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Phestilla sibogae

By Terri Nelson

Geographic Range

This species is found in the tropical portions of the Indian and western Pacific Oceans, and probably ranges from Panama west to Africa.

Habitat

Phestilla sibogae lives in tropical marine environments amongst coral reefs. Because of its utter dependence on its prey, P. sibogae is always found on or near colonies of coral in the genus. (Gochfield and Aeby, November 1997; Gochfield and Aeby, November 1997; Gochfield and Aeby, November 1997)

  • Aquatic Biomes
  • reef

Physical Description

This species grows to be 30-40 mm long.

Like all nudibranchs, this species lacks the shell, gills and mantle cavity that most other snails have. Nudibranchs have flaps or fins on the lateral sides of the foot, called parapodia. These structures allow the animals to swim. Respiration occurs through the epidermis of the dorsal body wall. Phestilla sibogae exhibits external bilateral symmetry, although some internal organs are slanted to the right (called detorsion). It has a complete digestive system, with the anus located at its posterior.

Phestilla sibogae is very well camouflaged on Porites coral and is difficult to see there. (Bertsch and Johnson, 1981; Boudko, et al., January 5, 1999; Grzimek, 1972; Morton, 1979; Murphy and Hadfield, November 1997)

Like many other nudibranchs, P. sibogae has two sets of tentacles, called anterior sensory organs, on its head. One of the sets of tentacles, called rhinophores, are located on the dorsal side and are about 5 mm long. The rhinophores specifically are implicated in olfaction and sensing the presence of prey, possible predators, and members of the same species. The slightly flattened looking oral tentacles extend from the mouth area and are 5-7 mm long. The nerves of these structures both connect to the cerebral ganglia. The brain of this species consists of three pairs of fused sections; the cerebral ganglia, the pleural ganglia, and the pedal ganglia. The neurons are large and easily identifiable.

Also found on the head are slender extensions called cerata, which aid in gas exchange. Unlike other nudibranchs, P. sibogae does not store the nematocysts (stinging organelles) of its prey in its cerata. (Bertsch and Johnson, 1981; Boudko, et al., January 5, 1999; Grzimek, 1972; Morton, 1979; Murphy and Hadfield, November 1997)

The larval stage of P. sibogae, called a veliger, has a transparent, caplike shell and an operculum not found in adult individuals. The velum, which the larvae use to swim and feed, are bilobed and ciliated around their mouths. The velum is reabsorbed along with the shell during metamorphosis. (Bertsch and Johnson, 1981; Boudko, et al., January 5, 1999; Grzimek, 1972; Morton, 1979; Murphy and Hadfield, November 1997)

  • Range mass
    0.8 to 1.7 g
    0.03 to 0.06 oz
  • Range length
    30 to 40 mm
    1.18 to 1.57 in

Development

Reproduction

Phestilla sibogae is a simultaneous hermaphrodite; this means that both male and female reproductive organs are present and mature at the same time. Two individuals mate and cross-fertilize each other. Mating can occur before the individual is mature enough to lay eggs, so sperm may be stored until later.

Individuals reach maturity when they are 15-25 mm long. The eggs are then laid in one session of repeated spawning. The eggs have an egg membrane and a covering of albumen. Masses of them are enclosed together in a cylinderical cord covered with a thick layer of mucus for protection. The long, gelatinous loops of eggs resemble ribbons.

The free-swimming planktonic larvae are called veligers. They hatch and begin to feed on other plankton approximately five days after fertilization. Seven to ten days after hatching, they are physically able to metamorphose. Porites releases a chemical which induces the larvae to settle on it and begin metamorphosis.

The species grows and reproduces fairly rapidly, with about forty days between generations. (Bertsch and Johnson, 1981; Morton, 1979; Murphy and Hadfield, November 1997; Pires, et al., June 2000; Todd, et al., 1997)

  • Parental Investment
  • no parental involvement

Behavior

Once it has settled on a Porites coral, adult P. sibogae tend to keep a low profile. During the day they hide among coral branches to avoid being seen by predators, venturing out only at night to feed on the coral branches. Many P. sibogae usually live in the same coral colony. P. sibogae follow slime trails left by others to and from reproductive sites. (Gochfield and Aeby, November 1997)

Communication and Perception

Phestilla sibbogae follow slime trails left by others to and from reproductive sites. (Gochfield and Aeby, November 1997)

Food Habits

Phestilla sibogae is a corallivore, a specialized predator which feeds only on corals. This species feeds only on the genus Porites. Phestilla sibogae senses its prey through distance chemoreception. Epithelial tissue on the rhinopores is sensitive to amino acids released by Porites corals, allowing recognition. Phestilla sibogae then scrapes its radula, a flexible tongue-like membrane with two or three rows of teeth, across the coral surface to draw food into its mouth.

