Parorchis acanthus (Nicoll, 1906)

Dronen, Norman O., Blend, Charles K., Gardner, Scott L. & Jiménez, F. Agustín, 2007, Stictodora cablei n. sp. (Digenea: Heterophyidae) from the royal tern, Sterna maxima (Laridae: Sterninae) from Puerto Rico and the Brazos County area of the Texas Gulf coast, U. S. A., with a list of other endohelminths recovered in Texas, Zootaxa 1432 (1), pp. 35-56 : 53

Parorchis acanthus (Nicoll, 1906)

Locality: Bryan Utility Lake , Bryan, Brazos County, Texas, U.S.A., 30° 24’ N latitude, 96° 13’ W longitude .

Site of infection: Cloaca.

Deposited specimens: Voucher specimens (1 specimens) HWML 48503 .

Prevalence: 1of 4 birds, 25%.

Mean intensity: 3 individuals/infected bird.

Basic comparative description: Based on 2 adult specimens. Body oval, spinose, 3,125 (3,000 –3,250) long by 1,825 (1,745 –1,905) wide with head collar bearing a single row of spines; forebody 725 (630–820) by 1,100 (1,050 –1,150). Mouth subterminal; oral sucker 280 (240–320) by 370 (315–425); prepharynx absent; pharynx longer than wide, 200 (190–210) by 150 (125–175); esophagus 320 (295–345); ceca long, terminating near posterior extremity. Acetabulum large, 720 (695–745) by 800 (755–845). Testes side by side, deeply lobed, near posterior extremity; left testis 410 (345–475) by 350 (310–390); right testis 450 (425–475) by 320 (290–350). Genital pore immediately anterior to acetabulum near midline of body; cirrus sac relatively short, external seminal vesicle sac overreaching the acetabulum posteriorly, extending some distance into hindbody. Ovary oval to round, situated immediately anterior to intertesticular space near midline of body, 280 (245– 315) by 240 (220–260). Eggs operculate, 60 (56–68) by 31 (30–35). Excretory pore terminal.

Remarks. Parorchis acanthus is a relatively common fluke found in the cloaca of aquatic birds in North America and elsewhere in the world. Although it has been raised experimentally in S. maxima by Williams (1969), this is the first report of a naturally infected royal tern.