A New Species of Dipetalonema from the California Sea Lion and a Report of Microfilariae from a Steller Sea Lion (Nematoda: Filarioidea)

Abstract

Dipetalonema odendhali sp. n., Family Onchocercidae, is described from the California sea lion (Zalophus c. californianus). Adult worms were found in the intermuscular fascia of four hosts, and in additional sites-but not the heart-in one of them. Formalinized blood of one host contained microfilariae which are described. Conspecific filarioid parasitism among the California and Steller sea lions, northern fur seal (Callorhinus ursinus), harbor seal (Phoca vitulina), and northern elephant seal (Mirounga angustirostris) is considered. The demonstration of unidentified microfilariae in formalinized blood of a Steller sea lion (Eumetopias jubata) establishes a new host record for filarioid nematodes. A critical review of the literature indicates that there is a lack of documentary evidence of the existence of an enzootic infection with Dirofilaria immitis in the California sea lion, or, indeed, in native California domestic dogs. Microfilariae were examined in stained blood films of a captive California sea lion. The R-cell pattern was different from that of microfilariae of D. immitis. At the School of Veterinary Medicine on 13 September 1965, a necropsy was performed on a California sea lion, Zalophus c. californianus (Lesson, 1828). The animal was found to be heavily parasitized with nematodes in the intermuscular fascia, and in the thoracic and abdominal cavities. Enough specimens were collected to justify the description of a new species of filarioid nematode based on both males and females. The worms were fixed in hot, 70% alcohol to which 1% glacial acetic acid was added, and subsequently preserved in 70% ethyl alcohol with 5% glycerin. The species name is in honor of Stewart Odend'hal, a veterinary medical student, for his discovery of the nematodes, and for his contributions in anatomical research on sea lions. In the following description measurements are in microns unless otherwise indicated. Dipetalonema odendhali sp. n. (Figs. 1-1 1)