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Entobdella soleae

By Kunal Chaudhary and Brandon Zurawlow

Geographic Range

Entobdella soleae is a monogenean flatworm and an ectoparasite of the common sole (Solae solae). As such, its range is limited to geographic areas inhabited by the common sole, mostly in the eastern Atlantic Ocean from Norway to Senegal and in the Mediterranean Sea. The common sole is frequently harvested for food in Europe, and a large number of parasitic infections by E. soleae have been reported in captivity. (Harris and Bray, 2012; Kearn, 2002)

Habitat

Entobdella soleae is generally found in temperate, marine environments high in host availability. Entobdella soleae has extremely high host exclusivity, with literature citing only three possible host species, all within genus Solae, with a strong preference for Solae solae over other soleid fish. Solae solae is most commonly found hidden within the sand or mud in shallow waters. While larvae may initially be free-swimming, adults live exclusively on the skin of the host. A free-swimming larva will attach to the dorsum of the host and migrate toward the host's ventral surface, which is in contact with the sea floor, where it completes development and reproduces. (Kearn and Evans-Gowing, 1998; Kearn, 1967; Kearn, 2002; Sukhedo and Sukhedo, 2002)

  • Range depth
    0 to 152 m
    0.00 to 498.69 ft

Physical Description

The average size of Entobdella soleae has not been clearly defined in the current literature. However, studies reference specimens of 2 to 6 mm in length. Entobdella soleae exhibits the typical monogenean body plan. It is flat, translucent, and has a large, disc-shaped haptor, a posterior organ used for semi-permanent attachment to the host. A distinguishing feature of the organism is its unique prohaptor, an anterior structure with two adhesive pads. These adhesive pads secrete a strong cement that temporarily attaches the organism to a substrate and are critical for locomotion. (El-Naggar and Kearn, 1983; Kearn and Evans-Gowing, 1998; Kearn, 1963a; Kearn, 1963b; Kearn, 2002)

  • Range length
    2 to 6 mm
    0.08 to 0.24 in

Development

The life cycle of Entobdella soleae is largely dependent on the presence and hypoactivity of a host sole. Individuals secured to the lower surface of the host lay eggs that become secured to the substrate via a sticky coating. This prevents the eggs from being taken away from a population of hosts by currents should the parental host change location. After approximately a month of development, larvae emerge from the egg within 5 minutes of being activated by an environmental stimulus. Studies suggest that the hatching of the eggs is rhythmic with respect to light and that sole mucous or urea activate the embryos. The larval form that hatches from the egg is referred to as an oncomiracidium. This free swimming larvae locates a host; attachment may occur as quickly as 2 minutes after hatching and must be completed within 24 hours, before the oncomiracidium depletes its energy and dies. The oncomiracidium attaches to the host’s upper anterior surface before migrating to the lower surface. Upon attachment, the parasite sheds its ciliated epidermal cells. The exact duration of the larval stage is not reported in literature. However, it is suggested to last approximately 40 days, the length of time required to complete the migration process to the lower surface of the host where it subsequently reaches sexual maturity. Thus, with the exception of the egg, there is little to no uninfective period throughout the life cycle of E. soleae. (Kearn, 1963a; Kearn, 1963b; Kearn, 1973; Kearn, 2002; Sukhedo and Sukhedo, 2002)

Reproduction

Due to the relatively low population density of Entobdella soleae in the wild, (1 to 3 individuals per host), it has been suggested that there is a mechanism for pheromonal attraction between individuals. This is supported by the fact that there is a layer of stagnant water between the host sole and the sea floor. This small but stable volume of water would allow for pheromones to be transmitted without interruption from current and may be part of the reason that adults migrate to the lower surface of the host. Due to the lack of concrete evidence, however, the exact mechanism for the attraction of mates has yet to be determined. (Kearn, 2002; Kearn, et al., 1993)

Entobdella soleae is a protandrous hermaphrodite that reproduces sexually. Although each organism houses both male and female organs, it is believed that self-fertilization is not possible due to the fact that the male reproductive organs cease to operate at the same time the female reproductive organs become active. Clutch size and gestation period of this hermaphroditic monogenean are highly variable depending on the size of the individual. One study found that medium to large individuals may produce 30 to 60 eggs a day with gestation periods lasting anywhere from 5 seconds to 168 minutes. Additionally, as the size of the organism increases, there is a slight increase in the size of the eggs produced. (Kearn, 1963a; Kearn, 1963b; Kearn, 1985; Kearn, 2002; Kearn, et al., 1993)

  • Range gestation period
    0.08 to 168 minutes

Entobdella soleae does not provide any parental involvement.

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

Individuals of Entobdella soleae have a lifespan of up to 6.5 months. There is no observed difference between those individuals obtained from the wild and those grown in a laboratory setting. (Kearn, 1990)

  • Range lifespan
    Status: wild
    6.5 (high) months
  • Range lifespan
    Status: captivity
    6.5 (high) months

Behavior

Entobdella soleae larvae, or oncomiracidia, are photosensitive early in development and swim to higher areas of the ocean as a result. As the parasites mature (as soon as 30 minutes after hatching), they swim to the ocean floor in order to search for hosts. The attachment of the parasite to the host's epidermis is facilitated by a muscular haptor, which produces a suction between the parasite and host. Unbranched banded fibrils make up the tendons found in the extrinsic muscles of the parasite that create the suction pressure at the distal portion of the haptor. The haptor is roughly 0.5 mm in diameter and consists of hooks and papillae that lock onto the host’s skin. Generally, 1 to 3 adult individuals are found per infected sole, though this number may increase for those in captivity. E. soleae can cause skin inflammation on the flatfish and death. (Kearn, 1964; Kearn, 1980; Kearn, et al., 1993)

