Comparative Morphology of the Genital Cones of Cooperia (Nematoda: Trichostrongylidae) from Cattle and Sheep in the United States with a Key to the Common Species

Abstract

Six Cooperia spp. had differences in the genital cones of their males sufficient to assign them to four basic groups: (1) C. punctata (previously determined-Stringfellow, 1969), C. spatulata, and C. curticei; (2) C. oncophora and C. bisonis; (3) C. surnabada; (4) C. pectinata. The genital cone of each has a small structure which is considered a reduced accessory bursal membrane. Differences in the genital cones are as follows: (1) The conformation of the sclerotized bars of the accessory bursal membrane distinguishes C. curticei from C. punctata and C. spatulata which are identical. (2) A sclerotized protuberance, absence of a basodorsal plate connection, a sclerotized sheet between the cloacal plate and dorsal plates, and a prominent ventrodorsal plate that fuses medially as a sheet over the dorsal part of the genital cone are diagnostic features of the genital cones of C. oncophora and C. bisonis which are identical. (3) C. surnabada has a basodorsal plate connection and a cuticular protuberance. (4) C. pectinata differs from all other groups in the conformation of the accessory bursal membrane, the sclerotized projections from the cloacal plate-dorsodorsal plate junction, the reduced ventral raylet, the cuticular protuberances from the basal apparatus, and the arched cloacal plate. A key to the six species of Cooperia common in cattle and sheep in the United States is included. Features of the genital cone have been used to a limited extent as generic and specific taxonomic characters for bursate nematodes (Shul'ts and Andreeva, 1953; Andreeva and Satubaldin, 1954). Their usual role is supplementary to other characters commonly used to identify these helminths. Most illustrations of the genital cone are incomplete (Baylis, 1929; Ransom, 1911), and where gross features are illustrated, the important details for separating the species are not included (Cram, 1925; Baylis, 1938). Andreeva (1958) illustrated morphologic differences encountered in the genital cones of species within certain genera and prepared an atlas in which genital cones are used as taxonomic characters. The value and extent, however, to which the genital cone can be used in taxonomic investigations is still uncertain because of the dearth of detailed knowledge available. Stringfellow (1969) selectively stained the genital cone of Cooperia punctata (von Linstow, 1907) Ransom, 1907, in section, enabling greater morphological detail to be seen than previously. He also showed that the structural components of the genital cone differ chemically. The present work compares the Received for publication 12 February 1970. genital cone and shows the value of the cone in separating those species of Cooperia that are common parasites of cattle and sheep in the United States. MATERIALS AND METHODS Males of Cooperia collected from cattle and sheep in the United States and deposited in the National Parasite Collection were studied with the aid of a compound microscope. The specimens were probably fixed in formalin and had been stored in a preservative consisting of 92 parts of 70% ethanol, 3 parts formalin, and 5 parts glycerin. Each specimen was compared with the descriptive literature and identified. Nine to 18 males each of C. curticei (Giles, 1892), C. bisonis Cram, 1925, C. oncophora (Railliet, 1898), C. surnabada Antipin, 1931, C. pectinata Ransom, 1907, and C. spatulata Baylis, 1938, were examined. Specimens were studied from the caudal, lateral, dorsal, and ventral aspects using glycerine, lactophenol, and rosaniline-HCl, respectively. Some of these were also embedded in paraffin, sectioned at 3 ,I, and stained with Mallory's aniline blue collagen stain (AFIP Manual, 1960). All measurements given herein are in microns and were determined from whole mounts and sectioned worms (Table I) with a calibrated ocular micrometer. All drawings were made with the aid of a camera lucida. Additional observations were also made on males of C. surnabada to confirm some of the unique structural details observed. These worms were collected from a steer and fixed in 10% formalin.