The species is a ravenous eater, and were it not for predatory control by several reef crustaceans and fishes, they would quickly eat their way through an entire reef. An adult P. sibogae can eat up to 6.4 square centimeters of coral each day. (Bertsch and Johnson, 1981; Boudko, et al., January 5, 1999; Gochfield and Aeby, November 1997; Murphy and Hadfield, November 1997)

  • Animal Foods
  • cnidarians

Predation

Various species of reef-dwelling crustaceans and fish eat this species of nudibranch. It avoids some predators by hiding during daylight and only moving around at night.

Economic Importance for Humans: Positive

Phestilla sibogae's primitive brain and nervous system with easy to identify neurons make it useful in neural research. (Boudko, et al., January 5, 1999)

Economic Importance for Humans: Negative

Phestilla sibogae has no negative affect on humans. Their possible negative effects on coral populations are generally kept in check by predators, however, human disturbance of predator populations could initiate severe coral damage by P. sibogae. (Gochfield and Aeby, November 1997)

Conservation Status

There are no accurate figures as yet about the populations of P. sibogae. However, factors that affect the health of the coral reefs they live in such as chemical pollution, silt, or human disturbance would obviously affect the health of P. sibogae populations.

Other Comments

As the state of the world's coral reefs becomes more and more in danger, some people have suggested that scientists attempt to transplant coral to severely damaged spots. Research on P. sibogae indicates that if it had no natural predators, it would continue to reproduce and eat Porites coral until it was gone. If such an idea were put into practice, we would first need an in depth understanding of the components of the ecosystem, including species that hold predators of other species in check. (Gochfield and Aeby, November 1997)

Contributors

Renee Sherman Mulcrone (editor), George Hammond (editor), Animal Diversity Web.

Terri Nelson (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

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.

chemical

uses smells or other chemicals to communicate

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

ectothermic

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

fertilization

union of egg and spermatozoan

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

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.

oviparous

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

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

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

sedentary

remains in the same area

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

tropical

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

References

Bertsch, H., S. Johnson. 1981. Hawaiian Nudibranchs. Honolulu, Hawaii: Oriental Publishing Co..

Boudko, D., M. Switzer-Dunlap, M. Hadfield. January 5, 1999. Cellular and subcellular structure of anterior sensory pathways in Phestilla sibogae. Journal of Comparative Neurology, 403: 39-52. Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10075442&dopt=Abstract.

Gochfield, D., G. Aeby. November 1997. Control of populations of the coral-feeding nudibranch phestilla sibogae by fish and crustacean predators. Marine Biology, 130: 63-69. Link to paper at http://link.springer.de/link/service/journals/00227/papers/7130001/71300063.pdf.

Grzimek, B. 1972. The Gastropods. Pp. 112-118 in Grzimek's Animal Life Encyclopedia. London: Litton World Trade Corporation.

Hadfield, M. 2001. "From finding the right home to metamorphosis: How do invertebrate larvae do it?" (On-line). Accessed April 23, 2003 at http://www.scienceinafrica.co.za/2001/september/larvae.htm.

Kewalo Marine Laboratory, M. unknown. "Reproductive Data for Phestilla sibogae (Bergh)" (On-line). Accessed April 23, 2003 at http://www.pbrc.hawaii.edu/db/rowitem.cgi?row=129.

Morton, J. 1979. Molluscs. London: Hutchison & Co. (Publishers) Ltd..

Murphy, B., M. Hadfield. November 1997. Chemoreception in the nudibranch gastropod Phestilla sibogae. Comparative Biochemistry and Physiology: 727-735.

Pires, A., R. Croll, M. Hadfield. June 2000. Catecholamines modulate metamorphosis in the opisthobranch gastropod Phestilla sibogae. Biological Bulletin, 198:3: 319-331. Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10897446&dopt=Abstract.

Todd, C., M. Hadfield, W. Snedden. 1997. Juvenile mating and sperm storage in the tropical corallivorous nudibranch Phestilla sibogae. Invertebrate Biology, 116: 322-330; Abstract at http://www.invertebratebiology.org/ib1164.htm#A1.6.

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