Otodistomum hydrolagi sp. n. (Trematoda: Azygiidae) from the Coelom of the Ratfish, Hydrolagus colliei (Lay and Bennett, 1839)

Abstract

Otodistomum hydrolagi sp. n. was obtained from the coelom of 2 ratfish, Hydrolagus colliei (Lay and Bennett, 1839), which were dredged from Puget Sound in the vicinity of San Juan Island, Washington. 0. hydrolagi is the third species of the genus known to inhabit the coelom. The new species bears some resemblance to 0. plunketi Fyfe, 1953, and 0. pristiophori (Johnston, 1902) which also inhabit the coelom of their hosts. Two specimens of a new species of the genus Otodistomum Stafford, 1904, were collected from the coelom of two of 44 ratfish, Hydrolagus colliei (Lay and Bennett, 1839), taken by dredge in the vicinity of San Juan Island, Washington. One specimen was prepared as a stained whole mount. The other, a damaged specimen, was used to prepare serial frontal sections. Measurements are in millimeters unless otherwise indicated. Otodistomum hydrolagi sp. n. (Figs. 1-4) Body light green when alive, fusiform, flat, muscular, nonspinous, 25 long by 10 wide. Oral sucker subterminal, round in ventral view with a diameter of 2; ventral sucker located 5 from anterior end of body, round, with a diameter of 3. Pharynx 0.93 long by 0.6 wide; prepharynx and esophagus absent. Intestinal ceca sinuous, irregular in outline, ending blindly at posterior end of body. Cirrus sac anterior to ventral sucker, oval, 1 long by 0.7 wide, contains curved seminal vesicle and looped prostatic duct; prostatic cells inconspicuous, restricted to widened portion of duct; ejaculatory duct sinuous, extending from cirrus sac to tip of fleshy genital cone; cirrus absent. Testes in midbody region, opposite, triangular in ventral view, 0.8 long by 1.1 to 1.4 wide. Vasa efferentia pass dorsal to uterine folds and join short vas deferens near cirrus sac. Ovary immediately pretesticular, median, triangular, 0.7 long by 0.8 wide. Ootype and Mehlis' gland to left of ovary. Oviduct joins ovary on the left, passes obliquely to posterior end of Mehlis' gland, then turns sharply forward to join ootype. Laurer's canal not observed. Right vitelline duct extends around anterior margin of ovary then passes between ovary and oviduct to vitelline reservoir; left vitelline duct passes obliquely forward to vitelline reservoir which joins oviduct before entering Mehlis' gland. Ootype lined Received for publication 9 May 1972. by flat epithelial cells which appear to be ciliated. Vitelline follicles small, abundant, distributed in U-shaped pattern along ceca dorsal to uterine folds and also filling a wide median area posterior to testes. Uterus composed of many transverse folds which fill space between gonads and ventral sucker; metraterm weakly developed, passes ventral to cirrus sac and ejaculatory duct and opens into genital atrium which is located anterior to genital cone. Genital pore ventral to posterior end of pharynx. Eggs oval, dark brown, operculated, thick-shelled, embryonated, 91 to 94 At long by 67 to 69 ,u wide; shell 7 ,u thick. Excretory vesicle Y-shaped, the stem 5 long, arms of vesicle long, sinuous, uneven in thickness, passing around anterior margin of oral sucker where they unite. Host: Ratfish, Hydrolagus colliei (Lay and Bennett, 1839). Habitat: Coelom. Type locality: Vicinity of San Juan Island, Washington. Type specimens: Holotype and serial frontal sections deposited in USNM Helm. Coll. Holotype No. 72266; paratype No. 72267.