A New Species of Proteocephalus Weinland, 1858, (Cestoda), with Notes on Its Life History

Abstract

From the spring of 1948 to the present time, the author has had the opportunity to examine for parasites more than 100 cut-throat trout, Salmo clarkii Richardson, taken from three small private lakes located near Stevenson, Washington. A total of five species of helminths have been collected from the trout thus far examined. Approximately 90 per cent of the fish were infected with Proteocephalus (P.) primaverus n.sp., and a parasitic copepod, probably of the genus Salmincola Wilson. Parasites encountered only rarely were the following: a trematode, Crepidostomum sp. (?), about twenty specimens from five fish; a cestode, Cyathocephalus sp. (?), one specimen; and an acanthocephalan, Neoechinorhynchus rutili (Mueller, 1780), eleven specimens from three fish. Since the proteocephalid is evidently an unreported species, its description is presented in the following section. The results of preliminary observations on the life history of this parasite are also included. All the helminths were fixed while still alive in either corrosive acetic or formalinalcohol-acetic solutions. If the worms were overly active, they were first allowed to relax in cold tap-water. The greater part of the anatomy of the new species was determined from studies of whole mounts stained in Kornhauser's hematin, while the arrangement of the interovarial organs was reconstructed from serial crosssections stained with Galigher's hematoxylin and eosin. All measurements are given in millimeters, unless otherwise stated, with average values included in parentheses. The drawings were prepared with the aid of a camera lucida. I take this opportunity to thank Dr. Ralph W. Macy for the many helpful suggestions he offered during the course of this study. I would also like to express my appreciation to Mr. Ernest Olson, for supplying the fish from which the parasites were collected, and to Mrs. Mildred S. Wilson, at the Arctic Health Research Center, Anchorage, Alaska, for identifying the copepod intermediate host of the new species. Proteocephalus (P.) primaverus n.sp. (Figs. 1-6) The strobila reaches a maximum length of about 93 and a breadth of 1.0. The scolex is unarmed and may or may not be expanded to form a definite head; it measures 0.68 long by 0.27 broad. The suckers are spherical and directed slightly forward; they measure 0.090-0.135 in diameter. A fifth sucker, apical organ, or rostellum are not present. The neck is not well differentiated from the rest of the strobila, except that it is not segmented; it is 0.15-0.23 broad by about 5 long. The surface of the strobila is non-spinous. There may be as many as 200 proglottids in a gravid specimen. The immature proglottids are approximately twice as broad as long and measure 0.080-0.28 long by 0.26-0.54 broad; the mature proglottids are quadrate and measure 0.43-0.84 long by 0.50-1.0 broad; the ripe proglottids may be square to twice as long as broad and are 0.70-1.75 long by 0.88-0.99 broad; the terminal segment is rounded posteriorly. The genital organs are similar to those of the other members of the genus and subgenus. The genital pores are marginal, from three-eights to five-elevenths of the segment's length from