Oyster leech

Stylochus inimicus

ORDER Polycladida

FAMILY Stylochidae

TAXONOMY

Stylochus inimicus Polombi, 1931, Florida, United States.

OTHER COMMON NAMES None known.

PHYSICAL CHARACTERISTICS

Body is oval or discoid with retractile nuchal tentacles; marginal eyes in band, cerebral and tentacular eyes present; pharynx long in middle of body, intestinal branches not anastomosing; male and female gonopores close to each other in posterior of body.

DISTRIBUTION Florida, United States.

HABITAT

Under rocks and algae and in oyster shells and other invertebrates.

BEHAVIOR

Tends to hide under debris or in shells of oysters and barnacles.

FEEDING ECOLOGY AND DIET

Carnivorous feeding on animal matter, including oyster tissue. Hypsoblennius, a small blenny, has been shown to feed on it.

REPRODUCTIVE BIOLOGY

Following mating, which may last nine hours and involve more than four partners, an individual can deposit 7,000-21,000 eggs (0.007 in [0.18 mm]) during a summer month. Egg masses usually attached to clean oyster shell and irregular in shape and only one layer thick. Worms observed covering eggs, protecting them. Ciliated larvae with six eyes hatch from eggs. Positively phototactic, causing them to swim up and away from the bottom helping them to disperse.

CONSERVATION STATUS

Not threatened.

SIGNIFICANCE TO HUMANS

Observed entering, devouring, and killing oysters. It has been blamed for the large oyster kill in Florida in 1932-1933. However, it is likely that other environmental factors were also compromising the oysters. The eradication of the worms from oyster beds is difficult; it has been suggested that flooding with freshwater may control worms. ♦

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