Home Range

Adults of Entobdella soleae remain on their hosts. Larvae are free-swimming, but for less than 24 hours, and ideally remain close to possible hosts. (Kearn, 1963a; Kearn, 1963b)

Communication and Perception

Mucus, from the epidermis of the sole, and urea, from the urine of a nearby host, can stimulate eggs to hatch, possibly increasing the chances of larvae to make contact with a host. During the oncomiracidium stage, individuals of Entobdella soleae find their hosts by chemoreception to a substance secreted by the host's mucus cells in its epidermis. A theorized search pattern for hosts is accomplished with the coupling of horizontal transport of larvae by water currents and photopositive and photonegative vertical movements. Photopositive vertical movements become less frequent as the larvae grow older. Larvae have also been shown to find prey in the presence of only infra-red light. It is hypothesized that pheromone attractions allow for early mating among the individuals. (Kearn, 1967; Kearn, 1980; Kearn, et al., 1993)

Food Habits

Entobdella soleae is a skin parasite of Solea solea and uses its pharynx as its feeding organ. There are glands in the pharynx that secrete proteolytic enzymes to digest the epidermis of the flatfish. The pharynx sucks in the digested food in liquid form for absorption in the intestinal diverticula. (Kearn, 1963c)

  • Animal Foods
  • fish

Predation

There are no known predators of Entobdella soleae reported in literature.

Ecosystem Roles

Entobdella soleae is a skin parasite. The host is specific for this monogenean parasite and is Solea solea, a flatfish. In the wild, only a few parasites are found on a given host. In fish farms, a few hundred parasites can be found per fish, causing mass skin inflammation and death. (Kearn, et al., 1993)

Species Used as Host

Economic Importance for Humans: Positive

There are no known positive effects of Entobdella soleae on humans.

Economic Importance for Humans: Negative

Because Entobdella soleae is a skin parasite capable of causing death of its host, Solea solea, this monogenean parasite is an economic hindrance for humans. Solea solea is a versatile fish used in cooking and highly valued for its taste in Europe. (Dinis, et al., 1999)

Conservation Status

Entobdella soleae has no special conservation status.

Contributors

Kunal Chaudhary (author), The College of New Jersey, Brandon Zurawlow (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Angela Miner (editor), Animal Diversity Web Staff.

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

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

ectothermic

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

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

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.

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.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

piscivore

an animal that mainly eats fish

protandrous

condition of hermaphroditic animals (and plants) in which the male organs and their products appear before the female organs and their products

saltwater or marine

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

sexual

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

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

References

Dinis, M., L. Ribeiro, F. Soares, C. Sarasquete. 1999. A review on the cultivation potential of Solea senegalensis in Spain and in Portugal. Aquaculture, 176/1-2: 27-38.

El-Naggar, M., G. Kearn. 1983. Glands associated with the anterior adhesive areas and body margins in the skin-parasitic monogenean Entobdella soleae. International Journal for Parasitology, 13/1: 67-81.

Harris, P., R. Bray. 2012. "Entobdella soleae (van Beneden & Hesse, 1864)" (On-line). World Register of Marine Species. Accessed October 25, 2012 at http://www.marinespecies.org/aphia.php?p=taxdetails&id=119432.

Kearn, G. 1973. An endogenous circadian hatching rhythm in the monogenean skin parasite Entobdella soleae, and its relationship to the activity rhythm of the host (Solea solea). Parasitology, 66: 101-122.

Kearn, G. 2002. Entobdella soleae - pointers to the future. International Journal for Parasitology, 32/3: 367-372.

Kearn, G. 1985. Observations on egg production in the monogenean Entobdella soleae. International Journal for Parasitology, 15/2: 585-605.

Kearn, G. 1963. The egg, oncomiracidium, and larval development of Entobdella soleae, a monogenean skin parasite of the common sole. Parasitology, 53/3-4: 435-447.

Kearn, G. 1963. The life cycle of the monogenean Entobdella soleae, a skin parasite of the common sole. Parasitology, 53: 253-263.

Kearn, G. 1990. The rate of development and longevity of the monogenean skin parasite Entobdella soleae. Journal for Helminthology, 64: 340-342.

Kearn, G., R. Evans-Gowing. 1998. Attachment and detachment of the anterior adhesive pads of the monogenean (platyhelminth) parasite Entobdella soleae from the skin of the common sole (Solea solea). International Journal for Parasitology, 28: 1583-1593.

Kearn, G., R. James, R. Evans-Gowing. 1993. Insemination and population density in Entobdella soleae, a monogenean skin parasite of the common sole, Solea solea. International Journal for Parasitology, 23/7: 891-899.

Kearn, G. 1967. Experiments on host-finding and host-specificity in the monogenean skin parasite Entobdella soleae. Parasitology, 57: 585-605.

Kearn, G. 1963. Feeding in some monogenean skin parasites: Entobdella soleae on Solea solea and Acanthocotyle sp. on Raia clavata. Journal of the Marine Biological Association of the United Kingdom, 43: 749-767.

Kearn, G. 1980. Light and gravity responses of the oncomiracidium of Entobdella soleae and their role in host location. Parasitology, 81: 71-89.

Kearn, G. 1964. The attachment of the monogenean Entobdella soleae to the skin of the common sole. Parasitology, 54: 327-335.

Sukhedo, M., S. Sukhedo. 2002. Fixed behaviors and migration in parasitic flatworms. International Journal for Parasitology, 32: 329-342.

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