The Egg, Miracidium, and Adult of Nematobothrium texomensis (Trematoda : Digenea)

Abstract

Nematobothrium texomensis occurs primarily in the gravid ovaries of three species of buffalo fishes. The adult is extremely filamentous, attaining a length of up to 2.5 m. It is almost devoid of muscle tissue, capable of little movement, and presumably absorbs nourishment through the cuticle. All sex organs are tubular. The ventral sucker is poorly developed and not recognizable in most specimens. There is evidence that when fish hosts spawn, pieces of worms containing eggs are discharged. Development outside the host is unknown except that miracidia force-hatched from the operculate eggs are of the didymozoid type. Development of N. texomensis is associated with the reproductive cycle of the host and the worm has never been found in a sexually immature fish. The worms die when the fish spawn or begin to resorb unspawned eggs. Eggs do not hatch in the juices of any snail species indigenous to Lake Texoma. Although some hatched in the gut of Succinea avara, no larvae developed. The first known collection of Nematobothrium texomensis consisted of two species from a buffalo fish Ictiobus bubalus taken from Lake Texoma by Dr. Virgil E. Dowell. The worms were profusely entwined through the lamellae of the ovaries, which were gravid, but considerable portions were free in the lumina of the ovaries and about 10 inches of one worm extended through the genital opening. They were filiform and so delicate that they were broken into many pieces during removal. The length of the combined pieces of the two specimens was approximately 5 m. McIntosh and Self (1955) reported this worm as the first known species of the Didymozoidae from a freshwater fish in the Western Hemisphere. McClelland (1955) reported Nematobothrium labeonis from the orbits of Labeo coubie, L. horie, and L. niloticus from the Nile River, and Yamaguti (1936) reported Philopenna higai from the dorsal fin and orbit of Sarcocheilichthys variegatus in Japan. These Received for publication 12 March 1963. * Present address: Department of Biology, Northern Michigan College, Marquette. t Present address: Department of Biology, Southern University, Baton Rouge, Louisiana. +t Work done at the University of Oklahoma Biological Station under support of Grant E 2849 (CL), National Institutes of Health. are the only species of the family now known to occur in freshwater fishes. Nematobothrium texomensis occurs in three species of buffalo fishes: Ictiobus bubalus, I. cyprinellus, and I. niger. While occasionally associated with mature testes, it is most commonly found in the lumina and lamellae of gravid ovaries. In a few cases, it has been found outside the ovary, between this organ and the peritoneum. Specimens frequently extend from one ovary to the other by way of the genital opening and may occur singly or as multiple infections. No living worms have been found outside the body cavity; the remains of dead specimens found immediately external to the peritoneum provide the only evidence that this parasite is a tissue migrant. DESCRIPTION OF THE ADULT Up to 2.5 m in length, 0.5 mm in diameter. Cuticle delicate and opaque to transparent. Socalled oral sucker nonmuscular and completely enclosed within the cuticle (Figs. 2, 12); pharynx present but nonmuscular (Figs. 2, 13); esophagus extends through approximately one-fourth the body length, surrounded by a single layer of epithelial cells (Figs. 2, 14) and divides into crura which extend to posterior end (Fig. 3). Intermittent clusters of glandular tissue surround esophagus (Fig. 15). Male and female genital pores located on a prominence lateral to oral sucker and closely adjacent to each other (Figs. 2, 12). Male duct nonmuscular (Fig. 14). Testes tubular, one con-