia spp., Martensia fragilis and Spyridia filamentosa. (MacFarland, 1909; Wilbur and Yonge, 1966)

  • Plant Foods
  • algae

Predation

When feeling threatened A. dactylomela will elicit a quick downward movement of its parapodia over its back. It may also release foul fluids from both the opaline gland and the purple dye cavity.

The idea that A. dactylomela releases ink and opaline in defensive situations is widely held. Much of this ascription is based on electroneurophysiological studies. However, further studies were unable to confirm that inking was due to interaction with a predator. (Barnes, 1963; Tobach, et al., 1989; Wilbur and Yonge, 1966)

Ecosystem Roles

This species is one of many that graze on algae in shallow warm water.

Economic Importance for Humans: Positive

Aplysia dactylomela has very large ganglion nerve cells, specifically of interest is the right giant neuron located in the abdominal ganglion. This neuron is very similar to those in vertebrates, making them good subjects for electrophysiological studies as well as conditioned responses. These neurons are valuable for neurological research, as long lasting changes in neuronal behavior can be detected on the level of a single cell as a result of repeated and concommitant pairing of two inputs. (Corning and Dyal, 1973)

  • Positive Impacts
  • research and education

Conservation Status

This species is fairly abundant and not believed to need any special conservation efforts.

Contributors

Renee Sherman Mulcrone (editor).

Melissa Emore (author), Hood College, Maureen Foley (editor), Hood College.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

year-round breeding

breeding takes place throughout the year

References

Australian Museum, 2004. "Wildlife of Sydney" (On-line). Sea hare fact file. Accessed July 16, 2004 at http://www.faunanet.gov.au/wos/factfile.cfm?Fact_ID=43.

Barnes, R. 1963. Invertebrate Zoology. Philadelphia/London: W.B. Saunders Company.

Behrens, D., M. Behrens. 1999. "Applysia dactylomela" (On-line). The Slug Site -- Opistobranch of the Week. Accessed July 16, 2004 at http://slugsite.us/bow/nudwk174.htm.

Borradaile, L., F. Potts. 1932. The Invertebrata, A Manual for the Use of Students. London: Cambridge University Press.

Corning, W., J. Dyal. 1973. Invertebrate Learning: Volume 2. New York: Plenum Press.

Farmer, W. 1970. Swimming gastropods (opisthibranchia and prosobranchia). The Veliger, 13; No. 1: 73-89.

MacFarland, F. 1909. The Opisthibranchiate Mollusca of the Branner-Agassiz expedition to Brazil. California: Stanford University.

Stancyk, S. 1979. Reproductive Ecology of Marine Invertebrates. Columbia, South Carolina: University of South Carolina Press.

Thompson, T., G. Brown. 1984. Biology of Opisthobranch Molluscs, Volume 2. London: British Museum of Natural History.

Tobach, E., A. Zaferes, L. Migenis-Lopez. 1989. Aplysia ink and opaline: exploration of their relation to predation. Bulletin of Marine Science, 45: 664-670.

Wilbur, K., C. Yonge. 1966. Physiology of Mollusca: Volume 2. New York: Academic Press.