No common name

Gastrocotyle trachuri

ORDER

Polyopisthocotylea

FAMILY Gastrocotylidae

TAXONOMY

Gastrocotyle trachuri van Beneden and Hesse, 1863.

OTHER COMMON NAMES

None known.

PHYSICAL CHARACTERISTICS

Oncomiracidia and early post-larvae are symmetrical; however, 25-35 clamps develop on one side of body, producing a strongly asymmetrical adult that may exceed 0.15 in (4 mm) in length. Small terminal (posterior) flap bearing hamuli and hooklets. Mouth terminal located at one end; buccal cavity encloses two buccal suckers. No sticky pads or eversible sacs. No eyes. Small pharynx. Testis follicular. Muscular penis bulb with penis tube and ring of spines.

DISTRIBUTION

Likely to be present wherever its specific host the scad Trachu-rus trachurus occurs, but not systematically mapped.

HABITAT

Attaches to secondary gill lamellae of Trachurus trachurus by clamps. Single row of clamps attaches to the upstream, outer (efferent) region of secondary lamellae; body then drifts downstream between hemibranchs. Gill ventilating current washes only one side of parasite, promoting asymmetrical development. Asymmetry may be on either the right or left side, depending on which side of primary lamella the parasite attaches itself.

BEHAVIOR

Clamps close, not by suction, but by relatively simple mechanical arrangement. Tendon from single muscle threads through hole in supporting sclerite of one jaw and attaches to other jaw. When muscle contracts, jaws are drawn together. Adult parasite probably unable to change its site on the gill.

FEEDING ECOLOGY AND DIET

Feeds on blood.

REPRODUCTIVE BIOLOGY

Male copulatory organ probably serves for hypodermic (through the skin) impregnation. Infection of scad takes place on sea bottom; in summer at Plymouth, U.K., however, scad become planktonic. Parasites appear to anticipate this change either by ceasing to lay eggs or by laying eggs that enter diapause. Reproductive behavior of parasites may be controlled by hormonal changes in the host. The parasite has access to these hormonal changes via its blood meals.

CONSERVATION STATUS

Not threatened.

SIGNIFICANCE TO HUMANS None known. ♦

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