The Life History and Larval Development of Neoechinorhynchus saginatus Van Cleave and Bangham, 1949 (Acanthocephala: Neoechinorhynchidae)

Abstract

The life cycle of Neoechinorhynchus saginatus, an intestinal parasite of creek chubs, Semotilus atromaculatus, in eastern North Dakota is reported, with a description of development in the ostracod intermediate host. Eggs ingested by Cypridopsis vidua hatch, liberating the acanthors. These penetrate the intestinal wall and in 3 to 4 days begin metamorphosis in the hemocoel as immobile, unattached acanthellae. Juveniles appear to be fully developed by the 14th day, and feeding experiments indicate that such larvae are infective to chubs on the 16th day. The family Neoechinorhynchidae, order Eoacanthocephala, includes some two dozen species from North American fishes for which the life cycles of five are known. These include Neoechinorhynchus cylindratus, N. emydis, N. rutili, Octospinifer macilentis, and Paulisentis fractus. Only the last species fails to use ostracods as an intermediate host. Neoechinorhynchus saginatus, an intestinal parasite of the creek chub, Semotilus atromaculatus (Mitchill), was described from Wisconsin lakes and streams by Van Cleave and Bangham (1949). Fischthal (1950, 1952) also reported this species in Wisconsin chubs, and Meyer (1954) found it in fallfish, S. corporalis (Mitchill), in Maine. More recently, Voth and Larson (1968) reported N. saginatus from creek chubs of the Goose River, a tributary of the Red River in eastern North Dakota. Although creek chubs range from Montana to eastern Canada and south to the Gulf of Mexico, N. saginatus has been found in only three widely separated localities. Apparently, there have been no previous reports concerning the life cycle of this parasite. MATERIALS AND METHODS Creek chubs collected from the Goose River, near Portland, North Dakota, provided gravid females of N. saginatus. A second tributary (the Forest River) some 60 miles to the north possessed uninfected chubs used in feeding experiments. Received for publication 9 May 1969. * From a thesis submitted by Mr. Uglem to the University of North Dakota in partial fulfillment of the requirements for the degree of Master of Science, 1968. tPresent address: Department of Zoology, University of Idaho, Moscow, Idaho 83843. Ostracods were tested as potential intermediate hosts of N. saginatus since they serve in this capacity in four of the five known life cycles of neoechinorhynchids. Three species of ostracods identified as Cypridopsis vidua (O. F. Muller), Cypria maculata Hoff, and Potamocypris sp., collected from the Forest River, were successfully cultured for 2 years. They were exposed by allowing them to feed from 1 to 2 hr on aqueous suspensions of N. saginatus eggs in small finger bowls. The exposed hosts were then transferred for the duration of the experiment to large finger bowls of water held at 25 C under continuous illumination. These ostracods were examined periodically for developing parasites by making dissections using fine insect pins in a dilute solution of neutral red in 0.6% saline. One species of amphipod (Hyalella azteca), one species of copepod (Cyclops sp.), and four species of gastropods (Physa sp., Gyraulus sp., Lymnaea sp., and Ferrissia sp.) were also exposed to eggs and dissected periodically in an attempt to determine the specificity of the larval parasite. The chubs were inoculated by force-feeding infected ostracods with a polyethylene tube and syringe. Intermittent dissections were made to observe the growth and maturation of the parasites within the fish. Drawings were made from vital stained material with the aid of a camera lucida, by freehand, or from photomicrographs. All measurements are recorded in microns unless otherwise indicated. Permanent slide mounts of the ostracods, 16-day juveniles, and 46-day subadults have been deposited into the University of North Dakota Parasitology Collection with accession numbers 532535. Additional specimens are in the private collection of the senior author.