Entobdella soleae van Beneden & Hesse, 1864; Johnston, 1929.
OTHER COMMON NAMES None known.
Adults 0.07-0.23 in (2 -6 mm) long. Body white or yellowish, flattened with disc-shaped haptor. Embedded in haptor: two pairs of hamuli; one pair of central accessory sclerites that may represent a modified central pair of hooklets; and 14 tiny peripherally located hooklets. Mouth on ventral surface. Conspicuous glandular pharynx. Four eyespots. Adhesive pad on each side of head. Two testes and a large muscular unarmed "penis."
Not systematically mapped. Parasite of common sole, Solea solea, sand sole, Pegusa lascaris and Senegalese sole, Solea sene-galensis on eastern Atlantic seaboard of Europe.
Adult parasites on lower surface of sole. Fifty percent of common soles off English coast carry 1-6 adult parasites.
Body muscles generate haptor suction by lifting anterior pair of hamuli relative to accessory sclerites. Edge of haptor sealed by valve. Soles partly bury themselves in sediments with low levels of oxygen; parasites respond to this condition by undulating their bodies. Their flat bodies also spread and become thinner. These responses increase the availability of oxygen to the organism and enhance its uptake. Adults and juveniles orientate themselves with respect to the host's scales, most probably using their sense of touch. May use scales as clues when moving forward along the upper surface of the host. Movement achieved by alternately attaching the haptor and the sticky pads.
FEEDING ECOLOGY AND DIET
Feed on host's epidermis, which is eroded by the parasite's protrusible pharynx.
Mutual exchange of spermatophores occurs. Parasite lays tetrahedral eggs, each with long stalk. Two eggs laid per hour at 53°F (12°C). Eggs attach to sand grains— not to fish— by sticky droplets on stalks. After incubation for 4 weeks at 53°F (12°C), eggs hatch soon after dawn in absence of host. Host is
nocturnal and rests during daylight; hence freshly hatched larvae have a stationary target. There is, however, an unknown ingredient in the mucus of the sole's skin that stimulates hatching at any time of day or night. Oncomiracidia usually attach to sole's upper surface and migrate forward, moving from the head to the host's lower surface where they reach sexual maturity. When two fishes make contact, adult and juvenile parasites may move from the lower surface of one fish to upper surface of the other. Parasites arriving on the recipient host find their way forward and move onto its lower surface.
CONSERVATION STATUS Not threatened.
None known as of 2003. Entobdella, however, has the potential to kill soles by superinfection in captive situations. Its close relative Neobenedenia melleni poses an especially serious threat to fish farms and aquaria, because it combines the potential for massive superinfections with a remarkably low specificity. Neobenedenia melleni is capable of infecting over a hundred wild and captive fish species belonging to more than 30 families from 5 different orders. ♦
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